Abstract:
Stem rust (Puccinia graminis f.sp. tritici- Pgt) disease is currently one of the major biotic constraints in wheat (Triticum aestivum) production worldwide. Access to diverse sources of genetic resistance is important in building a broad base resistance to stem rust in our commercial wheat varieties. The obejectives of this study were (i) to screen wheat genotypes from diverse origins for both seedling (SPR) and adult plant resistance (APR) to the predominant Ug99 race and its variants in Kenya, and (ii) to determine the mode and number of genes conferring resistance to TTKST race in the identified resistant lines. Screening for seedling plant resistance (SPR) was done under controlled greenhouse conditions while screening for adult plant resistance (APR) was done in the field at KALRO-Njoro, Kenya during 2012 and 2013 wheat growing seasons. Selection for APR was based on area under disease progress curve (AUDPC, <300) and coefficient of infection (CI, <20) values. Under field testing, there were variations in the disease severities and responses within and between seasons. AUDPC values ranged from 0 to 1,285; CI values from 0 to 100 and final disease severities (FDS) from 0 to 100S. This study identified potential sources of adult plant (119 i.e 35%) and seedling (125 i.e 37% -TTKSK, 137 i.e 40% -TTKST) resistance against stem rust Ug99 races. Genotypes KSL18, PCB52, PCB62, PCB76, Bounty, Lenana, K6290 Bulk, Kenya Swara, and Kenya Nyati have both resistance genes. In the second experiment, the resistant wheat genotypes KSL18, PCB52, PCB62 and PCB76 were crossed with known susceptible cultivars Kwale and Duma. The resulting hybrids and F2 populations alongside the parents were then tested in the greenhouse for response to the stem rust race TTKST. The selected wheat lines exhibited infection types ‘;’ to ‘2’ depicting resistance while Kwale and Duma depicted infection type ‘3+’ to TTKST. Evaluation of F2 populations that derived from Kwale × PCB52 indicated that the resistance is conferred by a single dominant gene (3R:1S ratio). However, all other F2 populations showed that resistance was conferred by two genes complementing each other (duplicate recessive epistasis) thus the ratios 9R: 7S. These identified resistant genotypes could be evaluated for other qualities and passed as potential varieties or used as sources of valuable resistance to achieve durable resistance against stem rust races.
