Study of the agronomic and physiological response of field bean (phaseolus vulgaris l.) cultivars to soil water deficits

Abstract

Four common bean (Phaseolus vulgaris) cultivars namely, White Haricot, Ulonzo, GLP- 2, Okuodo were grown in the field and glass house experiments and subjected to different watering levels. A fifth variety, GLP-I004 (Mwezi Moja) was used in only one field experiment. In the glass house relatively rapid water stress was imposed by withholding water from plants which had earlier been well watered. Line source sprinkler irrigation was used to impose differential irrigation under field conditions. Leaf water potential, leaf solute potential, leaf relative water content and soil water content were determined in glass house experiments. In the field experiment soil water content, plant biomass, yield and yield components were determined. Results showed that White Haricot and Ulonzo maintained lower total leaf water potentials and leaf solute potentials than GLP-2, Okuodo and GLP-lO04. Further analysis indicated that the two varieties effected osmoregulation which allowed them to maintain fairly constant relative water content over a wider range of decreasing solute potential compared to the other varieties. Field experiments showed that, water stress affected White Haricot and Ulonzo to a significantly lesser extent in terms of biomass and grain yield compared to the other two varieties. It is suggested that adaptation to water stress in common beans is associated with the ability to osmoregulate, a characteristic that is genetically controlled but significantly enhanced by drought environment. White Haricot and Ulonzo which exhibited superior osmoregulation depleted soil moisture to significantly lower values before onset of wilting.