Senna Salt Stress

8/10/2019 Senna Salt Stress

1/9

Journal

of

Experimental Botany, Vol. 28, No. 103, pp. 4 84-492, April 1977

Some Primary Featuresof Salt Tolerancein Senna

Cassia acutifolia)

ALI T. AYOUB

Hudeiba

Research

Station, P.O. Box

31,

Ed-Damer, Sudan

Received 1March1976

A B S T R A C T

Studies

on the

germination

of

Cassia acutifolia (senna) seeds indicated that they were highly

tolera nt of salinities up to 160 m mhos cm

1

, and50per cent reduction in germination occu rred

at about 20-0 mmhos cm

1

.Airtemperaturehad a significant effect onsenna germinationat

substrate salinities between 10-0and25-0 mm hos cm

1

.

Seedling growth was more sensitivetosalinityandalkalinity tha nthegermination stage.

Yo ung pla nt surv ival an d tota l pod yield were significantly reduced insoilsalinities higher th an

11-0 minhoa cm

1

, an d this was more pronounced when plan ts were irrigatedatshort intervals

with salinewaters.The sensitivity of senna to higher levels of salinities was correlated with the

higher rate of chloride accum ulation in the tissue resulting in specific chloride injury. However,

the possibilityofsodium injury cannot be excluded.

I N T R O D U C T I O N

In a previous paper (Ayoub, 1975), the importance of senna Cassia acutifolia)as a

promising irrigated cash crop was put forward. The crop requires high temperatures

and an abundance of sunlight (Gupta, 1971), and these conditions prevail in the

more arid parts of the Sudan where soil salinity and alkalinity problems may be

important. A study was, therefore, undertaken on the effects of salt levels, salt

types, and soil alkalinity on senna germination, vegetative growth, yield, and

mineral composition. Some environmental factors which may effect salt tolerance

by senna, such as watering interval and air temperature, were also included in

these studies. The present paper reports some primary features of these studies.

MATERIALS AND METHODS

Germination

studies

Germ Lnation expe rimen ts were carried out i n 10 -cm-diameter P etri dishes in asinglerandomized

design with 11 levelsof NaCl solutions (0-40-0 mmhos cm

1

) replicated four times.Ineach

sterilized Petr i dish, 10 hea lthy surface-disinfected (HgCla) senna seeds were placed on

a

filter

paper bed, covered with another sheetoffilter paper,andsoaked with 10 mlof the specified

solution. This volume was sufficient to satu ratethefilter papers a ndtopartially immersethe

seeds.ThePe tri dishes were coveredandplacedin thedarkin an incubator maintainedat

30 2

C.

The germination coim t was taken every 24h.

Interaction o f

temperature

an d salinity

on germination

The germination tests were carried out

in

Petri dishes

as

described above. Salt levels used

were 0,5 0, 8-3,

16-3,

24-5,and33-6mmhos cm

1

NaClat25 Cand each testwasreplicated four

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Ayoub Salt

Tolerance

in Senna 485

t imes.

Replicates were incubated at 12-15, 28-30,

3235,

and 40-45

C

and germ ination counts

were made on the 7th day.

ESP tolerancestudies

Hud eiba Research Station Farm he avy claysoil(Vertisols) was air-dried, crushed, a nd sieved

throug h 2 mm mesh. Soils of different exchangeable sodium perce ntage (ESP) levels were pro-

duced following the method of Chang and Dregne (1955). Final ESP levels obtained were

approximately 5, 15, 24, 35, 45, and 55.

These soils were again air-dried, sieved, and 5'5 kg of each soil placed in 21-cm-diameter

plastic pots and randomized on a ventilated greenhouse bench. Each soil test was replicated

five times. Ten seeds of senna were sown in each pot and irrigated when necessary with low-

salt tap water (0-20 mmhos).

Germination counts were recorded and after a period of 30 d plants were harvested for dry

matter determinations.

Effect of

salt

types and

levels on

plant

growth

About 5

5 kg

of washed san dy loam

soil were

put in

60

plastic pots

21 cm

diameter) with drain-

age holes and 10 seeds of senna were sown in each pot. For a period of

2

weeks the pots w ere

irrigated a lternately w ith tap w ater and Hoagland nutrie nt solution after which the seedlings

were thinned to four plants per pot and 45 pots of uniformly growing plants were selected for

salt treatments.

Equal concentrations of NaCl, CaCla, Na2SO4, and an equal mixture of NaCl and CaCl2

were compared at the levels shown in Table 2. Saline waters were applied gradually to allow

for osmotic adjustment until the final specified salt level was maintained. The plants were

harvested after 8 weeks of growth in salt treatm ents and the fresh w eight of the new growth

and its mineral contents were determined. Observations such

as

plan t survival an d leaf shedding

were also taken.

On dry ashed plan t m aterial Na and K were determined by a flame photom eter, Ca and Mg

by titrating with EDTA, and Cl using the AgNOs method (Chapman and Pratt, 1961). Soil

salinity (EC) was measured following the U.S. Salinity Laboratory method (Richards, 1954).

All experiments re ported abo ve were repeated a nd com parable results were o btained.

Frequencyofirrigationwith NaCl onsenna growth

Seeds of senna were planted in metallic lysimeters with drainage holes at the bottom and

containin g ab out 130 kg of river silt. The lysimeters used were oil drum s 65 cm high and 60 cm

in diameter and painted with a sphalt. The experimental design was a factorial combination of

five concentrations of NaCl (0-2, 2-5, 5-0, 10-0, and 20-0 mmhos cm

1

) and two intervals of

watering (every

7

or 14 d with t he salt solution). These lysim eters, with three replicates, were

arranged randomly in the open air where daily tempe ratures ranged between 25 and 39 C.

They were watered w ith ta p w ater whenever necessary until the salt treatm ents were applied.

Just before applying salt treatments the plants were thinned to eight per lysimeter.

Salt was applied after

4

weeks from sowing in increm ents of

2-5

mm hos NaCl in the irrigation

water every other d ay to allow for osmotic adjustm ent until the plan ts were receiving solutions

of assigned concentration. Salt concentrations in the soils at harvest are shown in Table

3

a s

mmhos cm

1

of saturated extract. The volumes of solutions added were sufficient to allow

copious drainage and thorough flushing out of the root medium.

Observations concerning plant survival and development were recorded. Samples of dead

plants were also taken throughout the duration of the experiment. Pod yields were recorded

periodically an d a t the termination of the experiment yield com ponents and

some

plant charac-

ters were determined. Leaf samples were also taken for N a a nd Cl analysis.

R E S U L T S

Effect and NaCl levels on seed germination

Senna seed germination never exceeded 75 per cent and under field conditions the

maximum germination obtainedwasusuallylessthan60per cent. Thislowgermina-

tion percentage is mainly due to the presence of 'hard' seeds which do not imbibe


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486

Ayoub Salt Tolerance in Senna

100-

90

80 -

70-

| 6 0

I 50-

8

I 40

30-

20-

10

0

4 5 6

Days from sowing

FIG. 1. Sen na seed germination at different NaCl levels. The num bers on the g raph are NaCl

solution conductivities in mmhos cm

1

at 25 C.

water even after 10 d soaking. Laboratory tests have indicated that these seeds

have an impermeable seed coat. The da ta shown in Fig. 1, presenting germination

perce ntage in relation t o different salt levels of th e sub stra te, are therefore based on

germinable seeds.

Control seeds completed germination on the 7th day. Seed germination was

satisfactory up to a sa lt level of about 16-0 mm hos cm

1

NaCl. Between salt levels

of 20-0 and 24-0 mm hos c m

1

germination was reduced 50 per cent and beyond th e

salt level of 30-0 mm hos cm

1

germination was almost inhibited.

Interaction of salinity and

temperature

on senna germination

Fig.

2

shows the effect of salinity a t different

ah

temperatures on senna germina-

tion. Su bstr ate salinity, ah- tem pera ture, and their intera ctio n highly significantly

affected senna germ ination . U p to a salinity of6-0mmhos cm

1

the re was no differ-

ence between tem pera tures from 28 to 45 C hi germination percentage. Air tem-

perature had its greatest effect on germination at salinities between 10-0 and 25-0

mmhoa cm

1

. Fifty per cen t reduction in germ ination occurred a t salinities of abou t

10-0,

17 0, and 22-0 mm hos cm

1

when air tempe ratures were 40-4 5,32-3 5, and 28-

30 C, respectively. Senna did not germinate at temperatures below 15 C.

Effect o f ESP levelson sennagerminationandseedling groioth

The data

ha

Table

1

shows th e effect of different E S P levels on senn a seed germina -

tion and seedling growth. Seed germination was satisfactory up to an ESP level of


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Ayovb

Salt Tolerance

in

Senna

487

o o

5-0

1

3

5-0 20-0 25-0

NsCI levd (mmhos cm

1

)

F i o .

2. Effect of NaCl levelsa t different a i rt e m p e r a t u r e s o ns e n n a s e ed g e rm i n a t i o n :

2 8 - 3 0 C ; , 3 2 - 3 5 C ; A A ,4 0 - 4 5C .

350

O

35.

Bey ond t h a t level some seeds germ inated, b ut m ost of the seedlings died sho rtly

after that. Seedlings growing

in

ESP levels

of

25

or

more were stunted

and had

bleached-yellowish (chlorotic) secondary leaves.

The

effect

of

ES P was, there-

fore, m ore pronounced

at

the seedling growth stage than during seed germination.

TABLE 1.Effect of

exchangeable

sodium

percentage

ESP)

onsenna seed

germination

an d

seedling

growth

E S P

5

15

25

35

45

55

Relative

germination (%)

100-0

96-3

88-9

88-9

48-2

33-3

Relative

growth (%)

100-0

6 0 1

45-8

32-8

25-0

1 0 0

Effect of salt types and saltlevels

P lan t grow th, survival, and mineral composition from the different tre atm ent s as

obtained

at

th e end of the

8-week

period of growth are shown in Table

2.

Plants receiving additions

ofC GI2

were affected more markedly than those re-

ceiving the correspondinglevelsof NaCl while plant s grown inNa2SO4media showed

less chan ges

in

growth than those grown in NaCl.


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T A B L E

2. Effect of

equal conductances

o f

different

salt types on senna growth,

survival,

and m ineral composition

Sftlt treatments

Type

mmhoscm

1

ITIM

Relative

growth

Plant

survival

Mineral contents (mBq per 100 g dry wt.)

N a

Mg

C a

Cl

N o

salt

NaCl

CaCla

N a

2

S O

4

CaCla+NaCl

0-2

2-5

5 0

1 0 0

20-0

2-5

5-0

10-0

20-0

2- 5

5- 0

10-0

20-0

10-0

20-0

1-4

22-0

43-9

87 8

175-6

14-6

29 3

58-0

117-2

16-5

33-0

66-0

132-0

73-2

146-4

100

96

66

29

17

100

41

23

12

79

89

61

23

46

2

100

100

88

49

19

100

86

54

14

94

97

85

25

64

25

4-6

4-4

6-9

19-9

38-0

4-5

7-1

3 1

8-2

12-3

14-1

13-6

16-7

19-9

30-1

73-9

67-5

60-9

57-0

42-7

64-5

54-5

52-4

53-2

64-7

63-4

65-2

58-1

49-9

52-4

60-9

44-4

51-0

41-9

38-7

105-3

116-0

120-0

100-3

105-3

83-9

60-0

53-5

46-1

69-9

69-9

87-3

95-8

103-8

124-8

87-3

108-3

112-3

143-7

05-9

60-4

91-3

87-3

128-7

141-2

4- 9

18-2

34-2

106-6

121-2

1 9 0

04-0

94-0

186-0

7-5

7-7

9-5

106-6

107-2

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Ayoub Salt Tolerance

in

Senna 489

There wasaprogressive reduc tioningrowth with increasing salinityofthesub-

strate. This effect

was

more apparent

in the

plants exposed

to

chloride salinity.

Fifty

per

cent reductions

in

growth were found

at 4-0

mmhos

cm

1

CaCl2,

at 7-0

mmhos cm

1

NaCl,

and at

abou t 13-0 mm hos cm

1

Na2 SO4. Da ta

on

leaf shedding

and plant survival confirmed

the

results reported

for

plant growth.

Mineral

compositionofshoots

Mineral contentsof plant shootsas mEq per 100 g dry wt. are also shownin

Table2. The control plants contained very littleNa andC l,but theirK contents

were high. Increasing NaClin thesubs trate increasedCl and Na anddecreasedK

con tents of shoots,

Cl

being accum ulatedatmuch higher rates. Sodium accum ulated

in larger amountsin the shoots from NaCl treatments than from Na2S(>4,and Cl

T A B L E 3. Effectof irrigation frequency with different NaCl levelsonsenna yield

and yieldcomponents

Irrigation interval NaCl levels (mmhos cm-

1

at 25

C

C) of saturated soil Watering

extract effect

0-9 7-5 10-1 16-1 27-8

Pod yield (g/pot)

7d 47-0 52-0 16-1

14 d 18-2 24-3 11-6

Salt effect 32-6 38-2 12-9

S.e. means salt effect = 5-42, watering effect = 3-44.

No. of pods/pot

7 d 661-3 691-3 228-3

14 d 254-7 330-0 176-7

Salt effect 458-0 510-7 202-5


Final plant survival/pot

7 d 8-0 8-0 4-7

14 d 7-7 8-0 8-0

Salt effect 7-9 8-0 6-4


Wt/dry pod (mg)

7d 73-3 71-0 69-3

14 d 68-0 72-7 68-3

Salt effect 70-7 71-9 68-8


Dry wt. plant (g)

7d 13-4 111 31

14 d 11-4 7-5 3-5

Salt effect 12-4 9-3 3-3


Plant height (cm)

7 d 72-7 60-7 33-0

14 d 59-7 52-7 40-7

Salt effect 66-2 56-7 36-9


1-4

5-3

3-3

25-3

81-3

53-3

0-3

2-7

1-5

6 9 0

6 5 0

67-0

1 1

1-7

1-4

25-0

28-3

26-7

1-5

5-6

3-6

32-0

93-3

62-7

0-3

0-7

0-5

47-0

60-3

53-7

1-4

1-8

1-6

2 5 0

26-0

25-5

23-6

1 3 0

327-7

187-2

4-3

5-4

65-9

66-ft

6 0

5-2

43-3

41-6


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490 Ayoub Salt Tolerance in Senna

accum ulated in greater amo unts fromCaCl2treatm ents th an from NaCl. Increasing

su bs tra te conten t of CaCl2 increased shoot Cl, Ca, and Mg contents w ith slight de-

crease in K contents.

Effect of frequency of irrigation ivith salt water on senna yield and yield componen ts

Results of senna pod yield and yield components from different NaCl levels are

shown in Table 3.

' P od yield was significantly affected b y sa lt levels, frequency of irriga tion, an d

the ir interaction. W atering every7d with lower-salt wa ters resulted in apprec iably

higher yields th an w atering every 14 d. Con trary to this, frequent irrigation w ith

high-salt waters injured plants and resulted in lower pod yields than irrigation

every 14 d with the same water.

The number of pods per pot in the various treatments were comparable to pod

yield while increasing salt level resulted in a small but significant P < 0-05)

depression in pod weight.

Plant survival was significantly reduced by salt levels higher than 10-0 mmhos

cm

1

in the soil. This effect was more noticeable at the shorter watering interval

than at the longer watering interval, indicating that the effect of NaCl salinity on

sen na was not solely an osmotic phenom enon. Injure d p lants contained considerable

am ounts of

Cl

which was closely related to the degree of visible injury.

Po d yield was highly correlated w ith pod num ber (r = 0-9947), less with pla nt

survival (r = 0-7221), and least with pod weight (r = 0-3818).

Dry vxight per plant and plantTieight

Significant reductions in dry matter yields and plant heights occurred at soil

salinities of 10-0 mmhos cm

1

and above. W hen soil salinity was raised from 7-5

6-0-

5-0-

v

e

p

o

y

i

e

d

3 3-0-

2

eo

3 2-0-

l-0


8/9

Ayoub

Salt Tolerance in Senna

491

to 10-1 mm hos cm

1

reductions of65and 35 per cent were found in dry m atte r and

pla nt height, respectively. Increasing th e watering interva l from 7 to 14 d reduced

both parameters but not significantly.

The relationship between pod yield and Cl contents of senna leaves is demon-

strated in Fig. 3. Significant yield reduction occurred when the Cl content of the

blade was above 28 m Eq per 100 g dry w t. Fifty per cent yield reduction occurred

a tClcontent of about 62 m Eq , and at Cl content of greater th an 110 m E q pod yield

was very low. The Na contents also varied with NaCl levels, but these variations

seemed to be of minor magnitude.

DISCUSSION

Senna was shown to be fairly tolerant of salinity at the germination stage. A 50

per cent reduction in germination was reached at salt levels between 20-0 and 24-0

mmhos cm

1

. By way of contra st, a 50 per cent reduction in germ ination was found

at 13-0 for groundnuts (Shalhevet, Reiniger, and Shimshi, 1969), 14-0 for tomatoes

(van H oorn, 1970), and 21-0-30-5 mm hos cm

1

for rice (Pearson, Ayers, an d E ber-

hard, 1966). The relatively higher tolerance of senna to salinity during germina-

tion is not surprising since it is a crop originating from regions with a dry climate

and where salinity problems usually exist . The optimum temperature at which

senna could germ inate satisfactorily at high salinity levels was found to be between

28 and 30 C. The significant interac tion of soil salinity an d air tem per atu re re-

ported in this study might be imp ortan t in determining optimum sowing dates on

saline soils. Senna seeds germinated in soils high in exchangeable sodium (ESP of

35),

bu t mo st of the seedlings died shortly after. T he chlorotic sym ptom s appearing

in seedlings growing in high ES P levels couldbedue to the to xic effects of bica rbo na te

ions resulting in high pH values.

Salt type effects were considered important in senna since Na2SC>4 effects were

generally less detrimental to the plant growth than were those of CaCl2 or NaCl

of the same salinity. Plants treated with chloride salts were damaged to a greater

extent indicating the more deleterious effects of chloride ion. With chloride salinity,

CaCl2 was more toxic tha n N aCl. I t w ould appear t h at t he high chloride conc entra-

tion in the plant tissue produces the dr astic decrease in plan t growth. I t is possible

that the high sodium levels in plants found in some treatments could be due to

chloride injury to mem branes giving rise to passive sodium u pta ke .

Senna very rapidly absorbed chloride from the root media and accu m ulated toxic

amounts of it in the leaves. Visible chloride injury symptoms occurred at foliar

chloride concentration of abo ut 4270 m Eq per 100 g dry w t., pla nt g row th w as

retarded at about85m Eq , and pla nt survival was highly imp aired at chloride levels

of more tha n 140 m Eq . In its sensitivity to chloride injury, senna behaves in a like

manner to avocado, citrus, and grapes but contrary to most plant species which are

more sensitive to sulphate salts (Mengel, 1973).

Fo r good pod yields of senna, NaCl salinity should not exceed ab out 8-0 m m hos

cm

1

in the soil, but satisfactory yields may be obtained up to 15-0 mmhos cm

1

,

similar to safnower and wheat (Bernstein, 1970).


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492 Ayoub Salt T olerance in Senna

More frequent irriga tion w ith saline w ater induced, earlier and more severe inju ry

than less frequent irrigation. Bernstein and Francois (1975) found that more fre-

quent sprinkling with saline waters resulted in greater osmotic shock than less

frequen t wa tering. Moreover, it was noted in this stud y th at w ater use by the crop

was reduced greatly under high salinity. It is, therefore, inadvisable to give extra

water to senna under saline conditions.

In conclusion, the following points can be mentioned. Senna is moderately toler-

ant to salinity. It seems to be more salt tolerant at germination and later growth

stages , th e seedling stage being the most sensitive. Avoiding adverse environm ental

conditions like high air temperature (Francois and Goodin, 1972), low relative

humidity (O'Leary, 1975), and bad cultural practices (Sandoval and Benz, 1973)

at that critical stage may improve the salinity tolerance by senna and its survival

in the field.

ACKNOWLEDGEMENTS

The author is grateful to the Director General, A.R.C, Sudan for permission to

publish this paper and to D r. R. H. Nieman ofU.S. Salinity Laboratory, Riverside,

for his valuable comments and encouragement.

L I T E R A T U R E C I T E D

AYOTTB, ALI

T., 1975. J. exp. Bot. 26 ,

891-96.

BE RN S T E I N , L., 1970.Agric. Inform. Bull.N o.283,U.S . Dept. Agrio.

and FRANCOIS, L. E., 1975.

Agron. J.

67, 185-90.

CHANG,C. E., and D BE G N E , H. E., 1955.Proc.SoilSet. Soc. A m. 19, 29-35.

CHAPMAN, H. D., and PRATT, P. F . , 1961.I nMethods

of ana lysis for soils, plants and waters.

Univ.Calif.,R iverside, Div. Agrio. Sei.

FBANCOIS ,

L. E., and

GOODIN,

J. R., 1972.

Agron. J.

64, 272-73.

GUPTA,R ., 1971.

Indian Fmg.

21, 29-32.

M E N G E L , K., 1973. First FAO /SIDA Semina r for plant scientists from A frica and Near E ast,

Cairo, Egypt, 1-20 September, 1973.

O ' L E A R Y , J. W., 1975.

PL

Soil,42 ,717-21.

PEARSON, J. A., AYERS,A. D., and EBEBHABD,D. L., 1966.Soil.

Sri.

38, 777-80.

RI CH A RD S ,L. A. (Ed.), 1954.Diagnosis and improvement of saline

and alkali soils.

U.S. Dept.

Agric. Handbook No. 60.

SANDOVAL,F . M., and BE N Z ,L. C, 1973.

Soil

Sci.,166, 100-5.

SHALHEVET,J ., RE I N I G E R, P., and SHXHSHI,D.1969.

Agron, J.

61 ,384-7.

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Beghdad, Iraq, 5-14 December 1970.



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