Chapter 5 Cassava Botany and Physiology -...

Chapter 5Cassava Botany and Physiology

Alfredo Augusto Cunha AlvesEmbrapa Cassava and Fruits, Caixa Postal 007, 44.380–000, Cruz das Almas,

Bahia, Brazil

Introduction

Cassava is a perennial shrub of the familyEuphorbiaceae, cultivated mainly for its starchyroots. It is one of the most important food staplesin the tropics, where it is the fourth most impor-tant source of energy. On a worldwide basis itis ranked as the sixth most important source ofcalories in the human diet (FAO, 1999). Giventhe crop’s tolerance to poor soil and harsh clima-tic conditions, it is generally cultivated by smallfarmers as a subsistence crop in a diverse rangeof agricultural and food systems. Althoughcassava is a perennial crop, the storage roots canbe harvested from 6 to 24 months after planting(MAP), depending on cultivar and the growingconditions (El-Sharkawy, 1993). In the humidlowland tropics the roots can be harvested after6–7 months. In regions with prolonged periodsof drought or cold, the farmers usually harvestafter 18–24 months (Cock, 1984). Moreover,the roots can be left in the ground withoutharvesting for a long period of time, making ita very useful crop as a security against famine(Cardoso and Souza, 1999).

Cassava can be propagated from either stemcuttings or sexual seed, but the former is thecommonest practice. Propagation from true seedoccurs under natural conditions and is widelyused in breeding programmes. Plants from trueseed take longer to become established, and theyare smaller and less vigorous than plants from

cuttings. The seedlings are genetically segre-gated into different types due to theirreproduction by cross-pollination. If propagatedby cuttings under favourable conditions, sprout-ing and adventitious rooting occur after 1 week.

Morphological and AgronomicCharacteristics

Cassava, which is a shrub reaching 1–4 mheight, is commonly known as tapioca, manioc,mandioca and yuca in different parts of theworld. Belonging to the dicotyledon familyEuphorbiaceae, the Manihot genus is reported tohave about 100 species, among which the onlycommercially cultivated one is Manihot esculentaCrantz. There are two distinct plant types: erect,with or without branching at the top, orspreading types.

The morphological characteristics ofcassava are highly variable, which indicate ahigh degree of interspecific hybridization. Thereare many cassava cultivars in several germplasmbanks held at both international and nationalresearch institutions. The largest germplasmbank is located at Centro Internacional deAgricultura Tropical (CIAT), Colombia, withapproximately 4700 accessions (Bonierbaleet al., 1997), followed by EMBRAPA’s collectionin Cruz das Almas, Bahia, with around 1700accessions (Fukuda et al., 1997), representing

©CAB International 2002. Cassava: Biology, Production and Utilization(eds R.J. Hillocks, J.M. Thresh and A.C. Bellotti) 67

79Z:\Customer\CABI\A4101 - Hillocks - Cassava\A4212 - Hillocks - Cassava #R.vpMonday, February 04, 2002 11:21:53 AM

Color profile: DisabledComposite Default screen

the germplasm of the following Brazilian eco-systems: lowland and highland semiarid tropics,lowland humid subtropics, lowland subhumidtropics, lowland humid tropics, and lowland hotsavannah. The cassava genotypes are usuallycharacterized on the basis of morphological andagronomic descriptors. Recently, the Interna-tional Plant Genetic Resources Institute (IPGRI)descriptors (Gulick et al., 1983) were revised, anda new version was elaborated, in which 75descriptors were defined, 54 being morpho-logical and 21 agronomic (Fukuda et al., 1997).Morphological descriptors (for example, lobeshape, root pulp colour, stem external colour)have a higher heritability than agronomic (suchas root length, number of roots per plant and rootyield). Among morphological descriptors, thefollowing were defined as the minimum or basicdescriptors that should be considered for identify-ing a cultivar: (i) apical leaf colour; (ii) apical leafpubescence; (iii) central lobe shape; (iv) petiolecolour; (v) stem cortex colour; (vi) stem externalcolour; (vii) phyllotaxis length; (viii) root ped-uncule presence; (ix) root external colour; (x)root cortex colour; (xi) root pulp colour; (xii) rootepidermis texture; and (xiii) flowering.

Given the large number of cassava genotypescultivated commercially and the large diversityof ecosystems in which cassava is grown, it isdifficult to make a precise description of the mor-phological descriptors as there is a genotype-by-environmental conditions interaction. Thus,in addition to morphological characterization,molecular characterization, based mainly onDNA molecular markers, has been very useful inorder to evaluate the germplasm genetic diver-sity (Beeching et al., 1993; Fregene et al., 1994).

Roots

Roots are the main storage organ in cassava.In plants propagated from true seeds a typicalprimary tap root system is developed, similarto dicot species. The radicle of the germinatingseed grows vertically downward and developsinto a taproot, from which adventitious rootsoriginate. Later, the taproot and some adventi-tious roots become storage roots.

In plants grown from stem cuttings the rootsare adventitious and they arise from the basal-cut surface of the stake and occasionally from the

buds under the soil. These roots develop to makea fibrous root system. Only a few fibrous roots(between three and ten) start to bulk and becomestorage roots. Most of the other fibrous rootsremain thin and continue to function in waterand nutrient absorption. Once a fibrous rootbecomes a storage root, its ability to absorb waterand nutrients decrease considerably. The storageroots result from secondary growth of the fibrousroots; thus the soil is penetrated by thin roots,and their enlargement begins only after thatpenetration has occurred.

Anatomically, the cassava root is not atuberous root, but a true root, which cannotbe used for vegetative propagation. The maturecassava storage root has three distinct tissues:bark (periderm), peel (or cortex) and paren-chyma. The parenchyma, which is the edibleportion of the fresh root, comprises approxi-mately 85% of total weight, consisting of xylemvessels radially distributed in a matrix of starch-containing cells (Wheatley and Chuzel, 1993).

The peel layer, which is comprised ofsclerenchyma, cortical parenchyma and phloem,constitutes 11–20% of root weight (Barriosand Bressani, 1967). The periderm (3% of totalweight) is a thin layer made of a few cells thickand, as growth progresses, the outermost por-tions usually slough off. Root size and shapedepend on cultivar and environmental condi-tions; variability in size within a cultivar isgreater than that found in other root crops(Wheatley and Chuzel, 1993). Table 5.1 listsmorphological and agronomic characteristics ofthe root and its variability in cassava.

Stems

The mature stem is woody, cylindrical andformed by alternating nodes and internodes. Onthe nodes of the oldest parts of the stem, thereare protuberances, which are the scars left bythe plant’s first leaves. A plant grown from stemcuttings can produce as many primary stems asthere are viable buds on the cutting. In somecultivars with strong apical dominance, onlyone stem develops.

The cassava plant has sympodial branch-ing. The main stem(s) divide di-, tri- or tetra-chotomously, producing secondary branchesthat produce other successive branchings. These

68 A.A.C. Alves



Botany and Physiology 69

Root characteristic Variability Reference

MorphologicalExternal colour

Cortex colourPulp (parenchyma) colourEpidermis texturePedunculeConstrictionShape

AgronomicNo. storage roots/plant

Weight of storage roots/plant

Weight of one storage root

Length of storage root

Diameter of storage root

Diameter of fibrous rootDepth of fibrous rootAmylose in root starchProtein in whole rootProtein in pulp (parenchyma)

Protein in peel

DM in whole fresh root

DM in peel

DM in pulp

Carbohydrates in whole rootCarbohydrates in peelCarbohydrates in pulp

(parenchyma)Starch in whole root

Starch in peel

White or cream; yellow; lightbrown; dark brownWhite or cream; yellow; pink; purpleWhite; cream; yellow; pinkSmooth; rugoseSessile; pedunculate; bothNone or little; medium; manyConical; conical–cylindrical;cylindrical; irregular

3–14

0.5–3.4 kg FW

0.17–2.35 kg

15–100 cm

3–15 cm

0.36–0.67 mmUp to 260 cm13–21% FW1.76–2.68% FW1.51–2.67% FW1.0–6.0% DW2.79–6.61% FW7.0–14.0% DW23–43%

15–34%

23–44%

85–91% DW60–83% DW88–93% DW

20–36% FW

77% DW14–25% FW44–59% DW

Fukuda and Guevara (1998)

Fukuda and Guevara (1998)Fukuda and Guevara (1998)Fukuda and Guevara (1998)Fukuda and Guevara (1998)Fukuda and Guevara (1998)Fukuda and Guevara (1998)

Dimyati (1994); Wheatley andChuzel (1993); Ramanujam andIndira (1983); Pinho et al. (1995)Dimyati (1994); Wheatley andChuzel (1993); Ramanujam andIndira (1983)Barrios and Bressani (1967);Ramanujam and Indira (1983)Wheatley and Chuzel (1993);Barrios and Bressani (1967);Pinho et al. (1995)Wheatley and Chuzel (1993);Barrios and Bressani (1967);Pinho et al. (1995)Connor et al. (1981)Connor et al. (1981)O’Hair (1990)Barrios and Bressani (1967)Barrios and Bressani (1967)Wheatley and Chuzel (1993)Barrios and Bressani (1967)Wheatley and Chuzel (1993)Barrios and Bressani (1967);Ghosh et al. (1988); Ramanujamand Indira (1983); O’Hair (1989)Wheatley and Chuzel (1993);Barrios and Bressani (1967);O’Hair (1989)Wheatley and Chuzel (1993);Barrios and Bressani (1967);O’Hair (1989)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)

Wholey and Booth (1979);O’Hair (1989); Ternes et al.(1978)Ghosh et al. (1988)O’Hair (1989)Wheatley and Chuzel (1993)

Continued

Table 5.1. Some morphological and agronomic characteristics of roots and their variability in cassava.



branchings, which are induced by flowering,have been called ‘reproductive branchings’.

Stem morphological and agronomic char-acteristics are very important to characterizinga cultivar (Table 5.2). The variation of thesecharacteristics depends on cultivar, culturalpractice and climatic conditions.

Leaves

Cassava leaves are simple, formed by the laminaand petiole. The leaf is lobed with palmatedveins. There is generally an uneven number oflobes, ranging from three to nine (occasionally11). Only a few cultivars are characterized byhaving three-lobed mature vegetative leaves,which may represent the primitive ancestralform (Rogers and Fleming, 1973). Leaves nearthe inflorescence are generally reduced in sizeand lobe number (most frequently three-lobed),but the one closest to the base of the inflores-cence is frequently simple and unlobed.

Leaves are alternate and have a phyllotaxyof 2/5, indicating that from any leaf (leaf 1) thereare two revolutions around the stem to reach thesixth (leaf 6) in the same orthostichy as leaf 1. Inthese two revolutions there are five successiveintermediate leaves (not counting leaf 1).

The main leaf morphological and agro-nomic characteristics and their variation aregiven in Table 5.3. Many of them (mainly themorphological ones) are used to characterizecultivars and may vary with environmentalconditions and plant age.

Mature leaves are glabrous and each leafis surrounded by two stipules (approximately

0.5–1.0 cm long), which remain attached to thestem when the leaf is completely developed(CIAT, 1984). The petiole length of a fully openedleaf normally varies from 5 to 30 cm, but mayreach up to 40 cm.

The upper leaf surface is covered with ashiny, waxy epidermis. Most stomata are locatedon the lower (abaxial) surface of the leaves;only a few can be found along the main vein onthe upper (adaxial) surface (Cerqueira, 1989). Of1500 cultivars studied, only 2% had stomataon the adaxial surface (El-Sharkawy and Cock,1987a). The stomata on the upper surface arealso functional and bigger than those on theundersurface. Both are morphologically para-cytic, with two small guard cells surroundedby two subsidiary cells (Cerqueira, 1989). Thenumber of stomata per leaf area range from278 to 700 mm−2, and all stomatal pores canoccupy from 1.4 to 3.1% of the total leaf area(Table 5.3).

Flowers

Cassava is a monoecious species producing bothmale (pistillate) and female (staminate) flowerson the same plant. The inflorescence is generallyformed at the insertion point of the reproductivebranchings; occasionally inflorescences can befound in the leaf axils on the upper part of theplant. The female flowers, located on the lowerpart of the inflorescence, are fewer in numberthan male flowers, which are numerous on theupper part of the inflorescence. On the sameinflorescence, the female flowers open 1–2weeks before the male flowers (protogyny).

70 A.A.C. Alves

Root characteristic Variability Reference

Starch in pulp (parenchyma)

Peel in whole rootCrude fibre in whole rootCrude fibre in peel

Crude fibre in pulp(parenchyma)

Total sugars

26–40% FW70–91% DW11–20% FW3.8–7.3% DW9.2–21.2% DW5.0–15.0% DW2.9–5.2% DW3.0–5.0% DW1.3–5.3% DW

O’Hair (1989)Wheatley and Chuzel (1993)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Wheatley and Chuzel (1993)Barrios and Bressani (1967)Wheatley and Chuzel (1993)Wheatley and Chuzel (1993)

DM, dry matter; FW, fresh weight; DW, dry weight.

Table 5.1. Continued.

82Z:\Customer\CABI\A4101 - Hillocks - Cassava\A4212 - Hillocks - Cassava #S.vpTuesday, February 12, 2002 3:24:53 PM


Male and female flowers on different branchesof the same plant can open at the same time.Normally, cassava is cross-pollinated by insects;thus it is a highly heterozygous plant.

The flowers do not have a calyx or corolla,but an indefinite structure called perianth orperigonium, made up of five yellow, reddish orpurple tepals. The male flower is half the size ofthe female flower. The pedicel of the male floweris thin, straight and very short, while that of thefemale flower is thick, curved and long. Inside themale flower, there is a basal disk divided into tenlobes. Ten stamens originate from between them.They are arranged in two circles and support theanthers. The five external stamens are separatedand longer than the inner ones, which jointogether on the top to form a set of anthers. Thepollen is generally yellow or orange, varyingfrom 122 to 148 µm in size, which is very largecompared to other flowering plants (Ghosh et al.,1988). The female flower also has a ten-lobedbasal disk, which is less lobulated than the maleflower. The ovary is tricarpellary with six ridgesand is mounted on the basal disk. The threelocules contain one ovule each. A very small styleis located on top of the ovary, and a stigma with

three undulated, fleshy lobes originates from thestyle.

Fruit and seeds

The fruit is a trilocular capsule, ovoid or globu-lar, 1–1.5 cm in diameter and with six straight,prominent longitudinal ridges or aristae. Eachlocule contains a single carunculate seed. Thefruit has a bicidal dehiscence, which is a combi-nation of septicidal and loculicidal dehiscences,with openings along the parallel plane of thedissepiments and along the midveins of thecarpels, respectively. With this combination ofdehiscences, the fruits open into six valves caus-ing an explosive dehiscence, ejecting the seedssome distance (Rogers, 1965). Fruit maturationgenerally occurs 75–90 days after pollination(Ghosh et al., 1988). The seed is ovoid–ellipsoidal, approximately 100 mm long, 6 mmwide and 4 mm thick. The weight varies from 95to 136 mg per seed (Ghosh et al., 1988). Thesmooth seed coat is dark brown, mottled withgrey. The seeds usually germinate soon after col-lection, taking about 16 days for germination.


Stem characteristic Variability Reference

MorphologicalCortex (collenchyma) colourExternal colour

Phyllotaxis length

Epidermis colour

Growth habitApical stem colourBranching habit

AgronomicDiameter of mature stem

Plant height

No. of nodes from planting–1st branch level

No. of days from planting–1st branch level

No. of apices/plant

Yellow; light green; dark greenOrange; green–yellow; gold; darkbrown; silver; grey; dark brownShort (< 8 cm); medium (8–15 cm);large (> 15 cm)Cream; light brown; dark brown;orangeStraight; zigzagGreen; green-purple; purpleErect; dichotomous; trichotomous;tetrachotomous

2–8 cm

1.20–3.70 m

22–96

49–134

2.8–27.5

Fukuda and Guevara (1998)Fukuda and Guevara (1998)



Fukuda and Guevara (1998)Fukuda and Guevara (1998)Fukuda and Guevara (1998)

CIAT (1984); Ramanujam andIndira (1983)Ramanujam and Indira (1983);Ramanujam (1985); Veltkamp(1985a); Pinho et al. (1995)Veltkamp (1985a)

Veltkamp (1985a)

Pinho et al. (1995)

Table 5.2. Some morphological and agronomic characteristics of stems and their variability in cassava.



Growth and Development

Plant developmental stages

As cassava is a perennial shrub it can growindefinitely, alternating periods of vegetativegrowth, storage of carbohydrates in the roots,and even periods of almost dormancy, broughton by severe climatic conditions such as lowtemperature and prolonged water deficit. Thereis a positive correlation between the totalbiomass and storage root biomass (Fig. 5.1;Ramanujam, 1990). During its growth, thereare distinct developmental phases. The occur-rence, duration and existence of each phase

depend on several factors related to varietal dif-ferences, environmental conditions and culturalpractices. The initial growth (at 15-day inter-vals) from emergence to 150 days is presented inFig. 5.2. Growth at 60-day intervals during thefirst cycle (0–360 days after planting; DAP) isshown in Fig. 5.3. The results in these two fig-ures are consistent with other authors (Howelerand Cadavid, 1983; Ramanujam and Biradar,1987; Távora et al., 1995; Peressin et al., 1998).The periods and main physiological eventsduring the growth of a cassava plant underfavourable conditions in the field can bevisualized in these figures and are summarizedbelow:

72 A.A.C. Alves

Leaf characteristic Variability Reference

MorphologicalApical leaf colour

Apical pubescenceShape of central lobe

Petiole colour

Mature leaf colour

Protuberance of leaf scarsNo. of lobes

AgronomicPetiole length

Total chlorophyllCentral lobe lengthCentral lobe widthNo. of stomata/leaf area

in adaxial epidermis

Relative area of stomatapore (% from leaf area)

Stipule lengthLeaf thicknessDM in mature leafFibre in mature leafAsh in mature leafProtein in mature leaf

Soluble carbohydrates

Light green; dark green; green–purple;purpleAbsent; presentOvoid; elliptic–lanceolate; obovate–lanceolate; oblanceolate; lanceolate;linear; pandurate; linear–pyramidal;linear–pandurate; linear–hostatilobadaGreen–yellow; green; green–red;red-green; red; purpleLight green; dark green; green-purple;purpleNo protuberance; protuberant3; 5; 7; 9; 11

5–30 cm9–20 cm2.18–2.86 mg g−1 leaf FW4–20 cm1–6 cm278–700 mm−2

1.4–3.1%

0.5–1.0 cm100–120 µm25%4.58% DW8.28% DW7.1–8.9% FW28.8% DW11.36% FW44.84% DW






Ghosh et al. (1988)CIAT (1984)Ramanujam and Jos (1984)CIAT (1984)CIAT (1984)Ghosh et al. (1988); Cerqueira(1989); Splittstoesser and Tunya(1992); Connor and Palta (1981)Cerqueira (1989); Pereira andSplittstoesser (1990)CIAT (1984)Pereira and Splittstoesser (1990)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)

DM, dry matter; FW, fresh weight; DW, dry weight.

Table 5.3. Some morphological and agronomic characteristics of leaves and their variability in cassava.




Fig. 5.1. Relationship between dry weight (DW) of whole plant (x) and DW of storage roots (y) forindividual plants of a field trial at the University of the West Indies: y = 0.56x−34; r 2 = 0.96; n = 112.(Source: Boerboom, 1978.)

Fig. 5.2. Partitioning of dry matter during the initial development of cassava cv. Cigana, Cruz dasAlmas, Bahia, Brazil. (Source: Porto, 1986.)



Emergence of sprouting – 5–15 DAP

• From 5–7 DAP the first adventitious rootsarise from the basal cut surface of the stakeand occasionally from the buds under thesoil.

• 10–12 DAP the first sprouting occurs,followed by small leaves which start toemerge (Conceição, 1979).

• Emergence is achieved at 15 DAP.

Beginning of leaf development and formationof root system – 15–90 DAP

• The true leaves start to expand around 30DAP (Fig. 5.2) when the photosyntheticprocess starts to contribute positively toplant growth.

• Until 30 DAP, shoot and root growthdepends on the reserves of the stem cutting.

• The fibrous roots start to grow, replacingthe first adventitious roots. These new rootsstart to penetrate in the soil, reaching40–50 cm deep, and function in water andnutrient absorption (Conceição, 1979).

• Few fibrous roots (between three and 14)will become storage roots, which can bedistinguished from fibrous roots from 60 to90 DAP (Cock et al., 1979). At 75 DAP the

storage roots represent 10–15% of total drymatter (DM; Fig. 5.2).

Development of stems and leaves (canopyestablishment) – 90–180 DAP

• Maximum growth rates of leaves and stemsare achieved in this period, and the branch-ing habit and plant architecture is defined(Fig. 5.3).

• From 120 to 150 DAP the leaves are able tointercept the most of the incident light oncanopy (Veltkamp, 1985c).

• Maximum canopy size and maximum DMpartition to leaves and stems are accom-plished (Howeler and Cadavid, 1983;Ramanujam, 1985; Távora et al., 1995).

• The storage root continues to bulk.• The most active vegetative growth for

cassava occurs in this period (Ramanujam,1985).

High carbohydrate translocation to roots –180–300 DAP

• Photoassimilate partition from leaves toroots is accelerated, making the bulkingof storage roots faster (Fig. 5.3).

74 A.A.C. Alves

Fig. 5.3. Growth of cassava plant during the first cycle (12 months). Average of two varieties. DAP,days after planting. Graph made from data of Lorenzi (1978).



• The highest rates of DM accumulationin storage roots occur within this period(Fig. 5.3; Boerboom, 1978; Távora et al.,1995; Peressin et al., 1998).

• Leaf senescence increases, hastening rate ofleaf fall (Fig. 5.3).

• Stem becomes lignified (Conceição, 1979).

Dormancy – 300–360 DAP

• Rate of leaf production is decreased.• Almost all leaves fall and shoot vegetative

growth is finished.• Only translocation of starch to root is kept,

and maximum DM partition to the roots isattained.

• This phase occurs mainly in regions withsignificant variation in temperature andrainfall.

• The plant completes its 12-month cycle,which can be followed by a new period ofvegetative growth, DM accumulation in theroots and dormancy again.

Leaf area development

The analyses of crop growth and yield areusually evaluated on the basis of two parame-ters: leaf area index (LAI), i.e. leaf area per unitground area, and net assimilatory rate (NAR),i.e. the rate of DM production per unit leaf area.

In cassava a positive correlation between theleaf area or leaf area duration and yield of stor-age roots has been reported, indicating that leafarea is crucial in determining crop growth rateand the storage bulking rate of cassava (Sinhaand Nair, 1971; Cock, 1976; Cock et al., 1979).

For cassava the leaf area per plant dependson the number of active apices (branchingpattern), the number of leaves formed/apex, leafsize and leaf life. Given that there are significantvarietal variations and influence of environmen-tal conditions (Veltkamp, 1985a), it is importantto characterize the development of cassava leafarea and its components. Table 5.4 lists valuesof some parameters related to leaf growth thathave been found in cassava. These parametersare discussed below.

After leaf emergence (folded, 1 cm long)and under normal conditions, the cassava leafreaches its full size on days 10–12. Leaf life (fromemergence to abscission) depends on cultivar,shade level, water deficit and temperature (Cocket al., 1979; Irikura et al., 1979). It ranges from40 to 210 days (Table 5.4), but is commonly60–120 days (Cock, 1984).

There are marked differences in leaf sizeamong the different cultivars, and the size varieswith the age of the plant. The leaves producedfrom 3 to 4 MAP are those that become the larg-est; maximum total leaf area is reached from 4 to5 MAP (Cock et al., 1979; Irikura et al., 1979).Leaf size is influenced by changing the branching


Leaf growth parameter Value Reference

Individual leaf area

Expansion period (from emergence tofull size)Leaf longevity (from fully expanded toabscission)Leaf life (from emergence to abscission)

No. leaves retained/plantLeaf production rate/shootLeaf shedding rate/plantTotal leaf areaCumulative no. of leaves/apex

50–600 cm2

12 days

36–100 days

40–210 days

44–1464–22 week−1

10–24 leaves week−1

1.24–3.38 m2

117–162

Ramanujam (1982); Splittstoesserand Tunya (1992); Veltkamp (1985a)Conceição (1979)

Ramanujam and Indira (1983);Conceição (1979)Splittstoesser and Tunya (1992);Irikura et al. (1979); Ramanujam(1985); Veltkamp (1985a)Ramanujam and Indira (1983)Ramanujam and Indira (1983)Ramanujam and Indira (1983)Ramanujam and Indira (1983)Veltkamp (1985a); Cock et al. (1979)

Table 5.4. Parameters related to leaf growth during the first cycle (12 months) and some values foundin cassava.



pattern. Larger leaves are produced when thenumber of active apices is reduced (Tan andCock, 1979). The rate of leaf formation decreaseswith plant age and is lower at low temperatures(Irikura et al., 1979).

Differences in mean LAI are closely relatedto the rate of root bulking. The optimal LAI forstorage root bulking rate is 3–3.5 (Cock et al.,1979) and exists over a wide range of tempera-ture (Irikura et al., 1979). Initial leaf area devel-opment is slow, taking 60–80 DAP before an LAIof 1.0 is reached. From 120 to 150 DAP the lightinterception by the canopy is around 90% withan LAI of 3 (Veltkamp, 1985a). In order to obtainhigh storage root yields, the crop should reach anLAI of 3–3.5 as quickly as possible and maintainthat LAI for as long as possible (Cock et al., 1979;Veltkamp, 1985a). Substantial leaf abscissionbegan at LAI values of 5.0–6.0 (Keating et al.,1982a).

Temporal development of cell divisionand cell expansion

Leaf area development is largely dependent oncell division and cell expansion processes, whichdetermine the number of cells per mature leafand cell size, respectively. Thus the final leaf areais directly affected by the rate and duration ofcell division and expansion (Takami et al., 1981;Lecoeur et al., 1995). A temporal developmentof cell division and expansion for adaxial epider-mal cells in cassava has been proposed by Alves(1998; Fig. 5.4), in which the transition fromleaf cell division to cell expansion processes isdiscrete and occurs when leaf area reached 5%of its final size, corresponding to the first foldedleaf toward the top. Thus when the leaf starts tounfold, almost all cell division stops and rapidcell expansion starts.

Dry matter partitioning and source–sinkrelationship

During cassava growth the carbohydrates fromphotosynthesis have to be distributed to assuregood development of the source (active leaves)and provide DM to the sink (storage roots, stemand growing leaves). Cassava DM is translocatedmainly to stems and storage roots, and DM

accumulation in the leaves decreases during thecrop cycle. Until 60–75 DAP, cassava accumu-lates DM more in leaves than in stems andstorage roots, not including the stem cutting(Fig. 5.2). Then the storage roots increaserapidly, reaching 50–60% of the total DMaround 120 DAP (Fig. 5.2; Howeler andCadavid, 1983; Távora et al., 1995). After thefourth month, more DM is accumulated inthe storage roots than the rest of the plant. Atharvest (12 months) DM is present mainly inroots, followed by stems and leaves (Fig. 5.3;Howeler and Cadavid, 1983). Thus, during thegrowth cycle, the DM distribution to the differ-ent parts is constant with a high positive linearcorrelation of the total DM with shoot and rootDM (Fig. 5.1; Veltkamp, 1985d).

The period of maximum rates of DMaccumulation depends on genotypes and grow-ing conditions. Lorenzi (1978) at high latitudeand Oelsligle (1975) at high altitude reportedmaximum rates of DM accumulation at 4–6and 7 months, respectively. Under more tropicalconditions, where growth is faster, Howeler andCadavid (1983) found an earlier period of maxi-mum rates, at 3–5 MAP. The distribution of DMto the economically useful plant parts is mea-sured by harvest index (HI). In cassava HI repre-sents the efficiency of storage root productionand is usually determined by the ratio of storageroot weight to the total plant weight. Significantdifferences in HI have been reported among

76 A.A.C. Alves

Fig. 5.4. Temporal development of cell divisionand cell expansion processes during cassava leafdevelopment in adaxial epidermal cells. (Source:Alves, 1998.)



cultivars, indicating that it can be used as a selec-tion criterion for higher yield potential in cas-sava. HI values of 0.49–0.77 have been reportedafter 10–12 MAP (Lorenzi, 1978; Cavalcanti,1985; Pinho et al., 1995; Távora et al., 1995;Peressin et al., 1998). Although DM distributionis constant, its accumulation depends uponphotoassimilate availability (source activity) andsink capacity of the storage parts. The number ofstorage roots and their mean weight are yieldcomponents that determine sink capacity. Thesignificant positive correlation of photosyntheticrate with root yield and total biomass, as wellas the correlations between LAI, interceptionof radiation and biomass production (Williams,1972; Mahon et al., 1976; El-Sharkawy andCock, 1990; Ramanujam, 1990), indicates thatdemand for photoassimilates by roots increasesthe photosynthetic activity.

The balance between ‘source’ and ‘sink’activity is essential for the plant to reach itsmaximum productivity. Studies have shownthat up to 25% reduction in the number ofstorage roots did not affect total or root DM andthe IAF (Cock et al., 1979). On the other hand,Ramanujam and Biradar (1987) observed thatreduction of 50–75% in storage roots did affectroot growth rate without changing shoot growthrate, indicating that shoot growth is independentof storage root growth. Influence of source size onDM production shows that the NAR and storageroot growth rate is reduced when the source sizeis increased from LAI 3.0 to 6.0 (Ghosh et al.,1988).

Flowering

Little is known about flowering in cassava, andsome clones have never been known to flower.Flowering can start 6 weeks after plantingalthough the precise flowering time dependson cultivar and environment. It appears thatcassava flowers best at moderate temperatures(approximately 24°C). It has been suggestedthat forking is related to the onset of flowering,which is promoted by long days in somecultivars. Usually, the apical meristem becomesreproductive when branching occurs, but theabortion of flowers is very common.

Keating et al. (1982a) evaluated cassavaat 12 different planting dates at a high latitude

(27° 37′ S), where photoperiods range from 14.8to 11.2 h. Concentration of first flowering andforking occurred in photoperiods > 13.5 h. Thisresult is consistent with Bruijn (1977) andCunha and Conceição (1975), who suggestedflowering in cassava may be promoted byincreasing day length.

Photosynthesis

Cassava photosynthesis follows a C3 pathway(Veltkamp, 1985e; Edwards et al., 1990; Angelovet al., 1993; Ueno and Agarie, 1997) withmaximum photosynthetic rates varying from13 to 24 µmol CO2 m−2 s−1 under greenhouseor growth chamber conditions (Mahon et al.,1977b; Edwards et al., 1990) and from 20 to35 µmol CO2 m−2 s−1 in the field (El-Sharkawyand Cock, 1990). It exhibits a high CO2 compen-sation point, from 49 to 68 µl l−1, typical of C3

plants (Mahon et al., 1977a; Edwards et al.,1990; Angelov et al., 1993). In field-growncassava, photosynthesis has high optimumtemperature (35°C) and wide plateau (25–35°C;El-Sharkawy and Cock, 1990) and is not lightsaturated up to 1800 µmol PAR m−2 s−1

(El-Sharkawy et al., 1992b) or 2000 µmol PARm−2 s−1 (Angelov et al., 1993). Thus cassavais adapted to a tropical environment, requiringhigh temperature and high solar radiation foroptimal leaf development and for expression ofits photosynthetic potential. Both storage rootyield and total biomass show positive correlationwith photosynthesis rate (El-Sharkawy andCock, 1990; Ramanujam, 1990).

Morphologically, cassava leaves combinesome novel characteristics related to highproductivity and drought tolerance and, conse-quently, to photosynthesis. The lower mesophyllsurface is populated with papillose-type epi-dermal cells, while the upper surface is fairlysmooth, with scattered stomata and trichomes.The papillae appear to add about 15% to leafthickness and to lengthen the diffusion pathfrom the stomatal opening to the bulk air perhapstwo- to threefold (Angelov et al., 1993). Cassavaleaves have distinct green bundle-sheath cells,with small, thin-walled cells, spatially separ-ated below the palisade cells (different fromKranz-type leaf anatomy). In addition to




performing C3 photosynthesis, these cells mayfunction in transport of photosynthates in theleaf. In Kranz anatomy, typical of C4 plants, thebundle sheaths are surrounded by and all indirect contact with many mesophyll cells(Edwards et al., 1990).

Cyanide Content

All cassava organs, except seeds, contain cyano-genic glucoside (CG). Cultivars with < 100 mgkg−1 fresh weight (FW) are called ‘sweet’ whilecultivars with 100–500 mg kg−1 are ‘bitter’cassava (Wheatley et al., 1993). The most abun-dant CG is linamarin (85%), with lesser amountsof lotaustralin. Total CG concentration dependson cultivar, environmental condition, culturalpractices and plant age (McMahon et al., 1995).The variation found in some parts of cassava isshown in Table 5.5.

Linamarin, which is synthesized in the leafand transported to the roots, is broken down bythe enzyme linamarase, also found in cassavatissues (Wheatley and Chuzel, 1993). Whenlinamarin is hydrolysed, it releases HCN, a vola-tile poison (LD50–60 mg for humans; Cooke andCoursey, 1981); but some cyanide can be detoxi-fied by the human body (Oke, 1983). In intactroots the compartmentalization of linamarasein the cell wall and linamarin in cell vacuolesprevents the formation of free cyanide. Uponprocessing, the disruption of tissues ensures thatthe enzyme comes into contact with its substrate,resulting in rapid production of free cyanide viaan unstable cyanhydrin intermediary (Wheatleyand Chuzel, 1993). Juice extraction, heating,

fermentation, drying or a combination of theseprocessing treatments aid in reducing the HCNconcentration to safe levels (O’Hair, 1990).

Physical Deterioration ofStorage Roots

Cassava roots have the shortest postharvestlife of any of the major root crops (Ghosh et al.,1988). Roots are highly perishable and usuallybecome inedible within 24–72 h after harvestdue to a rapid physiological deterioration pro-cess, in which synthesis of simple phenolic com-pounds that polymerize occurs, forming blue,brown and black pigments (condensed tannins;Wheatley and Chuzel, 1993). It is suggested thatpolyphenolic compounds in the roots oxidize toquinone-type substances, which is complexedwith small molecules like amino acids to formcoloured pigments that are deposited in thevascular bundles (Ghosh et al., 1988). Theaccumulation of the coumarin, scopoletin, isespecially rapid, reaching 80 mg kg−1 dryweight (DW) in 24 h (Wheatley and Chuzel,1993). Tissue dehydration, especially at sites ofmechanical damage to the roots encourages therapid onset of deterioration. The phenolic com-pounds may be released on injury. The changesduring storage of roots depend upon conditionand duration of storage, physiological state ofthe stored material and varietal characteristics(Ghosh et al., 1988).

Polyphenol oxidase (PPO) is an enzymethat oxidizes phenols to quinone. Any processthat inhibits PPO, such as heat treatment, coldstorage, anaerobic atmosphere and dipping

78 A.A.C. Alves

Part of plant Total cyanide concentration Source

Root pulp (parenchyma)

Root peel

Leaf

3–121 mg 100 g−1 DW3–135 mg 100 g−1 DW1–40 mg 100 g−1 FW6–55 mg 100 g−1 DW5–77 mg 100 g−1 DW17–267 mg 100 g−1 FW1–94 mg 100 g−1 DW0.3–29 mg 100 g−1 FW

Barrios and Bressani (1967)Wheatley and Chuzel (1993)Barrios and Bressani (1967)Wheatley and Chuzel (1993)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)Barrios and Bressani (1967)

DW, dry weight; FW, fresh weight.

Table 5.5. Cyanide concentration in different parts of the cassava plant.



roots in solutions of inhibitors (e.g. ascorbicacid, glutathione and KCN) prevents vascularstreaking (Ghosh et al., 1988).

Secondary deterioration can follow physio-logical or primary deterioration 5–7 days afterharvest. This is due to microbial infection ofmechanically damaged tissues and results inthe same tissue discoloration with vascularstreaks spreading from the infected tissues(Wheatley and Chuzel, 1993).

Environmental Effects onCassava Physiology

Cassava is found over a wide range of edaphicand climatic conditions between 30°N and 30°Slatitude, growing in regions from sea level to2300 m altitude, mostly in areas consideredmarginal for other crops: low-fertility soils,annual rainfall from < 600 mm in the semiaridtropics to > 1500 mm in the subhumid andhumid tropics. Given the wide ecologicaldiversity, cassava is subjected to highly varyingtemperatures, photoperiods, solar radiation andrainfall.

Temperature

Temperature affects sprouting, leaf size,leaf formation, storage root formation and, con-sequently, general plant growth. The behaviour

of cassava under the temperature variationsthat usually occur where cassava is normallycultivated indicates that its growth is favourableunder annual mean temperatures ranging from25 to 29°C (Conceição, 1979), but it cantolerate from 16 to 38°C (Cock, 1984). Table5.6 summarizes the ranges of temperature andtheir principal physiological effects on cassavadevelopment.

At low temperatures (16°C) sprouting ofthe stem cutting is delayed, and rate of leafproduction, total and storage root DW aredecreased (Cock and Rosas, 1975). Sproutingis hastened when the temperature increasesup to 30°C but is inhibited with temperatures> 37°C (Keating and Evenson, 1979). Astemperature decreases, leaf area developmentbecomes slower because the maximum size ofindividual leaves is smaller, and fewer leavesare produced at each apex although leaf life isincreased (Irikura et al., 1979). At a temperatureof 15–24°C, the leaves remain on the plant for upto 200 days (Irikura et al., 1979), while at highertemperatures leaf life is 120 days (Splittstoesserand Tunya, 1992).

There is a genotype-by-temperature inter-action for yield ability. Irikura et al. (1979) evalu-ated four cultivars under different temperaturesand found that higher yields were obtained atdifferent temperatures according to the cultivar,indicating that the effect of natural selectionis highly significant on varietal adaptation(Table 5.7).


Air temperature (°C) Physiological effects

< 17 or > 3728.5–30< 1516–3825–29< 1720–242825–3030–4016–30

Sprouting impairedSprouting faster (optimum)Plant growth inhibitedCassava plant can growOptimum for plant growthReduction of leaf production rate, total and root DWLeaf size and leaf production rate increased; leaf life shortenedFaster shedding of leaves; reduction in no. branchesHighest rates of photosynthesis in greenhouseHighest rates of photosynthesis in the fieldTranspiration rate increases linearly and then declines

Sources: Wholey and Cock (1974); Cock and Rosas (1975); Mahon et al. (1977b); Conceição (1979);Irikura et al. (1979); Keating and Evenson (1979); El-Sharkawy et al. (1992b).DW, dry weight.

Table 5.6. Effect of temperature on cassava development.



The main effect of temperature is on bio-logical production, as DM partitioning does notchange much when cassava is cultivated underdifferent temperatures (Cock and Rosas, 1975).Higher temperatures are associated with agreater crop growth rate (CGR) and high photo-synthetic rate. El-Sharkawy et al. (1992b)evaluated the potential photosynthesis of threecultivars from contrasting habits under differentgrowing environments and verified that photo-synthetic rate increased with increasing temper-ature, reaching its maximum at 30–40°C. In allcultivars photosynthesis was substantially lowerin leaves that had developed in the cool climatethan in those from the warm climate. The highsensitivity of photosynthesis to temperaturepoints to the need for genotypes more tolerantto low temperature, which could be used in thehighland tropics and subtropics.

Photoperiod

Day length affects several physiological pro-cesses in plants. The differences in day lengthin the tropical region are very small, varyingfrom 10 to 12 h throughout the year. Thusphotoperiod may not limit cassava root pro-duction in this region. On the other hand, therestrictions regarding cassava distribution out-side the tropical zone can be due to effects of daylength variation on its physiology. Althoughstudies about day length effect in cassava arescarce, tuberization, photoassimilates partition-ing and flowering are reportedly affected.

Experiments in which the day length wasartificially changed have shown that the optimallight period for cassava is around 12 h, withprobable varietal differences in the critical day

length (Bolhuis, 1966). Long days promotegrowth of shoots and decrease storage rootdevelopment, while short days increase storageroot growth and reduce the shoots, withoutinfluencing total DW (Fig. 5.5). The increasein shoot DW under long days is a result ofsignificant increases in plant height, leaf areaper plant, number of apices per plant, andnumber of living leaves per apex (Veltkamp,1985b). This suggests an antagonistic relation-ship between shoot growth and development ofthe storage roots in response to variation in daylength.

There are varietal differences in sensitivityto long days (Carvalho and Ezeta, 1983). Underfield conditions, Veltkamp (1985b) submittedthree genotypes to two day lengths (12 and 16 h)during the whole growth period. He observedthat the percentage decrease in storage root yieldunder the long day was greatest in M Col 1684(47%) and least in M Col 22 (13%; Table 5.8).Yield differences resulted mainly from decreasedefficiency of storage root production or HI under16-h days because total DM was greater under16-h days. No day-length effect was found for thecrop weight at which the starch accumulation inthe roots apparently started (AISS values; Table5.8). Thus the storage root yield reduction seemsto be more related to a change in the distributionpatterns of DM rather than to a delay in storageroot initiation. Considering that photoperiod pri-marily affects shoots and a secondary responseoccurs in the roots (Keating et al., 1982b) andthat shoot growth has preference over rootgrowth (Cock et al., 1979; Tan and Cock, 1979),long photoperiods may increase the growthrequirements of the shoots, thereby reducing theexcess carbohydrates available for root growth(Veltkamp, 1985b).

80 A.A.C. Alves

Temperature (°C)

Variety 20 24 28

M Col 22M Mex 59M Col 113Popayán

9.322.824.228.9

27.738.826.115.7

39.430.423.99.4

Source: Irikura et al. (1979).

Table 5.7. Fresh root yield (t ha−1) of four contrasting cassava types at 12months after planting (MAP) under three different temperature regimes.



Solar radiation

The commonest cassava production system isintercropping with other staple crops. In LatinAmerica and Africa, cassava is usually associ-ated with an earlier maturing grain crop such asmaize, rice or grain legumes (beans, cowpeas or

groundnuts; Mutsaers et al., 1993). Cassavais also intercropped with perennial vegetation(Ramanujam et al., 1984). Cassava is usuallyplanted after the intercropped species. Evenwhen it is planted at the same time, the associ-ated crop such as maize is established faster thancassava. Thus in an associated cropping system


Fig. 5.5. Effect of day length on cassava dry matter distribution 16 weeks after planting. Vertical linesindicate twice the standard error of total dry weight (DW), stem DW and storage root DW.

Genotype Day lengthTotal DM(t ha−1)a

DW storage root(t ha−1)

Harvest Index(HI)

AISSb

(t ha−1)

M Col 1684

M Ptr 26

M Col 22

Naturalc

16 hd

Natural16 hNatural16 h

16.717.314.515.915.519.5

9.14.68.14.99.58.3

0.540.270.610.420.560.31

0.550.250.600.360.650.45

Source: Veltkamp (1985b).aIncludes weight of fallen leaves.bAISS, apparent initial start of starch accumulation; corresponds to crop weight at which starchaccumulation apparently starts in roots.cNatural = approximately 12 h.d16 h = 12 h of natural day length + 4 h of artificial light.DW, dry weight.

Table 5.8. Cassava dry matter (DM) production and distribution 272 days after planting (DAP) under16 h and natural day length (approximately 12 h).



cassava is always subjected to different degreesof shading and low light intensity in the earlystages of development. Considering that cassavais a crop that requires high solar radiationto perform photosynthesis more efficiently (El-Sharkawy et al., 1992b), it is very important toknow the effect of shade on cassava develop-ment and production. Ramanujam et al. (1984)evaluated 12 cassava cultivars under the shadein a coconut garden (85–90% shading). Undershading, the root bulking process started about3 weeks after that in plants grown withoutshading, and the number of storage roots perplant and NAR was reduced under shading.Okoli and Wilson (1986) submitted cassava tosix shade regimes and observed that all levels ofshade delayed storage root bulking and at 20,40, 50, 60 and 70% shade reduced cassava yieldby 43, 56, 59, 69 and 80%, respectively.

In relation to shoots, under field conditions,shading increases plant height and the leavestend to become adapted to low light conditions byincreasing leaf area per unit weight (Fukai et al.,1984; Okoli and Wilson, 1986; Ramanujamet al., 1984) and shortening leaf life only undersevere shading. Under ideal growing conditions,cassava leaves have a life of up to 125 days(Splittstoesser and Tunya, 1992). Levels of shadeup to about 75% have very little effect on leaf life,

but under 95–100% shade, leaves abscise within10 days (Cock et al., 1979).

Aresta and Fukai (1984) observed that only22% shade decreased both fibrous root elonga-tion rate (53%) and storage root growth rate(36%) without altering shoot growth rate, whichwas significantly decreased (32%) only under68% shade. Thus under limited photosynthesiscaused by low solar radiation, most of the photo-synthates are utilized for shoot growth, affectingstorage root development significantly, showingthat the shoots are a stronger sink than roots.

Water deficit

Cassava is commonly grown in areas receiving< 800 mm rainfall year−1 with a dry season of4–6 months, where tolerance to water deficit isan important attribute. Although it is a drought-tolerant crop, growth and yield are decreased byprolonged dry periods. The reduction in storageroot yield depends on the duration of the waterdeficit and is determined by the sensitivity ofa particular growth stage to water stress. Thecritical period for water-deficit effect in cassavais from 1 to 5 MAP – the stages of root initiationand tuberization. Water deficit during at least 2months of this period can reduce storage root

82 A.A.C. Alves

Fig. 5.6. Effect of water deficit during different growth periods on cassava yield.



yield from 32 to 60% (Connor et al., 1981; Portoet al., 1988). Figure 5.6 shows the root yieldreduction caused by water deficit imposed for 2months during successive 2-month periods from1 to 11 MAP. Clearly, they found that theseverer effect corresponded to stress occurringfrom 1 to 5 MAP (i.e. period of rapid leaf growthand tuberization) compared with the laterperiod of storage root bulking.

Drought tolerance

Plants respond to water deficit at many differ-ent levels: morphological, physiological, cellularand metabolic. The responses are dependentupon the duration and severity of stress, thegenotype of the stressed plant, the stage ofdevelopment, and the organ and cell type inquestion (Bray, 1994). Multiple responses allowthe plant to tolerate water stress. Some of theseresponses and the current status of knowledgewith regard to cassava are discussed here.

Control of stomatal closure andleaf growth

A primary response to water stress is stomatalclosure, which decreases photosynthetic CO2

assimilation and, in turn, growth. Stomata havea high capacity to respond to changes in thewater status of the plant and atmosphere. Theyclose as the leaf water potential decreases andwhen the vapour pressure deficit between theleaf and the air increases (generally due to adecrease in relative humidity). As stomata arethe route by which CO2 enters the leaf, stress-induced decreases in stomatal aperture canlimit the rate of CO2 diffusion into the leaf and,therefore, the rate of photosynthesis.

When water is available, cassava maintainsa high stomatal conductance and can keepinternal CO2 concentration high; but whenwater becomes limiting, the plant closes stomatain response to even small decreases in soil waterpotential (El-Sharkawy and Cock, 1984). Therapid closure of the stomata and the resultingdecline in transpiration lessens the decreasein leaf water potential and soil water depletion,thereby protecting leaf tissues from desiccation(Ike, 1982; Palta, 1984; El-Sharkawy and Cock,

1984; Cock et al., 1985). This response to earlystages of soil water depletion has been describedas isohydric, a behaviour shared by cowpeas,maize and several other crops (Tardieu andSimonneau, 1998). Leaf area growth is alsodecreased in response to water stress but israpidly reversed following the release fromstress (Connor et al., 1981; Palta, 1984;El-Sharkawy and Cock, 1987b; Baker et al.,1989). This response limits the development ofplant transpirational surface area during waterdeficit and keeps sink demand well balanced withplant assimilatory capacity.

Leaf conductance to water vapour has beenevaluated as an indicator of the capacity ofdifferent cassava genotypes to prevent waterloss under prolonged drought. Considerablevariation has been observed in leaf conductance(Porto et al., 1988), and this parameter seemsto be useful for pre-selecting sources of germ-plasm conferring adaptation to prolonged dryperiods.

Abscisic acid accumulation

Many authors have reported that a substantialnumber of drought responses in plants canbe mimicked by external application of abscisicacid (ABA) to well-watered plants (Davies et al.,1986; Trewavas and Jones, 1991). This treat-ment promotes characteristic developmentalchanges that can help the plant cope with waterdeficit, including decrease of stomatal con-ductance (MacRobbie, 1991; Trejo et al., 1993),restriction of shoot growth (Creelman et al.,1990) and leaf area expansion (Van Volken-burgh and Davies, 1983; Lecoeur et al., 1995)and stimulation of root extension (Sharp et al.,1993, 1994; Griffiths et al., 1997). All theseeffects of ABA application, together with theobservation that environmental stress stimu-lates ABA biosynthesis and ABA release fromsites of synthesis to action sites, suggest a rolefor ABA as a stress hormone in plants. More-over, studies have indicated that for certainplant responses, sensitivity to water deficit iscorrelated with changes in ABA concentrations(Trejo et al., 1995; Borel et al., 1997) and geno-typic responsiveness to ABA (Blum and Sinmena,1995; Cellier et al., 1998). Information about




ABA accumulation in cassava has not beenreported in the literature.

Alves and Setter (2000) published thefirst report concerning ABA in cassava. Theycultivated five cassava genotypes in pots in agreenhouse and evaluated the temporal patternsof ABA accumulation in mature leaves and inimmature expanding leaves, during water deficitand after release from stress to determine theextent to which the stress and recovery responseof leaf area growth is associated with the tempo-ral pattern of ABA accumulation. At 3 and 6days after withholding irrigation, all genotypesaccumulated large amounts of ABA in bothexpanding and mature leaves, but these highABA levels were almost completely reversed inrespect of control levels after 1 day of rewatering(Fig. 5.7). Correspondingly, young leaves haltedleaf expansion growth and transpiration ratedecreased. Young leaves accumulated moreABA than mature leaves both in control andstressed treatments (Fig. 5.7). This rapid returnto control ABA levels corresponded with a rapidrecovery of leaf area growth rates. This rapidreduction in leaf area growth and stomatalclosure may be due to cassava’s ability tosynthesize rapidly and accumulate ABA at anearly phase of a water-deficit episode.

Osmotic adjustment

One means of increasing drought tolerance isby accumulation of osmotically active solutes,so that turgor and turgor-dependent processesmay be maintained during episodes of drydown.Osmotic adjustment (OA), defined as the differ-ence in osmotic potential between control andstressed plants, allows cell enlargement andplant growth at high water stress and allowsstomata to remain partially open and CO2 assim-ilation to continue at low water potentials thatare otherwise inhibitory (Pugnaire et al., 1994).

In cassava OA has not been thoroughlyexamined. Although leaf water potentialremains relatively unchanged during waterdeficit episodes (Connor and Palta, 1981; Cocket al., 1985; El-Sharkawy et al., 1992a), a resultsuggestive of little or no OA, such observationsdo not rule it out. Furthermore, these studiesinvolved mature leaves, not young organs,which might especially benefit from accumula-tion of osmolytes. Alves (1998) evaluated therole of OA in cassava by measuring the osmoticcomponent of leaf water potential in mature,expanding and folded leaves. The largestincrease in solutes caused by water deficitoccurred in the youngest tissue (folded leaves)

84 A.A.C. Alves

Fig. 5.7. Abscisic acid (ABA) concentration in expanding and mature cassava leaves in control after 3and 6 days of water deficit, followed by 1 and 3 days of rewatering; average of five genotypes with threereplicates; bars represent SEM (n = 15); data from Alves and Setter (2000).



and the extent of OA increased progressivelyfrom mature to folded leaves. As young tissues(meristems) are involved in regrowth andrecovery after drought, further research isneeded to give a fuller picture of cassava’sresponses to water deficit.

References

Alves, A.A.C. (1998) Physiological and developmentalchanges in cassava (Manihot esculenta Crantz)under water deficit. PhD thesis, Cornell Univer-sity, Ithaca, New York, 160 pp.

Alves, A.A.C. and Setter, T.L. (2000) Response ofcassava to water deficit: leaf area growth andabscisic acid. Crop Science 40, 131–137.

Angelov, M.N., Sun, J., Byrd, G.T., Brown, R.H. andBlack, C.C. (1993) Novel characteristics ofcassava, Manihot esculenta Crantz, a reputedC3–C4 intermediate photosynthesis species.Photosynthesis Research 38, 61–72.

Aresta, R.B. and Fukai, S. (1984) Effects of solar radia-tion on growth of cassava (Manihot esculentaCrantz). II. Fibrous root length. Field CropsResearch 9, 361–371.

Baker, G.R., Fukai, S. and Wilson, G.L. (1989) Theresponse of cassava to water deficits at variousstages of growth in the subtropics. AustralianJournal of Agricultural Research 40, 517–528.

Barrios, E.A. and Bressani, R. (1967) Composiciónquímica de la raíz y de la hoja de algunasvariedades de yuca Manihot. Turrialba 17,314–320.

Beeching, J.R., Marmey, P., Gavalda, M.C., Noirot, M.,Haysom, H.R., Hughes, M.A. and Charrier, A.(1993) An assessment of genetic diversity withina collection of cassava (Manihot esculenta Crantz)germplasm using molecular markers. Annals ofBotany 72, 515–520.

Blum, A. and Sinmena, B. (1995) Isolation and charac-terization of variant wheat cultivars for ABAsensitivity. Plant, Cell and Environment 18, 77–83.

Boerboom, B.W.J. (1978) A model of dry matter distri-bution in cassava (Manihot esculenta Crantz).Netherlands Journal of Agricultural Science 26,267–277.

Bolhuis, G.G. (1966) Influence of length of the illumi-nation period on root formation in cassava(Manihot utilissima Pohl). Netherlands Journal ofAgricultural Science 14, 251–254.

Bonierbale, M., Guevara, C., Dixon, A.G.O., Ng, N.Q.,Asiedu, R. and Ng, S.Y.C. (1997) Cassava. In:Fuccillo, D., Sears, L. and Stapleton, P. (eds)Biodiversity in Trust. Cambridge University Press,Cambridge, pp. 1–20.

Borel, C., Simonneau, T., This, D. and Tardieu, F.(1997) Stomatal conductance and ABA con-centration in the xylem sap of barley lines ofcontrasting genetic origins. Australian Journalof Plant Physiology 24, 607–615.

Bray, E.A. (1994) Alterations in gene expression inresponse to water deficit. In: Basra, A.S. (ed.)Stress-Induced Gene Expression in Plants. Hard-wood Academic Publishers, Chur, Switzerland,pp. 1–23.

Bruijn, G.H. (1977) Influence of daylength on theflowering of cassava. Tropical Root Tuber CropsNewsletter 10, 1–3.

Cardoso, C.E.L. and Souza, J. da S. (1999) AspectosAgro-Econômicos da Cultura da Mandioca:Potencialidades e Limitações. DocumentosCNPMF no. 86, EMBRAPA/CNPMF, Cruz dasAlmas, BA, Brazil, 66pp.

Carvalho, P.C.L. de and Ezeta, F.N. (1983) Efeito dofotoperíodo sobre a ‘tuberização’ da mandioca.Revista Brasileira de Mandioca 2, 51–54.

Cavalcanti, J. (1985) Desenvolvimento das raízestuberosas em mandioca (Manihot esculentaCrantz). MSc thesis, Universidade Federal doCeará, Fortaleza, Brazil, 66 pp.

Cellier, F., Conéjéro, G., Breitler, J.C. and Casse, F.(1998) Molecular and physiological responses towater deficit in drought-tolerant and drought-sensitive lines of sunflower. Accumulation ofdehydrin transcripts correlates with tolerance.Plant Physiology 116, 319–328.

Cerqueira, Y.M. (1989) Efeito da deficiência de águana anatomia foliar de cultivares de mandioca(Manihot esculenta Crantz). MSc thesis, Univers-idade Federal da Bahia, Cruz das Almas, Brazil.

CIAT (1984) Morphology of the Cassava Plant; StudyGuide. Centro Internacional de AgriculturaTropical, Cali, Colombia.

Cock, J.H. (1976) Characteristics of high yieldingcassava varieties. Experimental Agriculture 12,135–143.

Cock, J.H. (1984) Cassava. In: Goldsworthy, P.R.and Fisher, N.M. (eds) The Physiology of TropicalField Crops. John Wiley & Sons, Chichester,pp. 529–549.

Cock, J.H. and Rosas, S. (1975) Ecophysiology ofcassava. In: (eds) Symposium on Ecophysiologyof Tropical Crops. Communications Division ofCEPLAC, Ilhéus, Bahia, Brazil, pp. 1–14.

Cock, J.H., Franklin, D., Sandoval, G. and Juri, P. (1979)The ideal cassava plant for maximum yield. CropScience 19, 271–279.

Cock, J.H., Porto, M.C.M. and El-Sharkawy, M.A.(1985) Water use efficiency of cassava. III.Influence of air humidity and water stress on gasexchange of field grown cassava. Crop Science 25,265–272.




Conceição, A.J. da (1979) A Mandioca. UFBA/EMBRAPA/BNB/BRASCAN NORDESTE, Cruzdas Almas, BA.

Connor, D.J. and Palta, J. (1981) Response of cassavato water shortage. III. Stomatal control of plantwater status. Field Crops Research 4, 297–311.

Connor, D.J., Cock, J.H. and Parra, G.E. (1981)Response of cassava to water shortage. I. Growthand yield. Field Crops Research 4, 181–200.

Cooke, R.D. and Coursey, D.G. (1981) Cassava: a majorcyanide-containing food crop. In: Vennesland, B.,Conn, E.E. and Knowles, C.J. (eds) Cyanide inBiology. Academic Press, New York.

Creelman, R.A., Mason, H.S., Bensen, R.J., Boyer, J.S.and Mullet, J.E. (1990) Water deficit and abscisicacid cause differential inhibition of shoot versusroot growth in soybean seedlings. Analysis ofgrowth, sugar accumulation, and gene expres-sion. Plant Physiology 92, 205–214.

Cunha, H.M.P. and Conceição, A.J. da (1975) Induçãoao florescimento da mandioca (Manihot esculentaCrantz) – Nota prévia. In: Projeto Mandioca. Uni-versidade Federal da Bahia, Escola de Agronomia,Cruz das Almas, Convênio UFBA/BRASCANNORDESTE, Brazil, pp. 11–14.

Davies, W.J., Metcalfe, J., Lodge, T.A. and Da Costa,A.R. (1986) Plant growth substances and theregulation of growth under drought. AustralianJournal of Plant Physiology 13, 105–125.

Dimyati, A. (1994) Cassava genetic resources inIndonesia: status and future outlook. In: IPGR,International Network for Cassava GeneticResources. Report of the first meeting of theInternational Network for Cassava GeneticResources, CIAT, Cali, Colombia, 18–23 August1992. International Crop Network Series No. 10.International Plant Genetic Resources Institute,Rome, pp. 66–70.

Edwards, G.E., Sheta, E., Moore, B.D., Dai, Z.,Franceschi, V.R., Cheng, S.-H., Lin, C.-H. and Ku,M.S.B. (1990) Photosynthetic characteristics ofcassava (Manihot esculenta Crantz), a C3 specieswith chlorenchymatous bundle sheath cells.Plant and Cell Physiology 31, 1199–1206.

El-Sharkawy, M.A. (1993) Drought-tolerant cassavafor Africa, Asia and Latin America. BioScience 43,441–451.

El-Sharkawy, M.A. and Cock, J.H. (1984) Water useefficiency of cassava. I. Effects of air humidity andwater stress on stomatal conductance and gasexchange. Crop Science 24, 497–502.

El-Sharkawy, M.A. and Cock, J.H. (1987a) C3-C4 inter-mediate photosynthetic characteristics of cas-sava (Manihot esculenta Crantz). I. Gas exchange.Photosynthesis Research 12, 219–236.

El-Sharkawy, M.A. and Cock, J.H. (1987b) Responseof cassava to water stress. Plant and Soil 100,345–360.

El-Sharkawy, M.A. and Cock, J.H. (1990) Photosynthe-sis of cassava (Manihot esculenta). ExperimentalAgriculture 26, 325–340.

El-Sharkawy, M.A., Hernandez, A.D.P. and Hershey, C.(1992a) Yield stability of cassava during pro-longed mid-season water stress. ExperimentalAgriculture 28, 165–174.

El-Sharkawy, M.A., Tafur, S.M.D. and Cadavid, L.F.(1992b) Potential photosynthesis of cassava asaffected by growth conditions. Crop Science 32,1336–1342.

FAO (1999) www.apps.fao.org/lim500/nph-wrap.pl?FS.CropsAndProducts&Domain=FS&servlet=1. Consulted on October 3, 1999.

Fregene, M.A., Vargas, J., Ikea, J., Angel, F., Tohme, J.,Asiedu, R.A., Akoroda, M.O. and Roca, W.M.(1994) Variability of chloroplast DNA andnuclear ribosomal DNA in cassava (Manihotesculenta Crantz) and its wild relatives. Theoreticaland Applied Genetics 89, 719–727.

Fukai, S., Alcoy, A.B., Llamelo, A.B. and Patterson, R.D.(1984) Effects of solar radiation on growth ofcassava (Manihot esculenta Crantz). I. Canopydevelopment and dry matter growth. Field CropsResearch 9, 347–360.

Fukuda, W.M.G. and Guevara, C.L. (1998). DescritoresMorfológicos e Agronômicos para a Caracterização deMandioca (Manihot esculenta Crantz). DocumentosCNPMF no.78. EMBRAPA/CNPMF, Cruz dasAlmas BA, Brazil.

Fukuda, W.M.G., Silva, S.O. and Porto, M.C.M. (1997)Caracterização e Avaliação de Germoplasma deMandioca (Manihot esculenta Crantz). Catalog.EMBRAPA/CNPMF, Cruz das Almas BA, Brazil.

Ghosh, S.P., Ramanujam, T., Jos, J.S., Moorthy, S.N.and Nair, R.G. (1988) Tuber Crops. Oxford & IBHPublishing Co., New Delhi, pp. 3–146.

Griffiths, A., Jones, H.G. and Tomos, A.D. (1997)Applied abscisic acid, root growth and turgorpressure response of roots of wild-type andthe ABA-deficient mutant, Notabilis, of tomato.Journal of Plant Physiology 151, 60–62.

Gulick, P., Hershey, C. and Esquinas Alcazar, J. (1983)Genetic Resources of Cassava and Wild Relatives.Rome.

Howeler, R.H. and Cadavid, L.F. (1983) Accumulationand distribution of dry matter and nutrients dur-ing a 12-month growth cycle of cassava. FieldCrops Research 7, 123–139.

Ike, I.F. (1982) Effect of water deficits on transpiration,photosynthesis and leaf conductance in cassava.Physiologia Plantarum 55, 411–414.

86 A.A.C. Alves



Irikura, Y., Cock, J.H. and Kawano, K. (1979) The phys-iological basis of genotype-temperature interac-tions in cassava. Field Crops Research 2, 227–239.

Keating, B.A. and Evenson, J.P. (1979) Effect of soiltemperature on sprouting and sprout elongationof stem cuttings of cassava. Field Crops Research 2,241–252.

Keating, B.A., Evenson, J.P. and Fukai, S. (1982a) Envi-ronmental effects on growth and development ofcassava (Manihot esculenta Crantz). I. Crop devel-opment. Field Crops Research 5, 271–281.

Keating, B.A., Evenson, J.P. and Fukai, S. (1982b) Envi-ronmental effects on growth and development ofcassava (Manihot esculenta Crantz). III. Assimilatedistribution and storage organ yield. Field CropsResearch 5, 293–303.

Lecoeur, J., Wery, J., Turc, O. and Tardieu, F. (1995)Expansion of pea leaves subjected to short waterdeficit: cell number and cell size are sensitive tostress at different periods of leaf development.Journal of Experimental Botany 46, 1093–1101.

Lorenzi, J.O. (1978) Absorção de macronutrientes eacumulação de matéria seca para duas cultivaresde mandioca. MSc thesis, Universidade de SãoPaulo, Escola Superior de Agricultura Luis deQueiroz, Piracicaba, Brazil, 92 pp.

MacRobbie, E.A.C. (1991) Effect of ABA on ion trans-port and stomatal regulation. In: Davies, W.J. andJones, H.G. (eds) Abscisic Acid: Physiology andBiochemistry. BIOS, Oxford, pp. 153–168.

Mahon, J.D., Lowe, S.B. and Hunt, L.A. (1976)Photosynthesis and assimilate distribution inrelation to yield of cassava grown in controlledenvironments. Canadian Journal of Botany 54,1322–1331.

Mahon, J.D., Lowe, S.B. and Hunt, L.A. (1977a) Varia-tion in the rate of photosynthesis CO2 uptake incassava cultivars and related species of Manihot.Photosynthetica 11, 131–138.

Mahon, J.D., Lowe, S.B., Hunt, L.A. and Thiagarajah,M. (1977b) Environmental effects on photosyn-thesis and transpiration in attached leaves of cas-sava (Manihot esculenta Crantz). Photosynthetica11, 121–130.

McMahon, J.M., White, W.L.B. and Sayre, R.T. (1995)Cyanogenesis in cassava (Manihot esculentaCrantz). Journal of Experimental Botany 46,731–741.

Mutsaers, H.J.W., Ezumah, H.C. and Osiru, D.S.O.(1993) Cassava-based intercropping: a review.Field Crops Research 34, 431–457.

Oelsligle, D.D. (1975) Accumulation of dry matter,nitrogen, phosphorus, and potassium in cassava(Manihot esculenta Crantz). Turrialba 25, 85–87.

O’Hair, S.K. (1989) Cassava root starch content anddistribution varies with tissue age. HortScience 24,505–506.

O’Hair, S.K. (1990) Tropical root and tuber crops.Horticultural Reviews 12, 157–166.

Oke, O.L. (1983) The mode of cyanide detoxification.In: Nestel, B. and MacIntyre, R. (eds) ChronicCassava Toxicity. International DevelopmentResearch Centre, Ottawa, pp. 97–104.

Okoli, P.S.O. and Wilson, G.F. (1986) Response ofcassava (Manihot esculenta Crantz) to shadeunder field conditions. Field Crops Research 14,349–360.

Palta, J.A. (1984) Influence of water deficits ongas-exchange and the leaf area development ofcassava cultivars. Journal of Experimental Botany35, 1441–1449.

Pereira, J.F. and Splittstoesser, W.E. (1990) Anatomy ofthe cassava leaf. Proceedings International Societyof Tropical Horticulture 34, 73–78.

Peressin, V.A., Monteiro, D.A., Lorenzi, J.O., Durigan,J.C., Pitelli, R.A. and Perecin, D. (1998) Acúmulode matéria seca na presença e na ausência deplantas infestantes no cultivar de mandioca SRT59 – Branca de Santa Catarina. Bragantia 57,135–148.

Pinho, J.L.N. de, Távora, F.J.A.F., Melo, F.I.O. andQueiroz, G.M. de (1995) Yield components andpartitioning characteristics of cassava in thecoastal area of Ceará. Revista Brasileira deFisiologia Vegetal 7, 89–96.

Porto, M.C.M. (1986) Fisiologia da mandioca. Mono-graph presented at VI Curso Intensivo Nacionalde Mandioca, 14–24 October 1986, EMBRAPA/CNPMF, Cruz das Almas BA, Brazil, 21 pp.

Porto, M.C.M., Bessa, J.M.G. and Lira Filho, H.P. (1988)Diferenças varietais no uso da água em mandioca,sob condições de campo no Estado de Pernam-buco. Revista Brasileira de Mandioca 7, 73–79.

Pugnaire, F.I., Endolz, L.S. and Pardos, J. (1994)Constraints by water stress on plant growth. In:Pessarakli, M. (ed.) Handbook of Plant and CropStress. Marcel Dekker, New York, pp. 247–259.

Ramanujam, T. (1982) Leaf area in relation to petiolelength in cassava. Turrialba 32, 212–213.

Ramanujam, T. (1985) Leaf density profile andefficiency in partitioning dry matter amonghigh and low yielding cultivars of cassava(Manihot esculenta Crantz). Field Crops Research10, 291–303.

Ramanujam, T. (1990) Effect of moisture stress onphotosynthesis and productivity of cassava.Photosynthetica 24, 217–224.

Ramanujam, T. and Biradar, R.S. (1987) Growthanalysis in cassava (Manihot esculenta Crantz).Indian Journal of Plant Physiology 30, 144–153.

Ramanujam, T. and Indira, P. (1983) Canopystructure on growth and development ofcassava (Manihot esculenta Crantz). Turrialba 33,321–326.




Ramanujam, T. and Jos, J.S. (1984) Influence oflight intensity on chlorophyll distribution andanatomical characters of cassava leaves.Turrialba 34, 467–471.

Ramanujam, T., Nair, G.M. and Indira, P. (1984)Growth and development of cassava (Manihotesculenta Crantz) genotypes under shade in acoconut garden. Turrialba 34, 267–274.

Rogers, D.J. (1965) Some botanical and ethnologicalconsiderations of Manihot esculenta. EconomicBotany 19, 369–377.

Rogers, D.J. and Fleming, H.S. (1973) A monographof M. esculenta with an explanation of the taxi-metrics methods. Economic Botany 27, 1–113.

Sharp, R.E., Voetberg, G.S., Saab, I.N. and Bernstein, N.(1993) Role of abscisic acid in the regulation ofcell expansion in roots at low water potentials. In:Close, T.J. and Bray, E.A. (eds) Plant Response toCellular Dehydration During Environmental Stress.American Society of Plant Physiologists,Rockville, Maryland, pp. 57–66.

Sharp, R.E., Wu, Y., Voetberg, G.S., Saab, I.N. andLeNoble, M.E. (1994) Confirmation that abscisicacid accumulation is required for maize primaryroot elongation at low water potentials. Journal ofExperimental Botany 45, 1743–1751.

Sinha, S.K. and Nair, T.V. (1971) Leaf area duringgrowth and yielding capacity of cassava. TheIndian Journal of Genetics and Plant Breeding 31,16–20.

Splittstoesser, W.E. and Tunya, G.O. (1992) Cropphysiology of cassava. Horticultural Reviews 13,105–129.

Takami, S., Turner, N.C. and Rawson, H.M. (1981) Leafexpansion of four sunflower (Helianthus annuusL.) cultivars in relation to water deficits. I.Patterns during plant development. Plant, Cell andEnvironment 4, 399–407.

Tan, S.L. and Cock, J.H. (1979) Branching habit as ayield determinant in cassava. Field Crops Research2, 281–289.

Tardieu, F. and Simonneau, T. (1998) Variabilityamong species of stomatal control under fluctuat-ing soil water status and evaporative demand:modeling isohydric and anisohydric behaviours.Journal of Experimental Botany 49, 419–432.

Távora, F.J.A.F., Melo, F.I.O., Pinho, J.L.N. de andQueiroz, G.M. de (1995) Yield, crop growth rateand assimilatory characteristics of cassava atthe coastal area of Ceará. Revista Brasileira deFisiologia Vegetal 7, 81–88.

Ternes, M., Mondardo, E. and Vizzotto, V.J. (1978)Variação do teor de amido na cultura da mandiocaem Santa Catarina. Indicação de Pesquisa no. 23,Empresa Catarinense de Pesquisa Agropecuária,Florianópolis, SC, Brazil.

Trejo, C.L., Davies, W.J. and Ruiz, L.D.M.P. (1993)Sensitivity of stomata to abscisic acid. Aneffect of the mesophyll. Plant Physiology 102,497–502.

Trejo, C.L., Clephan, A.L. and Davies, W.J. (1995)How do stomata read abscisic acid signals? PlantPhysiology 109, 803–811.

Trewavas, A.J. and Jones, H.G. (1991) An assessmentof the role of ABA in plant development. In:Davies, W.J. and Jones, H.G. (eds) AbscisicAcid: Physiology and Biochemistry. BIOS, Oxford,pp. 169–188.

Ueno, O. and Agarie, S. (1997) The intercellulardistribution of glycine decarboxylase in leaves ofcassava in relation to the photosynthetic modeand leaf anatomy. Japanese Journal of Crop Science66, 268–278.

Van Volkenburgh, E. and Davies, W.J. (1983)Inhibition of light-stimulated leaf expansion byabscisic acid. Journal of Experimental Botany 34,835–845.

Veltkamp, H.J. (1985a) Canopy characteristics ofdifferent cassava cultivars. Agricultural UniversityWageningen Papers 85, 47–61.

Veltkamp, H.J. (1985b) Growth, total dry matter yieldand its partitioning in cassava at differentdaylengths. Agricultural University WageningenPapers 85, 73–86.

Veltkamp, H.J. (1985c) Interrelationships betweenLAI, light interception and total dry matter yieldof cassava. Agricultural University WageningenPapers 85, 36–46.

Veltkamp, H.J. (1985d) Partitioning of dry matterin cassava. Agricultural University WageningenPapers 85, 62–72.

Veltkamp, H.J. (1985e) Photosynthesis, transpiration,water use efficiency and leaf and mesophyll resis-tance of cassava as influenced by light intensity.Agricultural University Wageningen Papers 85,27–35.

Wheatley, C.C. and Chuzel, G. (1993) Cassava:the nature of the tuber and use as a raw material.In: Macrae, R., Robinson, R.K. and Sadler, M.J.(eds) Encyclopaedia of Food Science, Food Technol-ogy, and Nutrition. Academic Press, San Diego,California, pp. 734–743.

Wheatley, C.C., Orrego, J.I., Sanchez, T. and Granados,E. (1993) Quality evaluation of cassava corecollection at CIAT. In: Roca, W.M. and Thro, A.M.(eds) Proceedings of the First International ScientificMeeting of the Cassava Biotechnology Network.CIAT, Cartagena, Colombia, pp. 255–264.

Wholey, D.W. and Booth, R.H. (1979) Influence ofvariety and planting density on starch accumula-tion in cassava roots. Journal of the Science of Foodand Agriculture 30, 165–170.

88 A.A.C. Alves



Wholey, D.W. and Cock, J.H. (1974) Onset and rate ofroot bulking in cassava. Experimental Agriculture10, 193–198.

Williams, C.N. (1972) Growth and productivity of tapi-oca (Manihot utilissima). III. Crop ratio, spacingand yield. Experimental Agriculture 8, 15–23.




Chapter 5 Cassava Botany and Physiology -...

Documents

Transcript of Chapter 5 Cassava Botany and Physiology -...