Screening of selected wheat (triticum aestivum l.) lines for resistance and stem rust (puccinia graminis f.sp. tritici) race identification in Nakuru County, Kenya

Abstract

Wheat (T riticum aestivum L.) is one of the major cereals in Kenya, yet its production remains below national demand due to the stem rust disease. The evolution of Ug99 race evident with the emergence of aggressive races such as TTKTT has rendered more cultivars susceptible. The studies aimed at identifying spring wheat lines with adult and seedling plant resistance to wheat stem rust and also identify wheat stem rust races in Njoro and Mau-Summit in Nakuru County, Kenya. The field experiment was conducted at the Kenya Agriculture and Livestock Research Organization (KALRO), Njoro disease screening field in a l2><l2 partially balanced lattice design. Area Under Disease Progress Curve (AUDPC), Coefficient of infection (CI), and the final disease severity (FDS) were used as a measure of adult plant resistance (APR). 54.9 % of genotypes with AUDPC of 5200, 52.8 % with CI of 520, and 60.42 % with FDS of 530 was resistant. Effects due to season, genotype, and genotype-by-season interaction were significant (p§0.00l) for plant height, 1000-kernel Weight (TKW), biomass, and AUDPC. Mean grain yield and TKW ranged from 0.8 t ha'l to 9.05 t ha] and 20.03 g to 46.42 g, respectively. Genotypes 6022, 6095, 6096, 6107, 6134, 6136, 6137, 6138, and 6139 were found to possess APR and be high-yielding. For these edling experiment, the lines were inoculated with stem rust race TTKTT at two-leaf stage. The infection type Was scored 14 days post inoculation. One hundred and four genotypes were resistant with a score of 52. The lines identified for APR had a score of ‘0’, hence can progress to national performance trials. Bulk stem rust spores collected from Njoro and Mau-Summit were purified to obtain single pustules, which were then inoculated onto a 20 North American stem rust differential set at 7 days. The infection types were determined 14 days post-inoculation. Isolates from both sites had stem rust race TTKTT, a Ug99 variant virulent to genes Sr24, Sr3I, and SrTmp present in most Kenyan Wheat cultivars. This calls for the incorporation of new genes like Sr22, Sr26, Sr36, Sr4 7, Sr5 7 and SrND643 that were identified as resistant in both SPR and APR into the already adapted Kenyan Wheat cultivars.