Introduction; Literature review; Taxonomy of the grain legumes; Biological structure and growth habit; Photosynthesis and sink demand; Phloem loading; Interorgan transport; Phloem Unloading; Water stress and Photosynthesis; Rate and duration of seed filling; Water stress effects on the translocation of assimilates; Growth and physiology of stressed tissues; Turgor maintenance; Materials and methods; Field studies; Glasshouse studies; Influence of water stress on yield and yield components of cowpea and beans grown under field and glasshouse conditions; Plant and fruit water status; Photosynthesis and water stress; Water stress and translocation; Partitioning of dry matter; Leaf area index (LAI) and net assimilation rate (NAR); Pod and seed growth rate and duration; Anatomical study of vascular system of the funiculus and seed coat of beans plants.

Produtivity of legume crops grown in semi-arid regions of the world is limited by drought. This study was conducted to determine the effect of drought on the physiological and morphorlogical factors associated with productivity of cowpea (Vigna unguiculata (L.) Walp) and bean (Phaseolus vulgaris L.) grown under reduced water levels. Physiological factors measured were photosynthesis, water and osmotic potential, translocation, relative growth rates and dry matter partitioning. Morphological traits of pode and seeds were stutied with scanning electron microscops. Field and glasshouse experiments were conducted under light, temperature, and irrigation regimes. Water stress caused reduction of seed yield in cowpea and bean plants by decressing total biomass and photosynthesis. Bean water potential and turgor of source leaf, pod walls, and seed were similar for both stressed and nonstressed plants over the reproducive period. In both bean and cowpea, partitioning of the total above ground dry matter was similar for both stressed and nonstressed plants. Photosynthetic rates of single leaves from either cowpea or bean were greater for nonstressed than stressed plants.