Response of selected sorghum (sorghum bicolor (l.) Moench) genotypes to striga hermonthica (del.) Benth in western Kenya

Abstract

ABSTRACT Sorghum (Sorghum bicolor (L.) Moench) is an important staple food crop in western Kenya, but its yields are low due to many constraints including; pest and diseases, drought, soil acidity, and parasitic weed Striga hermonthica. In recent years, Striga has been a major cause of yield reduction in western Kenya owing to declining soil fertility and susceptibility of existing cultivars. Several control options such as chemical, biological and cultural methods have been utilized but only with little success realized. This has created renewed interest in resistance breeding for its proper management. The objectives of this study were to: determine the numbers of induced and maximum distance of germinated Striga seeds under laboratory conditions and assess the response in yield components and yield in the selected sorghum genotypes under field Striga hermonthica infestation. A total of 21 sorghum genotypes, 7 obtained from each institution; International Crop Research Institute for the Semi-Arid Tropics, Rongo and Maseno Universities were evaluated in Agar Gel (AG) experiment in Maseno botanical laboratory and in an on-farm trial at Kadel and Nyahera under natural Striga infestation. The AG experiment and field trials were respectively set up in three replications in a completely randomized design and randomized complete block design. Variance analysis (ANOVA) and mean field Striga counts, numbers of induced germinated Striga seeds, Striga damage ratings, maximum distance of the germinated Striga seeds, and yield components and yield were analyzed using a Statistical Analysis System (SAS) software package (release 6.1) tested for significance at 5% level and means separated using L.S.D 5%. Significant differences (p<0.001) were realized both in the fields (plant height, dry shoot biomass yield, grain yield, field Striga count, and Striga damage ratings) and in the AG experiment with respect to maximum germination distance and numbers of induced germinated Striga seeds. Among the sorghum genotypes evaluated, T53B, N57, N68, C26, IESV 92036-SH, T30B, and Uyoma 47 white genotypes had stable yields under Striga infestation in the two sites whereas Nyadundo1, Nyadundo 2, and Uyoma 8 were susceptible. In the AG experiment, E117B, T30B, Uyoma 8, Uyoma 42 STR, and T53B induced high numbers of germinated Striga seeds with maximum germination distances (MGD). In contrast, Uyoma 47 Brown, IESV 92038/2-SH, and IESV 92036-SH sorghum genotypes induced the germination of few Striga seeds with low MGD. This study has identified and selected four Striga tolerant (T53B, N68, N57, and T 30B) and three resistant ( C 26, Uyoma 47 Brown, and IESV 92036-SH) sorghum genotypes which can be utilized in further research programs or adopted to improve sorghum productivity in the highly Striga infested regions of western Kenya.