Dry matter partitioning of bean (Phaseolus vulgaris L.) and cowpea (Vigna unguiculata (L.) Walp.) under water deficit conditions.

Abstract

Productivity 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 morphological 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, RGR and dry matter partitioning. Morphological traits of pods and seeds were studied with scanning electron microscope. Water stress reduced seed yield in cowpea and bean plants by decreasing total biomass and photosynthesis. The source leaf, pod and seed water potential of stressed cowpea was lower than water potential of nonstressed plants. Bean water potential and turgor of source leaf, pod walls, and seed were similar for both stressed and nonstressed plants over the reproductive period. No differences in water potential and turgor were observed between pod walls and seed and source leaves of either cowpea or bean plants. In both bean and cowpea, partitioning of the total above ground dry matter was similar for both stressed and nonstressed plants. However, more dry matter accumulated in seeds than in other plant structures. Photosynthetic rates of single leaves from either cowpea or bean were greater for nonstressed than stressed plants. The duration of seed growth of cowpea and bean was not different between stressed and nonstressed plants; however, rate of seed growth at the end of seed filling period was greater in nonstressed plants. Seed RGR of both stressed and nonstressed cowpea and bean plants declined at about the same time photosynthesis of the source leaf declined. LAI and NAR were greatest in nonstressed cowpea and bean plants. Sixty-one percent of ¹⁴C sucrose taken up by the leaves was translocated to the seeds whereas only about 80% ended up in the pod walls. Pod funiculus of stressed bean plants had more scalariform xylem vessels than nonstressed plants.