A Study of the Physiological and Ecological Adaptatton of Comhon Beans ( Phaseolus Vulgaris L) to Drought Stress

Abstract

Two experiments were conducted in the field and one in the ~leenhollse to s t udy d i. f ferences in drought response in ten varieties of common heans, collected from different ecological zones. The bean varieties were treat.ed to two watering levels between Jate vegetative and mid-podding stages. LeRf water and snlut.e potentials were determined using thermocouple psych rome t.er , while stomatal conductances, transpiration rate and n=t. phot.osynt.het; i.crates were determined using the infra-red-gas nnaly~er system. Relative water content, total plant biomass and downw ar-d root penetration were also determined. Varietal differences were observed in J.eafwater and solute potentials, relative water content, stomatal conductance, transpirat.ion rates, net photosynthetic rates and rates of downward roo t growth. Ulonzo and "'hite Haricot (both landraces from low rainfall areas) and variety GLP-I004 (developed for low rainfall areas), maintained lower leaf water and solute pot.onti aI s , However, they had higher stomatal conductances, t.ransp i. rat. i on rates, ne t photosynthet i c rates, re Lative water content and rates of downward root penetration than varieties from high rainfall areas. The study indicated that adaptation to drought stress in common heans is associated with ability to adjust osmotically and rapid downward root growth. The parameters may therefore be used as indicators of drought resistance in beans. Relationship between agroecology and drought resistance was also sugge