Abstract:
Production of cowpea [Vigna unguiculata (L.) Walp.] is often limited by the low rainfall.
Identification of cowpea genotypes adapted to drought may be a feasible strategy to overcome
the poor plant growth and production in the southern highland region (SHR). Two experiments
were conducted; the first one was conducted during 2007, 2008 and 2009 under midseason
drought (MSD) and late-season droughts (LSD) environments. In both seasons, the drought
stress (DS) and non stress (NS) plots were grown adjacent to each other both in a similar design
and plot size. Overall average of DII for the trials conducted in 2008, 2009 and 2010 were 0.352,
0.394 and 0.458 for MSD and 0.605, 0.615 and 0.661 for LSD indicating that under MSD
experiments were subjected to medium drought stress while LSD experiments were subjected to
sever drought stress. Phenotypical, physiological traits and quantitative indices of stress
tolerance were identified at both environments. Eight IITA genotypes, promising genotypes and
the farmer cultivar, based on high yielding under both NS and DS conditions were evaluated
during 2010, 2011 and 2012 under relatively dry cropping seasons at eight locations; Dabab,
Demnah, Hifan, Shikheen, Torpah, Qaidah, Aodain and the station representing low rainfall
drought stress conditions. The most effective selection criterion, for identifying drought resistant
for phenotypic yield were seed/plants, and for morphological and for physiological traits growth
recovery resistance, relative water content, water use efficiency and proline content and for
quantitative indices of stress tolerance we consider the susceptible tolerant index (STI) was the
most useful trait can be used as selection criterion under both NS and DS as these traits were
positively and significantly correlated trait with the yield under both non stressed (Yp) and stressed (Ys) environments. The results also showed that the IITA genotypes IT93K-503-1,
IT97K-1069-6, IT98K-128-4, IT96K-610, IT98K-529, IT98K-499-39, IT00K-901-5 and IT98K-
205-8 were the most tolerant genotypes and had superior performance under both non stressed
(NS) and drought stressed (DS) environments in comparison with the local and other genotypes.
By using stability analysis only IT93K-503-1, IT98K-128-4, IT96K-610, IT98K-499-39 and
IT98K-205-8 were high average yields, with b-value of 1.00 and a very low (s2
d) approaching
zero, low ecovalence value (W) and highly significant coefficient of determination (r2
).
Coefficient of determination ranged between 53.1% for IT98K-529 and 83.6% for IT98K-128-3
suggesting that linear regression accounted for 53-84% variation in cowpea yield. Thus, these
genotypes performed best across the environments indicating wide adaptability. These genotypes
could be introduced to farmers in these agro-ecological zones. |
