Genetic dissection of nonhost resistance to wheat stem rust in Brachypodium distachyon

Authors: DELLA COLETTA, RAFAEL - University Of Minnesota; HIRSCH, CANDICE - University Of Minnesota; ROUSE, MATTHEW - University Of Minnesota; LORENZ, AARON - University Of Minnesota; Garvin, David

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2018
Publication Date: 4/1/2019
Citation: Della Coletta, R., Hirsch, C.N., Rouse, M.N., Lorenz, A., Garvin, D.F. 2019. Genetic dissection of nonhost resistance to wheat stem rust in Brachypodium distachyon. Molecular Plant-Microbe Interactions. 32(4):392-400. https://doi.org/10.1094/MPMI-08-18-0220-R.
DOI: https://doi.org/10.1094/MPMI-08-18-0220-R

Interpretive Summary: Stem rust is a damaging disease of wheat and other grass crops. New forms of stem rust have emerged in Africa that overcome most of the known stem rust resistance genes in wheat. While new resistance genes have been identified, some have already been overcome by the disease. An alternative approach for controlling stem rust in wheat is to introduce a new layer of stem rust resistance by introducing genes that control nonhost resistance to wheat stem rust. Nonhost resistance is the reason that most crops are not infected by most diseases. This form of resistance is considered robust and unlikely to be overcome by the disease. However, the genetic control of nonhost resistance is not well understood. Using molecular genetics and genomics methods, the genetics of nonhost resistance in Brachypodium, a small grass related to wheat and a nonhost to wheat stem rust, was determined. Six separate regions on three different Brachypodium chromosomes were found to contribute to nonhost resistance to wheat stem rust. The amount of resistance that each region contributed to the resistance varied, but together they accounted for the majority of the observed nonhost resistance to wheat stem rust. Some of these regions contain very few genes, permitting the identification of potential genes involved in the nonost resistance response. These findings provide a starting point to isolate the genes for nonhost resistance to wheat stem rust. When these are then introduced into wheat, they may provide a unique and long-lasting level of resistance to stem rust. This will protect the world’s wheat supply from stem rust, and in turn will enhance global food security.

Technical Abstract: The emergence of new races of Puccinia graminis f.sp. tritici (Pgt), the causal pathogen of wheat stem rust, has spurred interest in developing durable resistance to this disease in wheat. Nonhost resistance holds promise to help control this and other diseases because it is durable against non-adapted pathogens. However, the genetic and molecular basis of nonhost resistance to wheat stem rust is poorly understood. In this study, the model grass Brachypodium distachyon (Brachypodium), a nonhost of Pgt, was used to genetically dissect nonhost resistance to wheat stem rust. A recombinant inbred line (RIL) population segregating for response to wheat stem rust was evaluated for resistance. Evaluation of genome-wide cumulative SNP allele frequency differences between contrasting pools of resistant and susceptible RILs, followed by molecular marker analysis, identified six quantitative trait loci (QTL) that cumulatively explained 72.5% of the variation in stem rust resistance. Two of the QTLs explained 31.7% of the variation, and their interaction explained another 4.6%. Thus, nonhost resistance to wheat stem rust in Brachypodium is genetically complex, with both major and minor QTLs acting additively and, in some cases, interacting. These findings will guide future research to identify genes essential to nonhost resistance to wheat stem rust.