The morphological and agronomic characteristics (i.e. roots, stems, leaves, flowers, fruits and seeds) of cassava are discussed, including growth and development (i.e. plant developmental stages, leaf area development, temporal development of cell division and cell expansion, dry matter partitioning and source sink relations, flowering, photosynthesis, cyanide content and physical deterioration of storage roots) environmental effects on cassava physiology (i.e. temperature, photoperiod, solar radiation, drought tolerance, control of stomatal closure and leaf growth, abscisic acid accumulation and osmotic adjustment).

Although cell growth processes were sensitive to mild water deficit, they recovered to a large extent, and much of the reduction in leaf area was caused by developmental delay and a reduction in cell division in the youngest, meristematic leaves.

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Walp], maize (Zea mays L.), and several other crop plants (Tardieu and Simonneau, 1998). In addition, leaf Cassava (Manihot esculenta Crantz) responds to decreases in water area growth is decreased in response to water stress status by pronounced stomatal closure and decreased leaf area growth. and is rapidly reversed following the release from stress Many water deficit responses are thought to be regulated by abscisic acid (ABA). To evaluate the extent to which ABA accumulated in (Connor et al., 1981;Palta, 1984; El-Sharkawy and Cock, a temporal pattern related to water deficit and leaf area growth, five 1987). This response limits the development of plant cassava genotypes were grown in greenhouse conditions and subjected transpirational surface area during water deficit and to water deficit and recovery treatments during the vegetative-growth keeps sink demand well balanced with plant assimilastage. Young and mature leaves were sampled for analysis of area tory capacity. growth and ABA. Under water deficit, leaves from all genotypes A regulatory system that could potentially contribute rapidly accumulated large amounts of ABA in both mature and young to cassava's sensitivity to water deficit is the one involvleaves. Correspondingly, young leaves halted leaf expansion growth ing the stress hormone ABA. In addition to closing and transpiration rate decreased. Young leaves accumulated more stomates, ABA promotes characteristic developmental ABA than mature leaves in both the control and stressed treatments. changes that can help plants cope with water deficit, The high ABA levels under water deficit were completely reversed to control levels after 1 d of rewatering. This rapid return to control including restriction of shoot growth (Creelman et al., ABA levels corresponded with a rapid recovery of leaf area growth 1990) and leaf area expansion (Van Volkenburgh and rates. We postulate that the rapid reduction in leaf area growth and