Elucidating the molecular genetics of host and nonhost resistance in barley to stripe rust

Plants have a remarkable ability to resist the majority of pathogenic microbes they encounter. As such, they are described as nonhosts. Nonhost resistance is often conceptualised as a qualitative separation from host resistance. Classification into these two states is generally facile, as they fail to fully describe the range of states that exist in the transition from host to nonhost. This poses a problem when studying pathosystems that cannot be classified into either of these categories due to their intermediate status relative to the two extremes. Therefore, the terms intermediate host and intermediate nonhost have been proposed to describe pathosystems in the evolutionary transition between host and nonhost status. At present, a significant amount of research exists into the molecular genetics of host and nonhost pathosystems but very little is known about intermediate systems. The work in this Ph. D. thesis focuses on the interaction of barley with Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust, as an intermediate host pathosystem. The first research chapter describes the development of two microscopic phenotypic assays used to quantify P. striformis f. sp. tritici in barley leaves challenged with the pathogen. These assays are then used to screen a large panel of barley accessions to define the intermediate host status of barley relative to a host pathosystem. Subsequently, these assays play a key role in determining that the genetic architecture of resistance in barley is underpinned by three major effect resistance loci: Rpst1, Rpst2, and Rpst3. Using a combination of classical map-based genetics and contemporary genomics information I identify a candidate NLR gene underlying Rpst2 resistance on chromosome 7HL. Furthermore, I show that distinct genes condition host and nonhost resistance in barley by mapping the host resistance gene, rps2 to chromosome 2HL.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2015

Author dc:creator

• Dawson, Andrew

Language dc:language

en