Characterization of stem rust resistance in old tetraploid wheat landraces from the Watkins collection

Abstract

Stem rust is one of the important diseases of tetraploid wheats worldwide. One hundred and five landraces from the Watkins collection were assessed for seedling and adult plant stem rust response variation. Seedling resistance genes Sr8a, Sr8b, Sr9e, Sr9g, Sr12, Sr13, Sr17 and Sr23 were postulated in 28 genotypes using Australian and Indian Puccinia graminis f. sp. tritici pathotypes. Four genotypes possessed either uncharacterized seedling stem rust resistance gene(s) or combinations of known stem rust resistance genes with compensating avirulences among pathotypes used. Adult plant stem rust response assessments were made on 73 seedling susceptible genotypes in Australia and Ethiopia. Adult plant stem rust responses varied from 1 (very resistant) to 7 (moderately susceptible) on a 1–9 scale. The Ethiopian nursery was exposed to Ug99 (TTKSK) and JRCQC (virulent on Sr9e and Sr13). Some genotypes that exhibited high responses in Australia were scored low in Ethiopia. These results demonstrated the effectiveness of some resistance gene(s) that were ineffective in Australia. The opposite trend was also noted. Over 50 % genotypes exhibited commercially acceptable rust responses varying between 2 and 5 across sites and years. Genotyping with the Sr2-linked molecular marker csSr2 did not detect Sr2 in any of the genotypes. The marker gwm533 however detected the presence of Sr2 in eight genotypes. Stem rust resistant genotypes that carried varying levels of APR could carry new genes. Genetic analysis and deployment of these uncharacterized sources of seedling and APR in new cultivars will ensure durable stem rust control through increased diversity.