Abstract:
Wheat (Triticum aestivum L.) stem rust (Puccinia graminis f.sp tritici) is destructive and can lead to total yield loss in susceptible wheat varieties. The Objectives of this study were to determine the gene action, the nature of inheritance controlling stem rust adult plant resistance, and to evaluate the yield stability of wheat lines selected for resistance to stem rust for selected growing areas in Kenya. Two experiments were carried out. In the first experiment, six basic generations, P1, P2, F1, F2, BC1 and BC2 were developed in two cropping seasons, from crosses involving stem rust resistant and susceptible parents. Testing of the basic generations for resistance to stem rust was conducted in the field. The universally susceptible line, Cacuke was used as spreader in the experiment. Host response (infection type) to stem rust was based on the modified Cobb scale; resistant, moderately resistant, susceptible, moderately susceptible and combination of moderately resistant and moderately susceptible. The disease severity was recorded on scale of 0-100% where 0% is immune and 100% is completely susceptible. Scoring for stem rust began when the susceptible spreader depicted 50% severity. Three sets of data were observed at intervals of seven days. The second experiment had forty genotypes which were planted at Njoro, Kinamba, Olkalau and Eldoret in an alpha lattice design replicated three times. Data on yield and response to stem rust were observed. Statistical analyses were done using Genstat computer software. Results of the first study indicated that stem rust resistance is highly controlled by additive genes and is highly inheritable, with heritability ranging from 59% to 92%. This was an indication that more than 50% of the observed resistance is genetic hence it can be transmitted to the offspring. The results from multi-location trial identified genotypes G25, G18 and G29 with 2.07, 1.98 and 1.97 t ha-1 respectively, to be the best in yield performance. Genotypes G5, G16, G29, and G40 were highly stable for yield according to GGE biplot. Considering a combination of stem rust resistance and yield performance, genotypes G5, G16, G18, G24 and G36 were outstanding and hence, desirable candidates for future release.
