Genetics of Fusarium head blight resistance in barley and of rust resistance in the wild wheat relative Aegilops longissima

Abstract

The use of crop wild relatives, landraces, unadapted accessions, and/or diverse panels of germplasm for discovery and deployment of disease resistance genes and/or alleles is extremely valuable in breeding crop varieties to changing disease pressures. This thesis explores two diverse germplasm panels for disease resistance in distinct pathosystems: quantitative resistance to Fusarium head blight (FHB) in barley and qualitative resistance to rust pathogens in a wild wheat relative. Fusarium head blight (FHB), a devastating disease of barley caused primarily by the fungus Fusarium graminearum, causes significant yield losses and grain contamination with mycotoxins. Enhancing resistance to FHB and the resultant accumulation of mycotoxins, such as deoxynivalenol (DON), is one of the most effective and economical methods of reducing losses caused by this disease. A diverse panel of 234 barley accessions from world-wide origins was assembled to assess the most promising FHB resistant germplasm and perform a genome-wide association study (GWAS) for FHB/DON. Multiple FHB and DON quantitative trait loci (QTL) were detected, some independent of QTL influencing heading date and plant height. These significant marker-trait associations were used to generate multi-marker haplotypes. Haplotype-trait associations were tested to analyze their diversity and effects within the panel. The rust diseases are major limiting factors in worldwide wheat production. These diseases include leaf rust caused by Puccinia triticina (Pt), stem rust caused by P. graminis f. sp. tritici (Pgt), and stripe rust caused by P. striiformis f. sp. tritici (Pst). Aegilops longissima, a wild grass closely related to the D subgenome of modern bread wheat, has been shown to carry resistance to rust and other diseases, although it remains underutilized as a resource for discovery of novel rust resistance genes. A panel of 404 Ae. longissima accessions was evaluated for resistance to several races of Pt, Pgt, and Pst. GWAS was conducted to map rust resistance loci. Nine key candidate markers were identified as promising for further investigation due to their detection via multiple GWAS models and/or their association with resistance to more than one pathogen race. The novel resistance loci identified will provide additional diversity available for use in wheat breeding.