Multi-Trait and Multi-Environment QTL Analyses for Resistance to Wheat Diseases

BACKGROUND: Stripe rust, leaf rust, tan spot, and Karnal bunt are economically significant diseases impacting wheat production. The objectives of this study were to identify quantitative trait loci for resistance to these diseases in a recombinant inbred line (RIL) from a cross HD29/WH542, and to evaluate the evidence for the presence loci on chromosome region conferring multiple disease resistance. METHODOLOGY/PRINCIPAL FINDINGS: The RIL population was evaluated for four diseases and genotyped with DNA markers. Multi-trait (MT) analysis revealed thirteen QTLs on nine chromosomes, significantly associated with resistance. Phenotypic variation explained by all significant QTLs for KB, TS, Yr, Lr diseases were 57%, 55%, 38% and 22%, respectively. Marginal trait analysis identified the most significant QTLs for resistance to KB on chromosomes 1BS, 2DS, 3BS, 4BL, 5BL, and 5DL. Chromosomes 3AS and 4BL showed significant association with TS resistance. Significant QTLs for Yr resistance were identified on chromosomes 2AS, 4BL and 5BL, while Lr was significant on 6DS. MT analysis revealed that all the QTLs except 3BL significantly reduce KB and was contributed from parent HD29 while all resistant QTLs for TS except on chromosomes 2DS.1, 2DS.2 and 3BL came from WH542. Five resistant QTLs for Yr and six for Lr were contributed from parents WH542 and HD29 respectively. Chromosome region on 4BL showed significant association to KB, TS, and Yr in the population. The multi environment analysis for KB identified three putative QTLs of which two new QTLs, mapped on chromosomes 3BS and 5DL explained 10 and 20% of the phenotypic variation, respectively. CONCLUSIONS/SIGNIFICANCE: This study revealed that MT analysis is an effective tool for detection of multi-trait QTLs for disease resistance. This approach is a more effective and practical than individual QTL mapping analyses. MT analysis identified RILs that combine resistance to multiple diseases from parents WH542 and/or HD29

Distribution of races and Tox genes in Pyrenophora tritici-repentis isolates from wheat in Argentina

Tan spot, caused by Pyrenophora tritici-repentis, is a common disease in wheat-growing regions of Argentina. In this study 65 isolates of P. tritici-repentis obtained from different cultivars and wheat regions of Argentina were assessed for their virulence on six wheat cultivars/lines (Glenlea, Salomouni, Katepwa, M-3, 6B365 and 6B662) and for the presence/absence of the Tox genes based on a PCR approach. Thirty-six isolates were assigned to races, of which races 4 and 8 were dominant. Results for molecular analysis of ToxA, ToxB, ToxB-like and toxb genes showed that 57 isolates possessed the ToxA gene whereas only one isolate possessed ToxA and ToxB genes. There was no correlation between races and the toxin genotypes. It is suggested that P. tritici-repentis exhibits a complex race structure in Argentina