Studies of the Wheat-rust Disease Pathosystem with a Focus on Resistance Gene Characterisation

Abstract

Wheat is one of the first domesticated and cultivated crops together with barley. Rust diseases are considered as one of the major threats to wheat production in almost all of the wheat growing areas worldwide and disease control relies mainly on the utilisation of genetic resistance. The general objective of this doctoral study is to reduce the risk of yield loss due to rust diseases by providing genetic knowledge on wheat-rust pathosystems at the molecular level. In this thesis, integrated efforts have been devoted to i: understand rust pathogen populations at the molecular level; ii: characterise genetic resistance in the host; iii: understand the functional mechanisms underlying the plant-microbial interaction; and iv: to inform the effective deployment of characterised genetic resistance. In Chapter 3, the relationship between virulence and molecular patterns using SSR markers on selected isolates of Puccinia graminis f. sp. tritici (Pgt) collected in Australia during a 52 year period was examined and an evolutionary pathway involving these isolates was proposed. In Chapter 4 and 5, I focused on the stem rust resistance locus Sr26, derived from Thinopyrum ponticum (tall wheat grass), as an excellent example of the successful utilisation of genetic resistance from a wild relative of a crop plant that remains one of the few durable sources of resistance currently effective against all known field isolates of Pgt. I undertook the cloning of Sr26 by MutRenSeq pipeline. A candidate gene of Sr26 was successfully identified and I demonstrated that this gene candidate encoded a CNL (CC-NB-ARC-LRR) type of R protein. In Chapter 6, candidate genes were successfully identified for the stripe rust resistance genes Yr7, Yr5, and YrSP. Chapter 7 comprised the addendum of Chapter 6, the complementary transgenic validation for Yr5 and YrSP were provided.