Genetic analysis of leaf and stripe rust resistance in the spring wheat (Triticum aestivum L.) cross RL4452/AC Domain

Abstract

Leaf rust and stripe rust of wheat (Triticum aestivum L.) are caused by the fungal pathogens Puccinia triticina, and Puccinia striiformis f.sp. tritici, respectively. In North America, the incorporation of adult-plant resistance (APR) genes into breeding lines has been an important strategy to achieve durable resistance to both diseases. Previously, the spring wheat cultivar AC Domain was reported to express an effective level of adult-plant resistance (APR) to leaf rust under field conditions. Early gene postulation work had suggested AC Domain might carry the APR gene Lr34 due to its phenotypic similarity to other Lr34 carrying lines. However, new gene specific markers have shown that AC Domain is not a carrier of Lr34. The objective of this research was to genetically localize the resistance in AC Domain, which is important because the cultivar has frequently been used as a parent in Canadian breeding programs, primarily for its value as a source of pre-harvest sprouting resistance. A mapping population of 185 doubled haploid (DH) lines derived from the cross ‘RL4452’ by ‘AC Domain’ was used for this study. RL4452 is a known carrier of Lr34. During 2011-2012, the DH population was evaluated in field leaf rust nurseries at Saskatoon, SK and Portage, MB and at a stripe rust nursery at Lethbridge, AB. Field results indicated that rust resistance in the mapping population was variable, with lines ranging from highly resistant, to highly susceptible. DH lines carrying Lr34 showed a high level of resistance to both diseases. Thus, the non-Lr34 carriers were genotyped using select SSR markers, and by an Illumina 9k Infinium iSelect SNP assay for subsequent quantitative trait loci (QTL) analysis. QTL analysis revealed that AC Domain donated a major resistance QTL located on chromosome 2BS, that mapped 46 cM proximal to markers linked to Lr16, and explained a significant portion of the leaf and stripe rust phenotypic variance in all test environments. In addition, this QTL was significantly associated with the expression leaf tip necrosis (LTN), reduction in area under the disease progress curve (AUDPC), and coefficient of infection (CI). In certain environments the interaction between the 2B QTL and Lr34 was additive resulting in a superior level of rust resistance. Indoor rust testing showed AC Domain was susceptible to both diseases at the seedling stage. Taken together these results suggest that the identified resistance in AC Domain is likely due to the presence of an APR gene, on chromosome 2BS.