ADAPTABILITY AND STABILITY OF COWPEA (Vigna unguiculata) LINES IN KENYA COASTAL REGION
Cowpea (Vigna unguiculata L. Walp.) is one of the most important grain legume grown in sub- Saharan Africa. About 12.5 million tons of cowpea grain are produced worldwide each year with the majority (over 94%) of the production taking place on low input, subsistence farms. This crop is most important in the semi-arid and warm areas of Africa where other crops may fail due to poor adaptation to heat, drought and low soil fertility conditions. The experiment was conducted at Kenya Agricultural Research Institute (KARI), Mtwapa and its sub-centres at Msabaha and Mariakani. The agroecological zones (AEZ‟s) for the sites are; coastal Lowland 3 (CL3) for Mtwapa, coastal lowland 4 (CL4) for Msabaha and coastal lowland 5 (CL5) for Mariakani. The sites have sandy soils with pH of between 5.3 to 6.9. Fifteen cowpea lines were sourced from the KARI Genebank which included three improved cultivars that have been tested in central and eastern regions of Kenya. These genotypes have varying agronomic traits and were collected from various regions of Kenya. They are; K033057, K033073, K003731, K005169, K026753, K027092, K003962, K046781, K028613, K047079, K047078, K047121, KVU 27-1, M 66 and K 80. The checks were the local variety and improve variety K 80. Planting was done in the short rains season of 2012 and in the long rains season of 2013. Planting was done at a spacing of 60 cm × 30 cm. The trial was randomized complete block design (RCBD) with three replications. The location of the sites was at Mtwapa (CL3), Msabaha (CL4) and Mariakani (CL5). The objective of this study was to contribute to increased food production in coastal Kenya through development of high yielding, drought tolerant and farmer acceptable cowpea lines. The data collected included both qualitative and quantitative traits – it was on stand count, days to emergence, days to flowering, days to pod-setting, days to maturity, number of pods per plant and number of seeds in a pod. At maturity the different lines were harvested, weighed with the pods, then threshed and the grain yield per plot measured. 100 seed weight was also recorded per plot. The net plot, or where the data was collected, was from the two middle rows of the plot. The year effects was clearly manifested in the agronomic traits and seed quality of the cowpea evaluated. Generally, the means of 2013 were higher than those of 2012 for days to flowering, podding, maturity, pods per plant, length of pods, height of plants, seeds per pod, seed length, seed width, pod weight, grain yield and seed weight. The potential of the genotypes were better expressed in long rains 2013 compared to short rains 2012 due to conducive weather prevailing in 2013. The superiority of K005169 in all the agroecological zones in grain yield is observed making the genotype a candidate for consideration in the breeding with others to introgress the genes for high yield potential. The 16 genotypes attained maturity within 70 to 76 days after planting and can therefore be classified as early maturing types. Of the 16 genotypes tested in the three agroecological zones of the lowland coast region, five have shown outstanding performance across the test environments. They are K005169, KVU 27-1, M66, K003962 and K046781. These genotypes have manifested their adaptability and stability across test environments and can be recommended for introduction in the region and will contribute to increased production of cowpea.