Differences in gas exchange parameters and rooting characteristics of bean cultivars adopted to high and low rainfall zones of Kenya

Abstract

Experiments were conducted in the field and in the glass house to study leaf gas exchange parameters and vertical root growth in common bean cultivars collected from high and low rainfall zones of Kenya and to examine the relationship between them and drought adaptation. The bean cultivars were subjected to two watering levels (high and low). Stomatal conductance and photosynthesis were measured using an infra-red gas analyser system. Downward root growth was monitored using differential placement of herbicides. Cultivars collected from low rainfall zones maintained higher stomatal conductance than those from high rainfall zones under both high and low watering levels. They also exhibited higher rates of downward root penetration. Photosynthetic rates of cultivar from low and high rainfall zones were generally significantly different although the former maintained numerically higher values. It is concluded that drought resistance in beans may be associated with faster downward root penetration which together with osmotic adjustment leads to high stomatal conductance and concomitant high transpiration and photosynthetic rates