Abstract:
Common bean (Phaseolusvulgaris L.) is sensitive
to water stress. Objective of the study was to select
genotypes resistant to drought and determine traits
associated with drought resistance. One hundred and
eight bean genotypes from University of Nairobi
Bean Research Program, the International Center for
Tropical Agriculture (CIAT), The Gene Bank of Kenya
(GBK) and local varieties were screened in a drought
nursery from 2008 to 2010 at Kabete Field Station. The
experimental design was a split plot with three replicates.
The two irrigation treatments, irrigated (non stress, NS)
and rainfed (drought stressed, DS) were main plots, and
genotypes the sub-plots. The whole experiment received
sprinkler irrigation up to flowering stage to ensure good
establishment and stand uniformity. Irrigated plots (NS)
received supplemental irrigation as required while the
rainfed (DS) plots did not receive further irrigation until
the crop was harvested. Data was collected on days
to flowering, maturity, shoot biomass traits and grain
yield. Yield data under stress and no stress conditions
was used to calculate drought intensity index (DII). A
combined analysis of variance showed that season,
irrigation and genotypic effects were highly significant
(P>0.01). Severe drought (DII=0.72) reduced grain yield
by 63%, while moderate drought (DII=0.3) in 2010
reduced grain yield by 40%. Thirteen genotypes from
three grain types were drought resistant. Grain yield
under drought stress was positively correlated with days
to flowering (r=55**), days to maturity (r=0.64**), pod
harvest index(r=0.57**), and negatively correlated with
pod wall biomass proportion (r=-0.63**). Selection of
common bean genotypes for drought stress may consider
use of seed biomass, pod harvest index and reduced pod
wall biomass proportion by breeders.