Abstract:
Stem rust (Puccinia graminis f. sp. tritici) is one of the most important diseases of wheat
(Triticum aestivum L.) and is known to cause major wheat yield losses in Kenya as well as other wheat growing countries of Africa and Asia. The present study aimed at; i) determining seedling, adult plant resistance and yield of 64 advanced wheat breeding lines, and ii) estimating the kind of gene action in inheritance of adult plant resistance to stem rust and yield components in a 66 diallel cross of Kenyan wheat. The seedling resistance of the lines was evaluated in a greenhouse at the Kenya Agricultural and Livestock Research Organization, Njoro under artificial inoculation, while the adult plant resistance and yield were assessed across three different locations in Kenya, i.e. Njoro, Timau and Mau Narok. The seedling infection type (IT) was determined following a procedure based on a “0” to “4” scale. The Area Under Disease Progress Stairs (AUDPS), the Coefficient of Infection (CI) based on the field disease reactions and yield performances across sites were also used to compare the genotypes. Among the
screened genotypes, 39% exhibited resistance (IT‟s of “;”, “1”, “2” or combinations), 2% were intermediates and the rest (59%) showed susceptible reaction. There was a significant (P < 0.05) genotype, location and genotype x location interaction for AUDPS, CI and yield. Grain yield across sites was linearly and inversely related to CI and AUDPS with correlation values of; -0.87 for CI and -0.69 for AUDPS. Considering the adult plant disease response and yield potential, KSL 42 and KSL 3 consistently ranked among the top performers. These genotypes can therefore be utilized in Kenyan wheat breeding programs for improvement of yield and stem rust resistance with emphasis on adult plant resistance. Results of genetic analysis revealed that both general combining ability (GCA) and specific combining ability (SCA) effects were significant (P < 0.05) for all traits studied. However, the GCA effects were predominant. Additionally, the covariance/ variance (Wr/Vr) graph revealed partial dominance for stem rust infection, the number of days to heading and the number of productive tillers. Over-dominance was displayed for grain yield and plant height. Inclusion of parents KSL 13 and KSL 42 as well as crosses KSL 34/KSL 52, NjBw II/KSL 42, Kwale/KSL 13, KSL 34/KSL 42 in a breeding program would produce desired segregants. These could therefore be exploited successfully in enhancement of stem rust disease resistance as well as yield in areas prone to stem rust infection. The desirable alleles in these different sources can be accumulated by gamete selection.
