Exploration and Exploitation of Disease Resistance in Ryegrass

Resistance to major diseases such as crown rust (caused by Puccinia coronata; Puc) or bacterial wilt (caused by Xanthomonas  translucens pv. graminis; Xtg)  is a major target in any breeding program of ryegrasses (Lolium spp.). The aim of our research is to elucidate the genetic control of disease resistance and to develop and apply molecular genetic tools to improve resistance breeding of ryegrasses. Based on a bi-parental mapping population, we were able to identify major QTL for bacterial wilt and crown rust resistance based on a single Xtg isolate and a spore mixture of naturally occurring Puc isolates. QTL for crown rust resistance were partially confirmed in a different, independent mapping population and using spore mixtures as well as single spore isolates. A single marker linked to the major crown rust QTL on LG1 was used for a proof of concept study on marker assisted selection. Donor plants carrying the desired marker allele were crossed with susceptible ecotypes, individuals homozygous for marker allele were selected,  interpollinated and the progeny phenotyped for resistance. Resistance to crown rust was significantly increased when compared to populations subjected to just phenotypic and not marker assisted selection, demonstrating the desired effect of the marker allele. In order to further characterize genes controlling resistance, we have performed mapping-by-sequencing in the initial  L. multiflorum population. Furthermore, we have taken advantage of an association population that has been densely genotyped via sequencing to identify further candidate genes controlling resistance. Potential candidates included Xa5, Lr10 or a CCR4-like gene.