CHEMICAL EFFECTS ON WATER-USE EFFICIENCY OF ALFALFA … · 71T12,726 COLE, Darrell Franklin,...
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CHEMICAL EFFECTS ON WATER-USEEFFICIENCY OF ALFALFA (MEDICAGO SATIVA L.)
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Authors Cole, Darrell Franklin, 1941-
Publisher The University of Arizona.
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71T12,726
COLE, Darrell Franklin, 1941-CHEMICAL EFFECTS ON WATER-USE EFFICIENCY OF ALFALFA (MEDICAGO SATIVA L.).
University of Arizona, Ph.D., 1971 Agronomy
University Microfilms, A XEROX Company, Ann Arbor, Michigan
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED
CHEMICAL EFFECTS' ON WATER-USE EFFICIENCY OF
ALFALFA (MED.ICAGO SATIVA L. )
by
Darrell Franklin Cole
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF AGRONOMY
In Partial Fulfillment of the Requirements For the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 7 1
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
I hereby recommend that this dissertation prepared under my
direction by Parrel 1 Franklin Cole
entitled Chemical Effects on Water-use Efficiency of Alfalfa
(Medicaqo sat iva L.)•
be accepted as fulfilling the dissertation requirement of the
degree of Doctor of Philosophy
^ J < * / / £ / 7 # Dissertation Director £T~ Date '
After inspection of the final copy of the dissertation, the
following members of the Final Examination Committee concur in
its approval and recommend its acceptance:*
L. . A*' j'- u. i /•/• *w / / -A/" / ./ / l ,
''' S • <• v /a /n J~> o:
/a/z/r*
(Qikxt £. /0/7/pD 7 /
This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination.
STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED:
ACKNOWLEDGMENTS
The author is deeply indebted to Dr. Albert K.
Dobrenz for his constructive advice, suggestions, and his
untiring assistance throughout the course of graduate
study.
Acknowledgnient is given to the graduate committee,
Dr. Martin A. Massengale, Dr. L. Nea.1 Wright, Dir. Waltei"
S. Phillips, and Dr. Robert S. Mellor, for their guidance
and assistance in preparation of this dissertation.
The author also wants to thank Dr. L. Neal Wright
and Dr. Gerald 1-1. Luper for providing greenhouse and
growth chamber facilities.
Acknowledgment is given to the Department of
Agronomy for providing monetary funds to assist the author
in his graduate program.
The author expresses his gi-atitude to his wife and
children for their encouragement and patience during the
graduate program.
iii
TADLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS v
LIST OF TABLES viii
ABSTRACT xi
INTRODUCTION 1
REVIEW OF LITERATURE 3
Water Requirement of Alfalfa 3 Effect of Chemicals on Water-Use
Efficiency 4 Transpiration Rates of Alfalfa 5 Effect of Chemicals on Transpiration 6 Photosynthetic Rates of Alfalfa 8 Effect of Chemicals on Photosynthesis
and Respiration ........ 9 Effect of Chemicals on Alfalfa 11
MATERIALS AND METHODS 12
Lath and Greenhouse Experiments 13 Growth Chamber Experiments l6
Transpiration 17 Photosynthesis and Respiration 20
Field Experiment 20
RESULTS AND DISCUSSION . . . 25
Lathhouse and Greenhouse Experiments 25 Growth Chamber Experiments 34
Effect of GA on Transpii-ation 44 Effect of GA on Photosynthesis
and Respiration 49 Field Experiments 62
SUMMARY 83
REFERENCES 86
iv
LIST OF ILLUSTRATIONS
Figure Page
1. Plexiglass chamber used to measure the photosynthetic rates of entire alfalfa plants. Note the air intake near the base and exit near the top. The temperature probe is shown in the middle of the chamber 19
2. Plexiglass chamber used to measure photosynthetic and respiration rates of plants grown in the field 23
3> Effect of GA on length of individual internodes of alfa.l.fa grown in a controlled environment. Internodes arc numbered consecutively from cutoff level (one) to stem tip (ten) 40
4. Effect of GA 011 height of alfalfa stems grown in a controlled environment 4l
5- Effect of GA on the rate of stem elongation in alfalfa grown in a controlled environment 42
6. Transpiration rates for two clones of Mesa-Sirsa alfalfa grown .in a controlled environment 45
7. Effect of GA on the transpiration rates of Mesa-Sirsa alfalfa grown in a contro1Ied environment 47
8. Effect of GA on the transpiration rates o f t wo c. lone s o f M e s a - S i r s a a I f < 1 1. f a grown in a controlled environment 48
9. Effect of GA 011 the percentage moisture and total forage of Mesa-Sirsa alfalfa grown in a cont rolled environment 52
10. Effect of GA 011 the stem-petiole and leaflet, weights of Mesa-Sirsa alfalfa grown in a controlled environment 53
v
vi
LIST OF ILLUSTRATIONS--Continued
Figure Page
11. Effect of GA on transpired water and water requirement of Mesa-Sirsa alfalfa grown in a controlled environment 5 4
12. Effect of GA on leaflet to stem-petiole ratio and specific leaf weight of Mesa-Sirsa alfalfa grown in a controlled environment 55
13• Effect of GA on respiration rates of Mesa-Sirsa alfalfa grown in a controlled environment. Left) ing CO^ dm~2 hr-1. Right) nig ^2 ®
l4. Effect of GA on pliotosyntlietic rates of Mesa-Sirsa alfalfa grown in a controlled environment. Left) mg CO2 dm~2 hr-1. Right) mg COg g--*- hr-1 57
15* Effect of GA on the yield of Mesa-Sirsa alfalfa grown under field conditions. Data taken from an area of .19 rn^ 63
l6. Effect of GA on stem length and secondary branching. l) Control. 2) Treated .... 66
17* Effect of GA on alfalfa leaf anatomy. Note the increased width find the arrangement of palisade and spongy mesophyll cells (1250 X). Upper) Treated. Lower) Control- 69
18. Effect of GA on raceme and sepal elongation. l) Control. 2) Treated 71
19. Effect of GA on photosynthesis (mg CO2 dm~2 hr-1) of alfalfa grown under field conditions 72
20. Effect of GA on respiration (mg CO2 dm_2 hr-1) of alfalfa grown under field conditions 73
21. Effect of GA on specific leaf weight (SLW) of alfalfa grown under field conditions 7'j
vii
LIST OF ILLUSTRATIONS--Continued
Figure Page
22. Chlorosis and increased height of Mesa-Sirsa alfalfa following GA application under field conditions 76
23. Effect of GA on per cent trarismittance of a chlorophyll extract of Mesa-Sirsa alfalfa 79
2'i. Photograph showing the separation of free sugars by thin layer chroiiuitography. Standards were prepared at a concentration of 2 nig/ml . Maltose was spotted with 10 and 25 |i.l , Mj_ and M2, respectively. Sucrose (S) and fructose (F) were spotted with 25 jJ,l and the unknown was spotted with 5, 10, 25, and 50 jxl , la, lb, 1c , and Id, respectively 8l
LIST OF TABLES
Table Page
1. Chemicals, rates, and methods of application used on seeded plants of Mesa-Sirs a alfalfa in a controlled greenhouse environment l'l
2. Chemicals and rates used on seeded plants of Mesa-Sirsa alfalfa in a lathhouse environment 15
3- Effect of various chemicals on water-use efficiency of Mesa-Sirsa alfalfa grown in a greenhouse environment 26
k. Effect of various chemicals on stem-petiole and leaflet weight of Mesa-Sirsa alfalfa grown in a greenhouse environment 27
5. Effect of various chemicals on total forage per plant and leaflet to steni-petiole ratio of Mesa-Sirsa alfalfa grown in a greenhouse environment 29
6. Means of water-use efficiency, total forage, and stem-petiole tissue as affected by various chemicals applied to Mesa-Sirsa alfalfa grown in a lathhouse environment at the Tucson Plant Materials Center 31
7. Means of leaflet to stem-petiole ratios, height, and transpired wat er as affected by various chemicals applied to Mesa-Sir Set a I l'al Ca grown in a lathhouse environment at the Tucson Plant Materials Center 32
8. Effect of GA on water requirement values of alfalfa based on yield components and total forage for five harvests in a controlled environment 35
viii
ix
LIST OF TABLES - -C 0111 inu ed
Table Page
9. Effect of GA on dry weight of stein-petiole, leaflet, and total forcige production of alfalfa for five harvests in a controlled environment .... 36
10. Effect of GA on transpired water, 1 eaf].et to stem-petio 1 e .1"atios , and height of alfalfa for five harvests in a controlled environment 37
11. Effect of GA on the anatomy of alfalfa stems 4-3
12. Analyses of variance for the transpiration data, water per cm^ per hr, measured on Mesa-Sirsa alfalfa in a program controlled environment 50
13 • Effect of GA on several, characteristics measured on two clones of Mesa-Sirsa alfalfa grown in a program controlled environment 51
1'i. Summary of the analyses of variance for testing the effect of GA on various characteristics measured on Clone 2 of Mesa-Sirsa alfalfa in a controlled environment 58
15. Effect of GA on carbohydrate fractions and protein content of roots from Clone 2 of Mesa-Sirsa alfalfa grown in a controlled environment 6l
16. Effect of GA on yield of Mesa-Sirsa alfalfa grown under field conditions at Tucson, Arizona for two harvcst periods in .1970 6'±
17* Effect of GA on yield components and leaflet to s t em-pe t.io.l e ratios of Mesa-Sirsa a.l fal. fa grown under field conditions 65
l8. Effect o C GA on the anatomy of Mesa-Sirsa alfalfa leaves and stems 68
X
LIST OF TABLES--Continued
Table Page
19* Effect of GA on chlorophyll content of primary and secondary leaves of Mesa-Sirsa alfalfa 77
20. Effect of GA on carbohydrate fractions and protein content of roots of field grown Mesa-Sirsa alfalfa 80
ABSTRACT
Plants of Medic.ago sativa L. cultivar 'Mesa-Sirsa'
were grown in lathhouse, greenhouse, growth chamber, and
field environments and were used to evaluate the effect of
various antitranspirant and growth regulator chemicals on
water-use efficiency and on physiological, morphological,
and anatomical characteristics. Growth regulators used
were gibberellic acid (GA), indoleacetic acid (IAA) , and
( 2-chloroethyl) trime thy .1. ammonium chloride (CCC). Anti
transpirant chemicals were phenylinercuric acetate (PMA)
and dodecenylsuccinic acid (DSA). Gibberellic. acid
significantly lowered the water-use efficiency of alfalfa
in all environments. Indoleacetic acid, CCC, PMA, and DSA
did not reduce the amount of water required to produce a
unit of dry forage. The antitranspirant chemicals did not
reduce the amount of water transpired, and further, DSA
caused plant damage when used as a foliar spray.
Gibberellic acid significantly increased the amount
of stem tissue produced in all environments which resulted
in more total dry-forage production. No effect weis found
on the amount of leaflet tissue produced except in experi
ments where GA stimulated secondary branching.
Flowering was promoted by GA apjilication and
morphological changes were evident in the flowering raceme.
x.i
Pith cell length, leaf thickncss, internode length, stem
length, and rate of stem elongation were increased by GA.
The effect of GA on transpiration was influenced
by soil moisture level. Transpiration rates were higher
on plants treated with GA when 30 to 55% of the available
soil moisture was depleted.
Photosynthesis, respiration, and specific leaf
weight (SLW) were significantly decreased by GA treatment.
— 2 —1 Photosynthetic rates (mg CO^ dm " hr ) were always less
on plants treated with GA. However, when the data were
expressed on a unit of dry leaflet tissue, GA did not
consistently reduce photosynthesis. The time of measure
ment after treatment and the ago of the plants influenced
photosynthesis aiad respiration rates. The SLW was lower
on plants treated with GA.
Gibbcrellic acid caused a reduction in the chloro
phyll 13 content of alfalfa leaves. Extreme chlorosis was
noted under field conditions.
Roots from alfalfa plants sprayed with GA had lower
percentages of free and acid-hydrolyzable ca.rbohydratcs
when grown under growth chamber and field conditions.
Sucrose was the only sugar found in the 00% ethanol
extract. Percentage of crude protein was higher in the
roots of plants treated with GA.
INTRODUCTION
Alfalfa (Medicuft'o satri.va L.) .is the most .important
irrigated foi~age crop grown in Arizona. Alfalfa has the
highest consumptive use of water of all the major crops
grown in Arizona (19). Consumptive use of water by
alfalfa is high because of a long growing season and high
yields. Also, in the semiarid climate evaporation is high.
Alfalfa is a high quality feed for livestock con
sumption. However, if water becomes limited alfalfa
production may be shifted to an alternative forage which
has a lower water consumption. Therefore, it would be
highly desirable to find an alfaIf a cultivar that was more
efficient in water utilization. If water consumption by
present high yielding cu.ltivars could be reduced without
reducing yields, or yields could be increased without in
creasing water consumption, then the production of alfalfa
in areas with limited water would bo greatly enhanced. The
above factors would also apply to other crops in either
natural rainfall or irrigated areas. The terms water
requirement and water-use efficiency are used inter
changeably .
This study was initiated with the following
ob j oct .i.vcs :
1
To determine the effect of antitranspirant and..
growth regulator chemicals on water-use efficienc
of alfalfa.
To determine the effect of antitranspirant and
growth regulator chemicals on morphological,
physiological., and anatomical characteristics of
alfalfa.
REVIEW OF LITERATURE
Water Requirement of Alfalfa
There are approximately 80,000 hectares of alfalfa
in Arizona. Alfalfa in the Salt River Project utilizes
188.7 cin ( 7 'i. 3 inches) of water per year (19) - Alfalfa
production creates a large demand for water in an area
where water is becoming limited for agricultural purposes.
The water requirement of alfalfa varies with
different environmental conditions (9)* The literature on
water requirement in both greenhouse and field conditions
has been reviewed extensively (l, 11, 32). The water re
quirement for alfalfa varied from 657 to l,068over a 7-year
period ('±1) . Al-ICawaz (l) reported significant differences
in the water-use efficiency of alfalfa grown with varying
moisture regimes. Genotypes within a cultivar exhibited
as much variation as differences among cultivars (ll).
Minimum water-use efficiency values were associated with
maximum production of dry forage in most species.
Kelley (33) listed several factors which .influence
the water requirement of plants such as soil moisture,
soil type, fertility, and various climatic conditions.
Other factors such as disease, salinity, chemical agents,
and stage of growth also influence water utilization. Thorn
3
cuid Iloltz (6:i.) concluded that any condition which disturbed
the normal processes of the plant affected the water
requirement.
Effect o f Cheriiic- a Is on Water-Use Efficiency
Several chemicals applied to various species have
affected water utilization (59)• Plants of sorghum
(Sorghum vulgare Pers . ) treated with dalapon (2,2-dich.loro-
propionic acid) had a higlier water requirement in l6 days
(3376) compared to the nontreated (65^) plants (68). Coiner
(.12) found no effect of pyrazon (5-ami]io-'l-chloro-2-phenyl-
3(2H)-pyridazinone) on the water-use efficiency of sugar-
beet (Bet a vulgaris L.) when grown in a greenhouse environ
ment. Olsen et al. (48) used hexodecanol and octodecanol
on corn (Zea mays L.) and found no reduction in water
utilization; however, production was lower at high rates
of application.
Brcngle (8) found no effect of phenylmercuric
acetate (PMA) on water use by wheat (Tr.itic.u111 nestivum L. ) ,
but damage to the ears and a slightly lower yield were
observed. Swoet orange (Citrus sinensIs Blanco) treated
with latex or silicone coatings exhibited a lower water
requirement (39)* These investigators reported leaf burn
and morplio.log.ical changes in the treated plants.
Plant and llalevy (53) used two growth retarding
chemicals on wheat and found no effect 011 the water-use
efficicncy. Other experiments with o. growth retardant have
shown an interaction between chemical treatment and
moisture regime of the soil (^k).
Ti'ansplratlori Rates of Alfalfa
Very little information is available in the
literature on the transpiration rates of alfalfa expressed
on a leaf area basis. Most of the literature on water use
by alfalfa deals primarily with total consumptive use or
the evapotrans pir at ion rates per day.
Ehrler (.17) reported differences in the amount of
water absorbed by cultivars . 'Lahontan 1 utilized less
water than 'Moapa' in two experiments; however, no values
were reported for either cultivar. lie further reported as
the saturation deficit varied from 0 to 50 nib, transpiration
_ 2 -1 increased from 0 to 300 g m hr . He reported a decrease
in transpiration rates as root temperatures were lowered.
Al-Kawaz (.1) found rates among genotypes of 'Mesa-
— 2 —1 Sirsa 1 to vary from 1.00 to 'l.l4 g H^O dm hr However,
these results should be viewed with caution as they are
single plant observations in an unreplicated experiment.
Al-Kawaz showed a decrease in transpiration rates as the
plants .reached maturity when averaged over all genotypes
within a growth stage.
6
Effect of Chemicals on Transpiration
No data are available on the transpiration rates of
alfalfa per unit of leaf tissue as affected by chemical
treatment. Hales (26) showed a significant reduction .in
the total amount of water used by alfalfa when treated with
various antitranspirants; however, these data gave no
indication of the amount transpired per unit area of leaf.
Some chemical treatments caused foliar damage and reduced
growth which may have reduced the total amount of water
utilized.
Zelitch and Waggoner (7'0 studied the effect of
various chemicals on the transpiration rate of various
species. They found PMA and other compounds reduced
transpiration in some species. For example, PMA reduced
transpiration of tobacco (N i c o (. :i. an a t abacuin L.) in both
leaf disks and intact leaves (73, 7^). Photosynthetic and
the relative growth rates varied with different environ
ments. Shimshi (5$) confirmed the data of Zelitch and
Waggoner where he noted a reduction in transpiration of
tobacco and Helianthus animus L. when grown in an open
environment. Turner and Waggoner (Gh) reported a 10%
reduction in water use by Plnns resinosa Ait. when sprayed
with PMA under field conditions.
Friesen and Dew (ii2) observed a reduction in
transpiration of a weed species when treated with two
herbicides . The slower ,acting herbicide did not reduce
transpiration as rapidly as the other herbicide. Todd and
Propst (62) noted a reduction in transpiration of leaves
Asrhich were subjected to treatment with o'/->one and ozonated
hexene . Atrazine [ 2-ch.lor o-4- ( ethyl amino ) -6 - ( is opropyl -
amino)-S-trianine] caused a reduction in transpiration of
corn and soybeans (Glyc ine max Morrill) by h-h and 67%,
respectively (59)-
Livne and Vaadia (35) found a differential response
in barley (Hordeum vulgare L.) depending upon the type of
chemical used. An increase in transpiration occurred with
kinetin and gibberellic acid (GA), no response was noted
when adenine and indoleacetic acid (1AA) were used, and a
reduction in the rate occurred when actinomyc.in D and
puromycin were applied to the .leaves. Luke and Freeman
(37) observed no effect on transpiration of excised oat
(Avena satlva L.) leaves when treated with GA; however, a
stimulation was noted when cytokinins were applied. Later,
these researchers were unable to show an effect of
cytokinin on dicotyledonous species (38). Nieinan and
Bernstein (46) reported tin increase in transpiration of
bean leaves treated with GA.
The use of long ch;iin alcohols 011 corn and barley
reduced yield more than transpiration ('l7, 48). Gale,
Roberts, and llagctn (24) reviewed the literature on the use
of alcohols as ;intitraiispirajits and concluded, on the basis
of 17 repoi'ts in which all but one found a reduction in
8
growth, that these materials were unsuitable as effective
antitranspirants. These alcohols offer more resistance to
CO^ exchange than to water movement.
Photosynthetic Rates of Alfalfa
The photosynthetic rate of alfalfa varies with the
age of leaves, environment, and the leaf area index (LAI)
(23, 69)• El-Tabbakh (l8) reported no differences between
field and greenhouse plants in rate of assimilation.
He reported a wide range in rates among cultivars , 23 to 5^
— 2 —1 mg COr> dm hr ' , and Mesa-Sirsa had an average of 43 mg
— 2 -1 COg dm hr when measured at 32 C.
Potassium nutrition has been shown to be important
in the photosynthetic process (13)• As potassium increased
from 0 to 5%, an increase in photosynthetic rate was found
— 2 — 1 (8 to 20 mg dm hr "). Stomatal closure may have been
responsible for the low rates at low potassium levels.
Fuess and Tesar (23) found 3-week-old leaves were
less than one-seventh as active as 5-day-old leaves in
oxygen evolution. These investigators also found an
increase in LAI as the plant reached the bud stage of
development. Wilfong, Disown, and Blaser (69) reported
that photosynthesis .increased as the LAI increased to about
4 and then the rates leveled off. Maximum rates occurred
when 915% of the incident light was intercepted.
9
Pearce, Brown, and Blaser (5l) found a difference
in pliotosyntlietic rates between plants grown in the field
and in growth chambers. Young leaves in the field had a
- 2 - 1 rate of 52 compared to 35 mg C0^ dm hr for the same
age leaves in growth chamber environments. However, when
the rates were expressed on a dry weight basis no difference
existed. This difference in results can be accounted for
2 by the specific leaf weight (SLW, mg/cm ). The SLW was
larger in the field than in the growth chamber. Specific
leaf weight increased as the leaves matured (5l)« Pearce
et al. (52) showed a positive correlation between SLW and
pliotosyntlietic rates. Their data showed that the photo-
-2 -1 synthetic .rate varied from 20 to 50 mg CO dm hr ' as the dt
SLW changed from 1.9 to 5»3*
Al-Kawaz (l) reported differences among genotypes
of Mesa-Sirsa in both photosynthesis and respiration. The
rates of both physiological processes decreased with
maturity.
Effect of Chemicals on Photosyivthes:i.s and Res p i rat1on
G.ibberel lie acid has increased the respiration of
hypocotyls and cotyledons in Cucunils sat.i.vus L. and
decreased the rate in the radicle. Also, an increase in
catalase activity was fouvicl (27). Troltarne and Stoddart
(63) found an inci-oa.se in the activity of ribulose-1 ,5-
diphospliate carboxylase i.11 Trifol.j um pr a tense L. They
10
contributed the increase to an overall effect in promoting
protein synthesis rather than a specific action on the
enzyme. These researchers suggested GA may be part of a
system mediating the pbytocliromc system.
Other investigators (25, 'l-2) found no effect on
1 'i manometric measurements of leaf disk and ' CO^ uptake on
leaves treated with GA. However, Coulombe and Paquin (15)
noted an .increase in respiration and photosynthesis 1 to 2
hours after GA application and maximum effect was noted
5 to 6 hr after treatment. Alvim (2) reported an increase
in net assimilation rates (NAR) of beans (Phas eolus vulgaris
L.) when treated with GA. Ousheva, Popov, and Manolova
((l9) found an increased accumulation of biomass of Ch lor el let
when GA was applied to the media.
Photosynthesis was inhibited when two herbicides
were applied to Scenedesnns sp. The rates were mediated
by light intensity (65) • Todd and Pr*opst (62) found a
reduction in photosynthesis when ozone was applied to leaf
tissues.
Humphries, Weibank, and Witts (29) found a reduc
tion in NAR of wheat when treated with CCC [(2-chloroethyl)
t r i m e t li y 1 a mm o n i u 111 chloride.]. Plienylmercuric acetate has
been shown to cause ci reduction in photosynthetic rates of
different plant species (57, 59)•
Effect of Chemicals on Alfalfa
Massengale and Medlar (4o) found that TIBA (2,3,5-
triiodobenzoic acid) and 2,4-,5-T ( 2 , k , 5-triclilorophenoxy-
acetic acid) increased stem elongation and IAA caused a
reduction in stem length. No effect on the number of nodes
per stem was found; however, leaf morphology showed some
variation from the nontreated plants. Yeh and Bingham (70)
showed that IAA reduced stem elongation of two genotypes.
These researchers found a clonal interaction in the number
of racemes and florets , and stein height when treated with
GA and TIBA. Other investigators (.10, 21, 71) showed an
increase in stem height in response to GA application.
Corns (I'l) found no response of 'Gi-'imni1 alfalfa to
GA treatment. However, Finn and Nielsen (2l) reported a
.reduction in root growth and an increase in total protein
even though a decrease in percentage protein on a dry
weight basis was found. Carlson, Sprague, and Washko (10)
found a reduction in total carbohydrates when alfalfa was
treated with GA. Yeh (7-1) reported that carbohydrate
levels varied in response to GA application. lie found an
increase in plants grown in the field and a decrease in
greenhouse grown plants.
MATERIALS AND METHODS
Plants of Mesa-Sirsa were used to investigate the
effects of growth regulator and antitranspirant chemicals
on water-use efficiency, transpiration rates, photo
synthesis, and anatomical features of alfalfa. Studies
were conducted in greenhouse, latlihouse, and gi-owth chamber
environments.
The method of plant cvi.lture was basically the same
in all experiments. Plants were grown in plastic pots with
a hole 1.2 cm in diameter at the base of each pot to alloAf
for drainage during plant establishment. Pea gravel was
added to cover the bottom and a known weight of a mixture
of desert Mohave clay loam soil (Typic Ilap.l argid) , peatmoss,
and organic fertilizer was added to each pot. The ratio of
constituents in the soil mixture was 3 parts soil , 1 part
peatmoss, with .100 g of organic fertilizer (milorganite)
and 3 g of sulfur per 20 kg.
In all experiments there was one plant per pot
which was cut 7 cm above the soil surface at the beginning
of each trial. During plant establishment forage above
the 7 cm level was removed at the 1/10 bloom stage.
Styrofoam was added to the surPace of each pot to reduce
evaporation (.13.) and the pots were watered to bring the
soil to field capacity (27%) at the start of each trial.
13
The experimental design wcis a randomized complete block in
all experiments. Each pot was weighed daily and re-
watered when 55/° of the available: soil moisture had been
utilized. The plants wore harvested at 1/10 bloom and in
each experiment the amoimt of dry forage (80 C for 2k hr)
was divided by the amount of water utilized to detex-mine
the water requirement. Leaflet to stem-petiole ratios were
calculated in all experiments. Height of steins and number
of nodes per stem were determined prior to harvest. Per
centage N was measured by the micro-lcjeldahl method (3) and
multiplied by 6.25 to estimate crude protein percentage.
Lath and Greenhouse Experiments
Rates and methods of application of chemicals used
in a greenhouse environment are shown in Table 1. The
abbreviation following cach chemical name will be used in
future discussion. All plants received the first chemical
application when regrowth Wcis k cm tall. The second
application was applied k days later. Plants used in this
study were 6 months old and the experiment was conducted in
January, 1969- Average maximum and minimum temperatures
were 3-1 and .1.8 C, respectively. Average relative humidity
was 50/n. Six treatments represented once in each of eight
blocks were us o< 1.
Inform .it ion presented in Table 2 gives the rates
and chemicals used in a lathhouse environment at the Tucson
Table 1. Chemicals, rates, and methods of application used on seeded plants of Mesa-Sirsa alfalfa in a controlled greenhouse environment.
Application rates per plant
Methods of Chemical* application Concentration Low High
Gibberellic acid (GA) f o 1 i ar spray 100 mg/lit er 1 ml 2 ml
Indoleacetic acid (IAA) foliar spray 100 mg/liter 1 ml 2 ml
Phenylmercuric acetate (PMA) foliar spray 1 X H
O 1
1 ml 2 ml
Dodecenylsuccinic acid (DSA) foliar spray 5 X 10 5 M 1 ml 2 ml
(2-chloro ethyl) trimetliylammonium chloride (CCC) soil drench 223 mg/100 ml 100 ml 200 ml
Water foliar spray 0 1 ml 2 ml
*A11 chemicals were used in an aqueous solution.
Table 2. Chemicals and rates used on seeded plants of Mesa-Sirsa alfalfa in a lathhouse environment.
Rates+
Chemical 1 2 3 k
GA* 100 mg/liter 200 mg/liter 300 mg/liter zi00 mg/liter
P>1A* 1 x 10~3 M -4
1 x 3.0 M 1 x 10"5 M 1 X 10~6 M
ccc* 2 M 1 M 1 x i
10~2 M 1 X H
O 1 I-F
-
2
Water plus Tween 20 0 . 2%
W at er 0
*0.2% Tween 20 added to each aqueous solution of chemicals.
+1 ml of each solution was applied as a foliar spray.
H
16
PJ. ant Materials Center in June, 19 6 9 • The numb er of
chemicals was reduced since there was either no effect or
plant damage noted from the chemicals described in Table 1.
The GA, CCC , and control treatments were applied on June
23, 19^9 and the PiMA was applied on June 30, 19^9 • The
plants in this study were 3 months old. Average maximum
and minimum temperatures were 'll and 19 C, respectively.
Average relative humidity was 52%. Fourteen treatments
represented once in each of I'l blocks were used.
Growth Chamber Experiments
Several growth chamber experiments were conducted
to elucidate the significant effect of GA on water utiliza
tion of alfalfa. One of the first objectives was to
determine if a carryover .response could be measured on
subsequent regrowth. Seeded plants of Mesa-Sirs a were
grown for five consecutive harvests. Two groups, each with
12 plants, were grown in a controlled environmental chamber.
The day and night temperatures were 26 + 1 and l6 +_ 1 C,
respectively, during the 16 hr photoperiod. Light
intensity was 185•8 lux at plant height. The first growth
period was to adjust the piants to the different conditions
of the growth chamber-. During the second growth period,
Group 1 was sprayed with L ml of GA (150 nig/liter) when
regrowth was approximately 3 cm in height. A second
application was applied 'i days later. Group 2 was treated
in the same manner during the fourth growth period. Mar-
vests 3 and 5 were used to evaluate carryover effects.
Height measurements were made at 2-day intervals during
each treated harvest. Stem tissue was collected from the
second harvest to measure the effect of CIA on the anatomy
of alfalfa stems. The samples (0.5 cm) were collected from
an area 1 cm above four consecutive nodes located on the
basal portion of the tallest stem of each plant. Cross
sectional and longitudinal sections were stained with
safranine and fast green according to techniques described
by Johansen (31)* Cells were measured using a calibrated
ocular micrometer.
Transpiration
To measure the effect of GA on transpiration,
propagules of two Mesa-Sirsa clones were established.
These clones were selected for vigorous growth when
spaced planted in the field. Ten propagules of each clone
were grown in the same environmental conditions previously
described. Three con.secut.ive harvests were taken.
The first harvest was used for plant adjustment to
the environment and help in establishing uniformity among
propagules. Two days prior to the second harvest, half of
the propagules of each clone were sprayed with 3 nil of GA
(.150 mg/liter) to wet all leaC foliage. The light period
was from 0700 to 2300 hr . The spraying was in a d e at 2300
18
hr and a3.1 plants were watered to field capacity. The
plants were weighed at periodic intervals to determine the
amount of water loss during the next light period and
rewatered when 55% of the available moisture had been
utilized. Rewatering was at 1700 hr. This procedure was
repeated for 2 consecutive days.
On the third day after the initial spraying, photo-
synthetic measurements were made in an open system using a
Beckman 215 Infrared Gas Analyzer. Measurement of the
entire plant was accomplished by using the plexiglass
chamber shown in Fig. 1. Two air intake-holes were located
near the base and the air was drawn out through a hole near
the center-. Leaf eirea and specific leaf weight (SLW) were
measured by Xeroxing all the leaves on two randomly
selected steins from each plant and determining cm area to
weight ratio. Photosynthesis was expressed as the mg of
2 C0o per dm per hr and also on a dry leaf weight basis C*t
(80 C for 24 hr). Transpiration rates were expressed as
the mg of wat er loss per unit of leaf area per hour.
Photosynthesis and transpiration of the I.eaves below the
7 cm cutoff level were accounted for in the data.
Treatment of the propagules during the third
reg.rowth period was the same .as in the second period.
Propagules wore 5 months old at the beginning of this
experiment.
Fig. 1. Plexiglass chcimber used to measure the photo-synthetic rates of entire alfalfa plants. Note the air intake near the base and exit near the top. The temperature probe is shown in the middle of the chamber.
20
Photosynthesis and Respiration
In the previous experiments, clones reacted differ
ently to GA treatment. To obtain additional information on
photosynthesis and respiration of GA treated plants, a
study was conducted in Avhich 2h propagules of Clone 2 were
used. The environmental conditions of tb" growth chamber
were the same as those described. The plants were grown
for two consecutive harvests.
The first harvest was used for the plants to adjust
to the environment. During the second growth period half
the plants were sprayed with 1 ml of GA (150 mg/liter) five
days after cutoff when regrowth had begun. The plants were
sprayed at 2300 lir. The treated plants were sprayed again
h. and 8 days later with the same concentration but with a
volume of 1 and 3 nil, respectively, to wet the leaves.
Photosynthesis and respiration data were collected
on four plants of the sprayed and control plants three
times at 4-day intervals beginning the day following the
.initial spray treatment .
All plants were watered to field capacity at 2300
hr of the day preceding measurement.
F i e 1 d E.vp o r ini ent
The field research for this study was conducted at
the University of Arizona Campbell Avenue Farm, Tucson,
Arizona. In October of .1 969 , one border was seeded Av.ith
21
certified Mesa-Sir,Sci alfalfa at 22. k kg/ha. The border was
irrigated to insure sufficient moisture for germination and
einer gene e .
The border was 7-92 x 30 . ;l8 m and it was divided
into six plots (3.66 x 8.53 m)• The plants were allowed to
establish during the winter and the first forage was
removed on April 10, 1970. During the establishment
period, irrigation was managed to prevent water stress.
The border was irrigated during the period of study at the
beginning of each regrowth period . Sufficient water was
applied to fill the entire root zone to field capacity.
No treatments were applied to the regrowth which
developed during the period between April 10 and 25 when
the forage was again removed.
The treatments on the first harvest for data
collection were made on May 15, l6, and 23• Gibberellic
acid was applied with a pressure sprayer at the rate of
2 liters (150 mg/liter) per plot. Three plots wer e sprayed
and three served as the control plots. Forage from a
2 .19 '» and soil moisture samples to a depth of 1.22 m were
taken at 'i-day intervals beginning on May .1.6 and lasting
through May 28.
Ten stems were selected at random from each plot
on May 28 and were used to determine height and internode
length. Stem and Jeaf samples were collected from the
fourth and seventh node and internode from the base to
22
measure the effect of GA on anatomical characteristics.
Also, a leaf was collected fi'om the stem apex. The center
leaflet of each leaf was used in all measurements.
During the second harvest the control plots were
divided in half in order to evaluate the regrowth on the
treated plots of the first harvest. Gibberellic acid
application was the same as that previously described
except the volume was reduced to 1 liter per plot.
Gibberellic acid was applied at k-day intervals beginning
on June 8 and lasting until June l6.
Forage and moisture samples were taken only on
June 21. Beginning on June 9, and at two intervals there
after until June 21, one stem was selected at random from
each plot, placed in a 125 ml polyethylene bottle filled
with water, and used to determine photosynthetic and
respiration rates. The stems were cut .in the field at 2000,
held in a dark room at 25 C, and measurements were made the
following day between 0800 and 1000 hi'. A plexiglass
chamber shown in fig- 2 was used in the system previously
described for the growth chamber studies.
On June 21, ten stems were selected at random from
each plot for height and internode length measurements.
Additional forage was collected for chlorophyll determina
tions as described by Seitz (5^0 • Chlorophyll determina
tions were made on main and secondary leaves separately.
23
Fig. 2. Plexiglass chamber used to measure photosynthetic and respiration rates of plants grown in the field.
2'l
2 Roots from a .19 in ai~ea in all plots were dug at
the end of each regrowth period. The roots were immedi
ately washed, placed on dry ice, and stored at 0 C until
they were dried in a freeze-dryer. The samples were ground
to pass through a ll0 mesh screen and carbohydrate determina
tions were made using extraction techniques described by
Dobrenz (l6) and color.imetric determinations described by
Yemon and Willis (72). Qualitative determinations on the
free sugar extract were made by thin layer chromotography
methods described by Stahl (6o). The samples were spotted
on plates coated with silica gel G and impregnated with
0.02 M sodium acetate. The plates were developed with
solvent No. 6 described by Stahl (60). The sugars were
detected with aniline-diphenylamine spray reagent (60).
RESULTS AND DISCUSSION
IJathhouse and Grcnnliouse Experiments
Gibbe.roI.lic acid significantly affected the wate.r-
us e efficiency of alfalfa (Table 3) • Tlie lowest water
requireinent va.Iue was found with the high rate of CIA
application. Plants treated with GA were lower (P - .05)
in water requirement than all other plants treated with
antitranspirnnt and growth regulator chemicals when
averaged over both rates. No effect on water requirement
was found when the plants treated with PMA, IAA, CCC, and
DSA were compared to the control plants,
Plants treated with GA produced the most stein-
petiole tissue (Table k) . A reduction .in stem-petiole
weights were found with the high rate of chemical, applica
tion. A significant chemical by rate interaction showed
that GA treated plants produced more stem-petiole tissue
at the high rate of application.
None of the chemicals influenced the amount of
leaflet tissue produced when averaged over both rates
(Table h) . However, a chemica l, by rate interaction, was
evident. Maximum and minimum leaflet production was noted
OJI plants treated with CCC at the low and high .rates,
respectiv e1y.
26
Table 3* Effect of various chemicals on water-use efficiency of Mesa-Sirsa alfalfa grown in a greenhouse environment.
Water-use efficiency
Chemic al
Rate CCC GA IAA DSA PMA Control Mean
Low 912* 893 939 ab ab a
High 1072 764 1071 a b • a
992 a 829 b 1005 a
915 9'I8 104-5 9Z12 ab a a
1043 986 1010 991 a a a
979 a 967 a 1027 a
*Values within rates and means followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
27
Tabic k. Effect of various chemicals on. stoni-petio.le and leaflet weight of Mesa-Sirsa alfalfa grown in a greenhouse environment.
Chemical
Rat e CCC GA IAA DS A PMA Control Mean
Stem-petiole weight , ,c r
Low .81 * ab
.75 .80 ab ab
• 70 b
• 72 b
.62 b
• 73 a
High • 51 b
1.00 .52 a b
•51 b
.60 b
.60 b
.62 b
M e an .66 b
.87 .66 a b
. 6l b
. 66 b
• 6l b
Leaflet weight, g
Low • 7'i a
•52 .73 ab a
. 6 6 ab
• 57 ab
.60 ab
.64 a
Hi gh .'19 b
•71 .51 a ab
• 51 ab
• 56 ab
.56 ab
.56 a
.62 a .62 a .62 a .58 a .56 a .58 a
^Values within rates and means followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
28
Total forage production was lower (P = .05) when
high rates of these chemicals were applied (Table 5)•
Maximum forage production occurred on GA treated plants at
the high rate of chemical application.
Leaflet to stem-petiole ratios were significantly
affected (P = .05) by chemical application (Table 5).
Alfalfa plants treated with GA had a lower leaflet to
stem-petiole ratio than any of the other chemical treat
ments or the control. The lowest ratio was found with
plants treated at the high rate of GA.
All chcmicals tested did not influence the number
of nodes per stem, number of stems per plant, or transpired
water. Plants sprayed wit h GA had longer stems (35 cm)
compared to untreated plants (23*3 cm).
Water-use efficiency was negatively correlated
(P = .01) with total forage, leaflet weight, and stem-
petiole weights. The r values were -0.5$, -0.'l2, and
-0.68, respectively.
The results of this study indicated that GA
affected the .metabolism of alfalfa which was manifested in
an increased plant height and total forage. Increased
forage production was due primarily to an increase in the
amount of stem-petiole tissue produced. Transpired water
was not affected by chemical treatments; therefore, water
requirement was influenced by the significant effect of
these chcmicals on dry forage production.
Table 5- Effect of various chemicals on total forage per plant and leaflet to stem-petiole ratio of Mesa-Sirsa alfalfa grown in a greenhouse environment.
Rat e
Chemic al
Rat e CCC GA IAA DSA PMA Control Mean
Total forage.
Low 1.55* 1.27 1.53 1.35 1.29 1.21 1-37 a ab abc ab abc abc be
High . -99 1.72 1.03 1.02 1.15 1.16 1.18 b c a c c be be
1.27 a 1.49 a 1.28 a 1.19 a 1.22 a 1.19 a
Leaflet to stem-petiole ratio
Low- •95 • 7^ •9^ • 93 .81 •99 .89 a abc cd abc abc bed ab •
High • 99 • 70 1.01 1.06 .96 •96 • 95 a ab d ab ab abc abc
• 97 a .72 b • 97 a 1.00 a .88 a . 97 a
*Values -within rates and means followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
30
Jndoleacetic acid had no significant effect on any
of the characteristics measured except a slight increase
was found in stein height. These results arc: not in agree
ment ivitli those of other investigators ( 'j0 , 70) . The
antitranspirant (DSA) caused severe leaf burn when sprayed
on alfalfa. Since these chemicals proved ineffectual in
the improvement of water use, IAA, and DSA were not used in
subsequent experiments.
Gibberellic acid, PMA, and CCC had significant
effects on water requirement, total forage, and stem-
petiole weight when a1fa1fa plants were grown in an open
environment (Table 6). The lowest water-use efficiency
values were found with plants treated with GA and the
highest values were found on plants treated with PMA and
CCC. The range in values varied from 173^ to 2^0k for GA
and PMA treated plants, respectively. Water-use efficiency
values in the experiment indicated a strong influence of
the environment on this characteristic. Briggs and Shantz
(9) reported differences in water requirement because of
different environmental conditions.
Maximum forage and stein-petiole tissue production
occurred on GA-treated plants. Different rates of GA
influenced the amount of stem-petio1e tissue. Minimum
forage production occurred on plants treated with CCC.
Leaflet to stem-petiole ratios, stem height, and
transpired water values are shown in Table 7* The lowest
31
Table 6. Means of water-use efficicucy, total forage, and stem-petiole tissue as affected by various chemicals applied to Mesa-Sirsa alfalfa grown in a lathhouse environment at the Tucson PI ant M a L er i a 1 s C enter .
Treatment * Water-us e efficiency
Total forage r
Stem-petiole weight, g
3 1738 +
e 1 . 47 a • 87 a
4 1751 e 1.23 ab • 75 ab
2 1915 de 1.19 abc .67 be
1 2000 c de 1.17 abc .63 bed
l4 2075 bede 1.1k abed •59 bed
11 20 76 be de .89 cd •50 cd
12 2l6l abed .83 d .46 d
10 2198 abed •92 bed .47 d
7 2227 abed 1 .06 bed .56 bed
13 2284 a b c d • 9;i bed .50 cd
9 CO
DO
CO
abc • 96 bed .49 cd
8 2358 ab c • 95 bed .50 cd
6 2 417 ab 1 .04 bed .54 cd
5 2504 a .92 bed .46 d
*1, 2, 3, anc! 4, 100, 200, 300, 400 mg GA/liter, respectively; 5, 6, 7, and 8, 10-61 10-5, 10-4, 10-3 M PMA , respectively; 0, 10, 11, and 12, 10-'1, 10~~, 1, 2 M CCC , res pec I: i.ve.l y ; 13, .2% Twet'ji 20; 1 h , Water.
Values within each column followed by the same letter are not: sigaJ. I' i.cantly different at the .05 level according to Duncan's Multiple Range Test.
32
Table 7- Means of leaflet to stem-pet.i ole ratd.os, height, and transpired water as affected by various chemicals applied to Mesa-Sirsa alfalfa grown in a lathhouse onvironmcnt at the Tucson Plant Mat erials C ent er .
Treatment *
Lcaf1et to stem-petiole
rat io Height , cm Trans pired water, g
4 .65 +
c 19-8 a 2111 abc
3 • 72 be 17.7 ab 2432 a
2 .81 abc 16 .5 abc 2 234 abc
11 .82 abc 16.6 abc 1799 cd
12 .88 ab 15-7 be 1644 d
1 • 91 ab 16. 4 abc 2273 ab
8 .92 cib 13.5 c 2171 abc
l4 • 97 a 15-3 be 2316 ab
7 • 97 a 13.9 be 2234 abc
10 1.00 a 13-7 c 1895 bed
13 .1.02 a 13.0 c 2019 abed
9 1 .02 a 13.9 be 2094 abc
6 .1 .04 a 14.8 be 2335 ab
5 3. . 0 4 a 13 .1 c 2093 abc
*1, 2, 3, mid 4 , 100, 200, 300, 400 nig GA/liter, respectively; 5, h , 7, and 8, 10 ~ 6 , 10-5 , 10~/j, 10 - 3 M PMA, respectively; Q, 10, II, and .12, 10-'1 , 3.0-2, i, 2 M CCC, respectively; 13, .2% Tween 20; 14, Water.
*f* Values within each c.o.lunm followed by the same
letter are not significantly different at the .05 1 eve3. acconl.ing to Duncan's Mul.tip.l.e Range Test.
33
leaflet to stem-petiole ratio (0 .6 5) was found on. GA-
treated plants. The highest rate of GA increased p.lant
height over the control plants. Plants treated with dif
ferent rates of GA did differ in the amount of water
transpired. The least amount of water was transpired by
plants treated with CCC. However, this was because severe
leaf burn was present on plants sprayed with CCC. In the
previous experiment, CCC was applied as a soil drench and
no visible effects were noted. Plants treated with PMA did
vary from the controls in the amount of water transpired.
This may be due to the length of time in which PMA was
applied to the foliage in the experiment. However, these
results are in agrceinent with the greenhouse study.
Water requirement was associated (P - .01) with
leaflet weight, stem-petiole weight, and total forage. The
r values were -0.55, -0 .76 , and -0.73, respectively. The
significant correlations of dry weight of the total forage
and yie.Ld components with water-use efficiency .indicate
that to select efficient genotypes dry weight production
would be a major selection tool.
None of the chemicals had any effect on the number
of nodes pea" stem, number of stems per plant, or leaflet
weight . Flowering was promoted by GA application.
Tlio results of these experiments indicated that GA
was the only chemical, which improved the water requirement
3 4
of alfalfa without any harmful effects. All other
chemicals either had no effect or caused piant damage.
Growth Chamber Experiments
One of the first objectives of the growth chamber
experiments was to evaluate the carryover effects of GA on
subsequent regrowhli. The int er act ion, treatment by
harvest, showed GA lowered (P = .05) the water requirement
values when calculated from stem-petiole and total forage
weights (Table 0). No effect was found on water require
ment of each group when averaged over five harvest periods
when the values were computed on yield components or total
forage production. The water requirement values based on
leaflet weights were not significantly affected by GA
treatment.
Gibberellic acid had significant effects on yield
components and total forage of alfalfa (Table 9)• A
significant interaction (P = .05) indicated a positive
response in the amount of forage produced by each group of
plants during the harvest in which they received GA
application.
Transpired water, leaflet to stem-petiole ratios,
and stem height were affected by GA application (Table 10).
More water was transpired by the group of" plants which was
treated with GA. During the throe growth periods when
35
Table 8. Effect of GA on water requirement values of alfalfa based on yield components and total forage for five harvests in a controlled environment.
11 ar vest 1 J. c:UJ. U Group 1 2 3 4 5 M e an
S t em — petiol a*
1 + 1298 . + + b 1193 a 1254 a 1409 b 1354 a 1302 a
2 1121 a 1570 b 1248 a 1229 a i46o a 1325 a
Leaflet
1 1844 a 2020 a 180 3 a 2143 a 2188 a 2000 a
2 1676 a 2079 a 1685 a 1902 a 2099 a 1888 a
Total f or ag e
1 757 b 752 a 736 a 846 b 833 a 785 a
2 669 a 858 b 711 a 74O ci 856 a 767 a
*Values between groups within each harvest followed by the same letter arc not significantly different at the .05 level according to Duncan's Multiple Range Test.
Group 1 treated 2nd harvest Group 2 treated 'id' harvest
Each value is a mean of 12 observations.
36
Table 9* Effect of GA on dry weight of stem-petiole, leaflet, and total forage production of alfalfa for five harvests in a controlled environment.
Harvest j.-' .1. an L Gro up 1 2 3 4 5 Mean
Stem-- it e t .i 0.1 e , K *
i+ 2 . 11 ++ a 2.73 b 3. 46 a 3 .48 a 2 .02 a 2.76 a
2 2 .30 a 1 .83 a 3.72 a 4 . 26 b 2 • 05 a 2.83 a
Leaflet ,, g
1 1 .50 a 1.64 b 2.4l a 2 .29 a 1 .27 a 1.82 a
2 1 . 5 3 a 1 -39
Toti
a
-11
2.6L b
forage, ,1
2 • 75 b 1 .41 a 1 .94 a
1 3 . 61 a 4.3 4 b 5-87 a 5 • 77 a 3 .29 a 4.57 a
2 3 .83 a 3-59 a 6.33 a 7 .01 b 3 .46 a 4.85 a
*Values between groups within each harvest followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
Ciroup 1 treated 2nd harvest Group 2 treated 'it!) harvest
-J* "t* ̂Each value is a mean of .12 observations.
37
Table 10. Effect of GA on transpired water, leaflet to stem~pet:i. ole ratios, and height of alfalfa for five harvests in a controlled environment.
PI ant Group
H arvest
1 4 5 M e an
1
2
2663 a
25'±3 a
+ + l'r nn s | >ir ed wa t er . * .0;
3225 b 4228 a 4-601 a 2701 a 3500 a
2852 a 4343 a 5.I.15 b 2936 a 3558 a
1
2
Leaflet to stem-petiole ratio •
.72 b .60 a .71 a .66 a .62 a .66 a
.67 a .76 b .74 a .66 a .70 b .71 a
.1
2
'17.8 a
4-9.0 a
Height , 0.111
53.2 b 51.0 a 59-3 a 57.4 a
43.9 49.3 cl
53.7 a
62.3 a 55-4 a 52.0 a
*Valu.es between groups within each harvest followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
+Group 1 treated 2nd harvest Group 2 treated 4 <>' liar vest
Each value is a mean of 12 observations.
38
neither group was treated no difference in the amount of
transpired water was found.
The effect of GA on the leaflet to stem-petiole
ratios was not consistent. Differences were found for
harvest 1, 2, and 5• Stem height was increased only on
the second harvest by GA.
Gibbcrellic acid did not appear to have any
influence on any variable measured on the plants during the
harvest following GA application except on leaflet weight
in the third harvest and leaflet to stem-petiole ratio in
the fifth harvest.
Gibbcrellic acid hiuJ no significant effect on
protein percentage of either the leaflet o3.~ stem-petiole
tissue. However, total protein, was increased in the
plants treated with GA and followed the same pattern as
the dry weight changes in each harvest.
Tli e .results of th es-e experiments indicated that the
response of alfalfa to GA treatments was similar to numerous
other species. Increased stem and leaf]et dry weights have
been reported with bean (2). Evtushenko (20) reported GA
was not transferred from one stem to another o11. the same
plant and response was limited to growing parts above the
level of application . Add.i. tiomtlly no carryover effect
was found. Lovell and Booth (36) found no change in the
number of nodes per stem in potato (Sol.anuin tuberosum L.) .
The length of individual internodes was affected by
GA (Fig. 3)» Most of the internodes increased in total
length which result,ed in the increased plant height rather
than more nodes per stem. The largest differences in
internode length were found nearest the base of the stem.
This agrees with Bachelard 's (h) results in. Eucalyptus
c am a 1 d u I. o i1 s 1 s Delia. He reported differences in internode
length depending on the location on the stem and time of
GA treatment. Moore (43) found similar results in the
'Alaska' pea.
Stem length was increased by GA treatment (Fig. k).
Larger differences in stem length were found between the
treated and control, plants as the plants reached maturity.
Different rates of stem elongation were found when alfalfa
plants were sprayed with GA (Fig. 5)- Plants treated with
GA showed a faster rate of elongation h- days eifter spray
ing. Gibberellic acid was applied on the 7th and 1.1th day
following cutoff. The increase .in stein length occurred at
different rates depending on time of measurement and GA
application. Moore (^3) reported there wore periods wrhen
peas were more sensitive to GA application. The response
of alfalfa to GA app ears to be mediated by time.
The data for cell lengths and the number of xylem
cells per vascular bundle are shown in Table 11. in
general, plants treated with GA had longer pith cells.
However, some genotypes did not respond to GA application.
KEY: • A = TREATED A = CONTROL
CI
O o
CD
o 'S3
o
c
1 2 3 4 S 5 7 S S 10
INTERNODE LOCATION
Fig. 3- Effect of GA on length of individual internodes of alfalfa grown in a controlled environment. Internodes are numbered consecutively from cutoff level (one) to stein tip (ten). «£-
6
KEY : © = TRERTED a= CONTROL
DAYS RFTER CUTOFF
F i g . k . Effect of GA oil height of alfalfa steins grown in a control.led environment .
KEY: Q= TREATED a= CONTROL
DAYS RFTER CUTOFF
Fig. 5 . Effoc.t of GA on the rate of stem elongation in alfalfa grown in a controlled environment.
'i3
Table 11. Effect of 01A on the anatomy of alfalfa st ems.
Plant group
Internode Plant group 1 + 2 3 k Mean
Pith cell length, 111111
Treated . 3 8 a* .36 a .29 a .30 a •33 a
Control • 35 a . 30 a •32 a .25 a . 31 a
No. of xylem cells per vascular bundle
Tre exted 23.9 a 22.0 a 20.0 a 17-6 a 20.9 a
Control 22.7 a 21.1 a 19-0 a 16.2 a v.0 CO
*Vc»Iues between groups within each internode followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test.
Base of plant.
kh
The longest colls were located in the internodes (l and 2,
Tabic 11) nearest the basal end of the stem and decreased
toward the stem apex. The results of cell length and
inter node length suggest, that cell elongation was primarily
responsible for the increased length. Bos track and
Struekmeyer (7) reported that GA application caused cell
elongation and a smaller stem diameter in various plant
species. Earlier, these investigators had reported
similar results for soybeans (6).
Essentially no d i ff e r e n c e s were found in the
number of xylein cells between the treated and control
plants. Morey and Cronshaw (kh) found that GA had no
effect on the amount of secondary xylem in Acer rubrum and
GA stimulated cambial activity in localized regions of the
stem.
Effect of GA on Transpiration
Transpiration rates were not constant for two
clones of alfalfa (Fig. 6). M aximum rates occurred during
the first hour following the dark period. The rates
declined during the day as soil moisture tensions
increased. The plants were rewatered at ]. 700 hr. During
the period between 1700 and 2000 hi- transpiration rates
increased because of the lower soil moisture tensions. A
rapid decline occurred during the period between 2000 and
2300 hr. Differences (P - .05) between the clones occurred
KEY: 0 =CLONE 1 a = CLONE 2
TIME (HOURS3
F ig. 6. Transpiration rates for two clones of Mesa-Sirsa alfalfa grown in a controlled environment.
4-6
at 1100, I'lOO, 1700, and 2300 hr . No differences were
found during the dark period. Transpiration rates between
clones were larger1 when 30-55/" of the available soil
moisture was utilized. Selection of alfalfa genotypes
which have low transpiration rates should be done at low
soil moisture levels. However, the difference found in
these clones may not be sufficient to detect under field
conditions.
The rates reported by Al-Kawaz (1) arc lower than
those of the present study. Ehrler (.17) showed differences
in the amount of water absorbed as the saturation deficit
changed. Therefore, difference between the reported rates
can probably be attributed to the different environments.
Gibberellic acid affected the transpiration rates
of alfalfa (Fig. 7)- I", general, higher rates were found
on plants treated with GA. Higher transpiration rates have
been reported in tomato and beans when treated with GA
(15, '16). However, Luke and Freeman (3$) found no effect
of GA on transpiration in oats (Avena sativa L.) .
Each clone responded differently to GA application
(Fig. 8). Clone 2 showed a larger increase in the trans
piration rates with GA treatment than did Clone 1. These
experiments were conducted over a 2-day period and Clone 2
responded similarly both days. However, Clone 1 showed a
decrease the first flay and cin increase the second day,
which caused a significant day by clone interaction.
KEY: 0 =CONTROL A = TREATED O C7
O c
c
CM CTJ
o
o o
2330
TIME (HOURS)
Fig. (. Effect of GA on the transpiration rates of Mesa-Sirsa alfalfa grown in a controlled environment.
t
CNTRL-CLN2
TIME (HOURS)
Fig. 8. Effect of GA on the transpiration rates of two clones of Mesa-Sirsa alfalfa grora in a controlled environment.
CO
iL 9
(P = .05). A summary of the analyses of variance for each
time period is shown in Table 12. The experiment was
repeated with the same clones and similar results were
found.
Data for several characteristics, measured on two
clones used in the transpiration experiments, exhibited
variable responses to GA treatment (Table 13)« No differ
ences were found in several of the characteristics
measured. This was expected because GA was applied only 2
days prior to harvest. However, differences were found in
the photosynthetic rates. A significant clone by treatment
interaction was found. This interaction was evident
whether the data were expressed on a leaf area or leaf
weight basis. The highest rate of photosynthesis was found
in Clone 2 treated with GA. Clone 1 and Clone 2 showed a
decrease and an increase in the photosynthetic rates,
respectively, in response to GA application.
Differences were found in the SLW of the leaves.
The SLW was lower in the treated plants of Clone 1 and no
differences were found in Clone 2.
Effect of GA on Photosynthesis and Respiration
Effects of GA on several parameters measured on
Clone 2 of Mesa-Sirsa alfalfa are shown in Figs. 9 to .1 lL.
Significant differences for all characteristics except SLW
and photosynthesis were found among harvests (Table .1 k) .
Tabl e .1.2. Analyses of variance for the transpiration data, wat or per cm" per hr, measured on Mesa-Sirsa alfal fa in a program controlled environment .
50
Time
Components 0700 OFLOO 1100 I'JOO 1700 2000 2300
Clone ns ns * * * * * ns **
Treatment ns ns ns * * ns ns ns
Clone by treatment ns ns ns ns ns ns ns
Day lis * * ns ** :|; * ns ns
Day by clone ns * ns ns ns ns ns
Day by treatment ns ns ns * ns ns ns
Day by clone by treatment lis ns ns ns ns lis ns
ns Not significant.
* S i gn .1 f i c ant .05 level.
* * Si gni f :i c ant .01 1 evel .
Table 13 • Effect of GA on several characteristics measured on two clones of Mesa-Sirsa alfalfa grown in a program controlled environment.
Clone 1 Clone 2
Characteristics Control Treated Control Treated
Stem-petiole weight, g Leaflet weight, g Total forage, g Transpired water, g Water requirement Leaflet to stem-petiole ratio Per cent moisture Apparent photosynthesis' Apparent photosynthesis + +
Specific leaf weight, mg/cm Leaf nrea. cm-
2 .02 a* 1 .88 a 1 .88 a 1 .76 a 1 .13 a .90 a 1 .02 a .88 a 3 .15 a 2 .78 a 2 .90 a O .64 a
1279 s. 109'5 a 1567 a 1312 a 395 b 384 b 539 a 496 a
.56 a .48 b . 5 'i ab . 50 ab 80 . 1 a 81 . 8 a 80 . 8 a 80 . 1 a 8i . 7 b 79 .1 b 90 . 9 ab 100 . 7 a 35 .1 a 27 .8 b 29 . 7 ab 35 .2 a k • 3 a n J . 6 b 3 • 3 b 3 • 5 b
260 a 253 a 309 a 250 a
*Values within characteristics followed by the same letter are not significantly different at the .05 level according to Duncan's Multiple Range Test. Each value is a mean of five observations.
' mg C0o g hr
mg C0r> dm " hr
Kb f o = i Rc.R i c.0 * = CONTROL
rw p To •—r o
UJ y UJ al
LU O a:
i cr
CONiROL RESTED
10 K
DRYS RFTER CUTOFF DRYS RFTER CUTOFF
Fig. 9* Effect of GA on the percentage moisture and total forage of Mesa-Sirsa alfalfa grown in a controlled environment.
cc
KEY: © = TRERTED * = CONTROL KEY: 0= TRERTED ^ = CQNTRO'
!
C)
LiJ
CE LJ
1 14
DRYS RFTER CUTCF DRYS RFTER CUTOFF
Effect cf G.A on the s'ceni-peticle and leaflet weights of Mesa-Sirsa alfalfa grov.'n in a controlled environment .
i
KEY: e = TRERTED a =CONTROL KEY : o =TREATED A =CONTROL
! i J cr: ZD o i;J
OC L'J ! -o: ~j I
DRY-S RFTER CUTOFF GRYS RFTER CUTOFF
11. Effecl of GA on transpired vrater and water requirement of Mesa-Sirsa alfalfa grovrn in a controlled environment .
\JI
KEY: o = IRERIED ^ = CONTROL KEY: o=TREATED a = CONTROL
C3 00
cb
to
1^ 10
1 14
DRYS fiFTER CUTOFF DRYS RFTER CUTOFF
Effect of GA on leaflet to stem-petiole ratio and specific of Wcsa-Sirsa alfalfa grown in a controlled environment.
leaf weight
KEY: o = TRERTED a = CONTROL KEY: o=TRERTED a = CONTROL
o
cn ai i—i Q_ CO UJ
O
CE C£ i—i Q-CO UJ CC
DRYS RFTER CUTOFF DRYS RFTER CUTOFF
Fig. 13' Effect of GA on respiration rates of Mesa Sirsa alfalfa grown in a controlled environment. Left) mg CC>2 dm~2 hr~l. Right) mg CC>2 g-1 hr~l
ui C7\
KEY: o= TREATED a = CONTROL KEY: o = TRERTED ^ = CONTROL <s
CO
o CJ
CO LU x: o
CM ~ CO I— ^— CO o I— o 32 Q_ o
o
10 14 6
o
CO
o
CO i—i
o CO UJ 31 CO I— >-CO o I— o O 32 Q_
LO
O d
DAYS AFTER CUTOFF , DAYS AFTER CUTOFF
Fig. l4. Effect of GA on photosynthetic rates of Mesa-Sirsa alfalfa grown in a controlled environment. Left) mg CO dm-^ hr~l. Right) rag C0o g~l hr~l.
u Z
VJ1
Table 1 . Summary of the analyses of variance for testing the effect of GA on various characteristics measured on Clone 2 of Mesa-Sirsa alfalfa in a controlled environment.
Characteristic Treatment Harvest Treatment by harvest
Fresh weight, g * * * ns Transpired water, g ns * 11 s Stem-petiole weight, g * *
Leaflet weight, g ns * * ns Total forage, g ns * * 11s V."ater-use efficiency * *
Leaflet to stem-petiole ratio ns * * ns Specific leaf weight, mg/cm^ ns * *
Per cent moisture lis * * ns Respiration, mg CO2 dm-^ hr~l ns * * ns Photosynthesis, mg CO2 dm~2 hr*"l ns ns ns Respiration, mg CO2 g~hr-1 ns * * ns Photosynthesis, mg CO2 hr-1 ns ns ns
ns Not significant.
*•05 level of significance.
**.01 level of significance.
59
The data for total forage, each component of yield, and
transpired water show an approximate linear increase with
maturity. The plants Avere in the bud stage of development
at the final harvest. The plants treated with GA had a
higher percentage moisture and the difference became larger
with .increased plant age (Fig. 9)» Shchulcina (55) found a
lower percentage moisture in the leaves of alfalfa when
treated with GA.
Water requirement values for the treated plants
remained constant over time compared to the increase in
nontreated plants (Fig. 11). The reduction in water
requirement was primarily due to increased stein-petiole
production with no difference in the amount of water
transpired or leaflet production. The leaflet to stem-
petiole ratio of the treated propagules was not signifi
cantly lower than the control; however, the trend was a
lower ratio in the treated plants.
Differences were found in the SLW between treated
and control plants and the effect became larger with time
(Fig. 12). The SLW was always lower for the treated
plants. Pearce et al . (52) reported that the SLW A^aried
with leaf age and was influenced by light intensity. They
reported SLW values varied from 1.9 to 5«5« The SLW
values of this experiment varied from 2.0 to 2.9.
Respiration differed among harvests whether the
data were expressed on leaf area or leaf weight basis
6o
(Fig. 13). The same gcnural pattern was evident in both
methods of data expression, with the control plants lower
.in the second and thi.rd harvests . Respiration values
- 2 - L varied from 1.0 to 3*1 CO0 din hi" " . These values
C-t
compare to those reported by Al-Kawaz (.!)•
Photosynthctic rates were always lower on plants
treated with GA when the data were expressed on a unit of
leaf area (Fig. 14) . However, whan the d at a were expressed
on leaf weight the control plants were lower in the second
and third harvests. These results can be attributed to a
decrease in the SLW of the treated plants. The same leaf
area of the treated plants did not weigh the same as that
of nontrcated plants. Therefore, on a weight basis there
were more leaves per gram in the treated piciiits .
Coulombe and Paquin (15) indicated that GA influ
enced the rate of respiration and photosynthesis of
tomato. They reported the maximum effect resulting from
GA application was 5 hr after treatment and then the rates
began to decline to normal. The measurements on alfalfa
wore in a d e approximately 9 hr after treatment; therefore,
maximum response may not have been found in this study.
The percentages of each carbohydrate fraction and
crude protein of the roots were affected by GA (Table 15) •
The .amount of free sugars and the ncid-hydi'olyzoble frac
tion were reduced by 1 ') . (t and 3f5.8%, res pec Lively . A
slight, increase was found in pro (. e in con Lent. Love 11 and
6i
Table IfJ. Effect ol" GA on c arbohydrat e fractions and protein content of roots from Clone 2 of Mesa-Sirsa alfalfa grown in a controlled environment .
Carbohydrate fractions, %
Plant 80% O 0/ <i/o Protein g.r 0 u p ethanol H2S04
percentage
Treated 12.0 b:i 17.6 b 9.5 a
Control 1 4. 7 a 28.4 a 9-0 a
% of control. 8.1 .4 62.2 105-9
*Values between treatments for each parameter followed 'by the same letter are not significant at the .05 level according to Duncan's Multiple Range Test.
Yi o o t h (36) f o und a reduction in the amount of ethanol
soluble carbohydrates in potatoes when treated with GA.
The results of this study suggest the increase in
stem-petiole tissue was because the root reserves were not
replenished. Previous work und or irrigated conditions in
Arizona lias shown that starch was the major storage compound
in alfalfa roots (lG). Weaver, Shindy, and Kl;i. ewer (G 7)
showed GA had a sign ificant inf luence on translocation of
organic acids in grapes . Other research ( 4 , 36, >15) has
shown GA influenced the amount of starch stored in various
plant organs. The photosynthetic products were probably
not trnjis.l ocatod to the roots and were used to increase the
dry weight of the stem-petiole tissue in alfalfa.
62
F j. e 1 d Exp ei":i.inon t s
Gibberel.l.ic acid (15G nig/I it er) was sprayed three
times in. the f i.e 'l d at 4 day iiitcrva I s beginning who 11 the
regrovth was approxiniately G cm. Gibbercllic acid signifi-
cantly affccted CI.VA,' forage accumulation under .field condi
tions (Fig. 15)• Plants which were sprayed with GA
produced more forage (P = .05) than did the control plants.
A rapid increase was noted during the first three harvests.
Significant differences in forage yields at the bud and
early bloom stage of plant development for each harvest
were found for plants sprayed with GA (Table l6). The
treated plants yielded more forage than the nontreated
plants (P = .05)- However, regrowth was reduced by GA
treatment.
The effect of GA on components of yield and leaflet
to stem-petiole ratios was also evaluated under field
conditions (Table 17)• In general, primary and secondary
stem weights were greater on the alfalfa plants sprayed
with GA. The total amount of leaf tissue was not influ
enced in either harvest by GA treatment. The leaflet to
stem-petiole ratios were lower on the treated plants in
both harvests because of an increase in stem weight. The
treated and nontreated plants in Pig. 16 illustrate the
effects of GA on stem height and secondary branching of
alfalfa plants grown under field conditions. The effect of
63
a = CONTROL KEY s o= TRERTED
DRYS RFTER CUTOFF
Fig. 15. Effect of GA on the yield of Mes^-Sirsn alfalfa crown under field conditions. Data "taken from an o area ot .19 in".
64
Table .1.6. Effect of GA on yield of Mes a-Sirs a alfalfa grown under field conditions at Tucson, Arizona for two harvest periods in 1970.
Dry forage production (g/plot)
Harvest Treated Control Regrowth p c r i o d g S 1st treat, ed
May 28 67-5 a* 56.7 b - -
June 22 78.5 a 50-9 b 33.1 c
* Veil ues followed by the same letter within a harvest period ore not significantly different according to Duncan's Multiple Range Test. Mean based on 3 samples collected from an area of .19 "i" (2 ft 2) .
Table 1 7 - Effect of GA on yield components and leaflet to stem-petiole ratios of Mesa-Sirsa alfalfa grora under field conditions.
Primary Primary- S econdary Secondary Total Total Total Harvest Treatment s t ems leaves s t ems 1 e a v e s s t ems 1 eaves forage
Components viol d rr
Treated 8.78 a* 2 . 20 a 2.05 a 2 . 31 a 10.83 a 4.51 a 15-33 a May 28
Control 6.14 b 2 . 34 a .83 a 1.71 a 6.97 a 4.05 a 11.01 a
Treated 7.07 a 1. 30 a 2 . 40 a 1 .81 a 8.37 a 4.21 a 12.58 a June 22
Control 5.08 b .52 b 2.26 a 1-37 b 5 .60 b 3.63 a 9.23 b
Leaflet to stem-p etio1e ratio
Primary- •Secondary- Total axis axis pi ant
Treated .25 b 1 .14 a .41 b May 28
Control .38 a 2.15 a .58 a
Treated .34 b 1-39 b • 50 b June 22
Control .44 b 2.26 a .65 a
* Values between treatments are not significantly different at Range Test.
for the
each parameter followed by the same letter .05 level according to Duncan's Multiple
H • •u HB
Em
•1
66
Fig. l6. Effect of GA on stem length and secondary branching. l) Control. 2) Treated.
67
GA on these parameters was also evident in the growth
chamber studies.
The amount of water utilized by the treated and
nontreated plants was not influenced by GA application.
Significant differences were found in the amount of water
absorbed at different soil depths over the period of the
study. However, no harvest by soil depth-level interaction
was found. Therefore, the plants which were sprayed with
GA had a lower water requirement based on forage produc
tion .
Anatomical measurements on stems and leaves of
alfalfa indicated GA influenced these parameters (Table
l8). Data from the field experiments agree with the
growth-chamber experiments. Increases in the parenchyma
cell length were evident in the central pith. Also,
individual internodc lengths were comparable to the previ
ous results shown in Fig. J. Leaflets were thicker 011
treated plants near the base of the stem. Spraying with
GA affected other anatomical features of alfalfa leaves
(Fig. 17)• Intercellular spaces were more abundant in the
treated leaves. Also, the mesopliyll cells were elongated
and less densely arranged. No effect was evident in the
central midvein. Bostraclc and Struckmeyer (6) reported
more intercellular spaces and a smaller palisade layer in
treated soybean leaves.
68
Tabic l8. Effect of GA on the anatomy of Mesa-Sirsa alfalfa leaves and stems.
Int ernod e from base
Pith c: ell length, mm Leaf th.i ickiiess , 111111 Int ernod e from base Tro a10 d C011.tr 101 Treated Control
k .3 yJ a * .29 a .26 a .21 b
7 .32 a .18 a . 20 a .19 a
ap ex — • l6 a .16 a
* V a I u e s between t r c a t monts v i t h in a n in t e mode location followed by the same letter axe not significantly different at the .05 level according to Duncan's Multiple Range Test.
69
Fig. 1 7 . Effect of GA on alfalfa leaf anatomy. Note the increased width and the arrangement of palisade and spongy mesophyll cells (1250 X). Upper) Treated. Lower) Control.
70
Application of CVA definitely inriuenced raceme and
flower development (Fig. -1.8) , No quantitative measurements
were made, but it was evident by visual observation that GA
promoted eaivl lor I:'Ioweriii.g and elongated the flower racemes.
Also, the sepal s were elongated and were curled ne ar the
apex. iS'o differences were evident in flower color.
The effect of GA on photosynthesis, respiration,
and SLW of alfalfa grown under field corulj Lions was investi
gated (figs. 19, 20, and 21) . Plants treat0d with GA
exhibited lower va.'Laes in. all parameters over most of the
growing period . Differences (P •- .05) between harvests
were found in all characteristics. The results agree with
those obtained in growth chamber studies. The photo-
synthetic and respiration, rates were very similar between
environments except, for the first harvest in the field
where higher rates were found. The high rates were
probably the result of age of the leaves. Previous
research had j.ndic irt ed a decrease in photosyn the tic rates
as 1 ea ves 111 atur ed ( 5 L ) •
The increase in al 1 parameters at the sixth harvest
is d i fficul t (0 explain . The tec.hui.que used in this study
for pliot os yn the tic measurements allowed use of only the
upper 25 to 28 cm of the stem. At; the time of the sixth
harvest, secondary Loaf development was prominent from the
axillary buds located in the; region used for measurement .
Effect of GA on raceme and sepal elongation, l) Control. 2) Treated.
KEY: o = TREATED * = CONTROL o
to
o
o cn CNJ to i—i
to UJ x I—
o cn
t— O X 0-
o LO
D O
24 12 18 22 16 14
DAYS RFTER CUTOFF
_ n Fig. 1 9 . Effect of OA on photosynthesis (mg COo dm *" lir
of alfalfa grown under field conditions.
K E Y : © = T R E A T E D * = C O N T R O L
Csl -J-
P? -cn
_
D
O T 22 12
i 14
i IB 18
I 20 24
DRYS RFTER CUTOFF
- 2 Fig. 20. Effect of GA on respiration (mg COo dm hr
of a] fa] fa grown under field cond i Lions .
7'J
KEY: o= TREfiTED a= CONTROL
DRYS RFTER CUTOFF
Fig. 21. Effect of GA on .specific .Loaf weight (SLW) alfalfa grown under fic.l d conditions.
of
75
The increased number of young leaves may have accounted
for the increased rates.
Respiration and photosynthesis ineasuremouts compni'e
favorably with values reported in the literature for
alfalfa (.1.8, 51). Previous research lias shown that GA
influenced the NAR of beans and wheat (2, 29) . However, a
species response was noted with a decrea.se in wheat and an
increase in beans. IlaJevy, Monsc.l ise, and I'.l.aut (28)
showed a decrease in the di~y matter content of leaves and
attributed the reduction, to increased translocation. The
lower SLW may have resulted from an increased translocation
in alfalfa.
Chlorosis on the treated plots was evident in the
field (Fig-. 22). Chlorosis .in other species treated with
GA has been reported by several researchers (5, 6, ̂ J2, 66).
Reductions in chlorophyll content were found for mono-
cotyledonous and dieotyj edonous species (66). Larger
differences were evident in the chlorophyll 13 content of
primary leaves with little variation in the secondary
leaves (Table 19)• Ismail, Biggs, and Oberbacher (30)
found that GA delayed ch.l orophyl I degradation in detached
oranges ( C.i. I.rus s [ n ens is Blanco) ; however , a cu.'l tivar
response was evident. Results with other legume species ,
peas and vetch, have shown a decrease .in chlorophyll
content (66). A spectrophoLometric trace of a chlorophyll
Chlorosis and increased height of Mesa-Sirsa alfalfa following GA application under field conditions.
Table 19- Effect of GA on chlorophyll content of primary and secondary leaves of Mesa-Sirsa alfalfa.
Leaf type Treatment
C h1or o phy11 A
mg/g F.W,
Chlorophvll B
mg/g F.lv.
Total Chlorophyll mg/g F . \v.
% Chlorophyll
A'
Primary Treat cd
Control
1.20 a'
1.32 a
, 30 b
.8^1 a
1.50 b
2.16 a
80.0 a
61.1 b
S econdarv Treated
Control
1 .20 a
1 . 32 a
.30 a
. 36 a
1 .50 a
I.56 a
80.0 a
8 k . 6 a
letter ar Multiple
Values between treatments within e not significantly different at Range Test.
each parameter the .05 level
' followed by according to
the same Dune an's
7'6
extract indicated that GA a I' fee ted the transmi t1 anc e of
.light at all wavelengths between 4 00 and 700 ni]i. (Fig. 23).
'Jiie effect o C GA on c arbohydrnt e fractions and
percentage: prott:.i.n of field grown alfalfa rooty v,7ere
measured (Table 20). The results of the field experiments
agree with the growth chamber studies. A reduction in each
carbohydrate fraction was evident in both harvests. The
regrowth of the plants treated with GA in the first harvest
was intermediate in. the acid-hydros,able carbohydrate
fraction at the end of the second regrowth period. These
data indicate that starch storage was delayed only for the
first harvest and GA had ny influence on subsequent trans
location . Percentage protein showed a slight increase in.
the treated plants.
Qualitative determinations of the free sugar
extract indicated that only sucrose was present (Fig. 2fl) .
Dobrenz (.1.6) indicated that sucro.se wets the major component
of the free sugars; however, glucose and fructose were
present in small quantities. In the present study,
sample preparation and a different c.ultivar may have
accounted for the absence of glucose and fructose. Lee
and Rosa (3'0 found a reduction of starch in tobacco
leaves treated with (iA . Other- researchers ( 3 , 'l 5 ) showed
that starch metabolism was affec.ted and more sucrose was
present in. trc?aled corn leaves (50).
79
100 /-1—' 700
Fig. 23* Effect of GA on per chlorophyll extract
cent transniittance of a of Mesa-Sirsa alfalfa.
Table 20. Effect of GA on carbohydrate fractions and protein content of roots of field grora .Mesa-Sirsa alfalfa.
Carbohydrate fractions, %
Harvest Treatment
U fV / uU/0 ethanol "2-50/,
Protein oercent age
Mav 28
Treated
Control
% of control
9 • !i a:
11.1 a
8^.9
6.0 b
18.9 a
31-7
l^i.5 a
13.9 a
104.8
June 22
Treat ed
Control
Regrowth
9-5 b
13-6 a
13-9 a
k.7 c
11.0 a
7.9 b
10. Li a
9-5 a
9-5 a
0' of control 69 .9 ZLO 109-6
'Values between treatments for each parameter followed by the same letter are not significantly different at the .05 level according to Duncan's Nultiple Range Test.
8i
Fig. 2k. Photograph showing the separation of free sugars by thin layer chromatography. Standards were prepared at a concentration of 2 mg/ml. Maltose was spotted with 10 and 25 [il , and M2 , respectively. Sucrose (S) and fructose (F) were spotted with 25 JJ,1 and the unknown was spotted with 5, 10, 25, and 50 |j,l, la, lb, lc , and Id, respectively.
82
The datct of the field experiment indicate that the
water requirement of alfalfa can be lowered by increasing
dry forage production. Under field conditions, GA
increased the total forage produced when applied as an
aqueous spray. However t root reserves were reduced and
regrowth was lower on the subsequent harvest. Therefore,
the application of GA oil a practical basis is not
jus ti Pied.
SUMMARY
Plants of Mo rile a.tco «ativa L . cultxvur Mcsa-Sirs;i
were used to evaluate the offact of various growth regula
tor ami ant i trai"1 s p Iran t chemicals on water-UH e efficiency
and o tli or physiological. , morphological, and anatomical
characteristics . Experimen ts wore conducted in greenhouse,
lathhou.se, growth chamber, and field environments.
Water-use efficiency values were significantly
lower when plants were sprayed with an aqueous solution of
GA , in all environments. However, when other growth
regulator or antitranspirant chemicals were applied no
sign.i r.i.caut effec t was found on water requirement in a
greenhouse environment. The water requirement of alfalfa
was increased when plants were sprayed with PMA and CCC in.
a lathhouse environment.
Gibberellie acid increased total forage production
in all. experiments . The increase was primar 11.y due to more
stem-petiole production with essentially no change in
leaflet production. However, in some experiments secondary
brandling was increased by GA and this resulted in an
increased amount of leaflet tissues.
Gibberellic acid proniot ed early flowering and caused
morphological changes in tin.- flowering raceme . An increase
in pi.th cell length, .'leaf thickness, i.nternodo length, stem
A 3
8'i
height, ,'ind .rate of stem elonga tioji \fas found on plants
sprayed with GA .
The effect of GA on l;raTiP|):i rati on was mediated by
soil moisture comii Lions. When, the soil mo is turo content
was nenr fx old capacity GA did not inl'J uence transpirata.on
rates. However, as the soil 1110 is turo-porccnt age decreased
transpiration rates were significantly increased, Two
alfalfa genotypes responded differently to GA treatment.
- 2 - I Photosynthesis (nig C0r dm " ar ' ) was I ower for plants
treated with GA when .grown under growth chamber and field
environments. The S1. V was .lower on p ."1 ants sprayed with GA;
therefore . when the photosynthesis and respi.ral.ion data
were expressed on a leaf weight: basis, variable results
were found depending on the time of measurenient after
cutoff.
Chlorosis was evident on pi an Is sprayed with GA in
field conditions. The yellowing was primarily caused by a
reduction in the chlorophyll 1! content, of primary leaves.
Also, all fractions of the chlorophyll extract were lowered
in both primary and secondary leaves.
Plants treated with GA had a .1 owor percentage of
free and acid-hydro.l. yzable carbohydrates in the roots.
This effect was found in both greenhouse and field environ
ments. No qual i t at :i. v e effect was found on the free sugars
extracted wj th 8()"'i < - than "> I . Sucrose was the only sugar
I) r e s e 111 in t h e e x L r a c t .
85
Percentage protein of the roots showed a slight
inc.rea.se when the plants were sprayed with GA. However, no
effect on protein percentage was evident in the above
ground forage when the plants were treated with GA.
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