The ENHANCED MAGNAPORTHE RESISTANCE 1 locus affects Ramularia leaf spot development in barley

Abstract

Ramularia leaf spot (RLS) is a newlyimportant disease of barley which is caused when the fungus Ramularia collo-cygni enters necrotrophic development during colonisation of the host. Mutant alleles at the barley MILDEW LOCUS O, mlo, locus confer broad spectrum durable resistance against the powdery mildew fungus, Blumeria graminis f. sp. hordei, but can enhance susceptibility to pathogens with necrotrophic development stages such as R. collo-cygni. Given the importance of mlo in spring barley breeding programmes, identifying loci that mitigate the effect of mlo-mediated susceptibility on necrotrophic disease development is an important target. Mutation of the ENHANCED MAGNAPORTHE 1 (emr1) locus which can affect mlo-associated disease susceptibility, leads to a reduction in RLS symptoms on barley leaves but does not reduce R. collo-cygni accumulation. The effect of emr1 on the transition of R. collo-cygni from endophyte to necrotroph may relate to changes in reactive oxygen species in mutant plants which show reduced sensitivity to chloroplastic superoxide induced cell death and has lower relative chlorophyll content compared to mlo plants.

Biosynthesis of Rubellins in Ramularia collo-cygni—Genetic Basis and Pathway Proposition

“…To date, no source of genetic resistance has been identified in barley; however, the genetic background of the host is known to play a role in disease development as varieties carrying the mildew locus O ( mlo ) mutation, which confers resistance to powdery mildew, exhibit increased susceptibility to RLS [ 13 ]. Further supporting the role of the host genetic background in RLS development, a loss of function mutation of the Enhanced Magnaporthe 1 ( emr1 ) gene in a mlo background mitigates the effect of the mlo mutation on RLS severity leading to decreased RLS symptoms [ 14 ].…”

Detection of Ramularia collo-cygni DMI- and SDHI-resistant field populations in Austria and the effect of fungicides on the population and genetic diversity

“…mildew resistance locus 0 (MLO) genes are used in breeding new varieties for powdery mildew resistance but these genes have no effect on R. collo-cygni in grain (Hofer et al, 2015). Another study by McGrann et al (2020) concluded that the Enhanced Magnaporthe Resistance locus (EMR1) reduce RLS development. Additionally, only a few data of quantity of sporulation between different varieties (Hoheneder et al, 2021) or different culture parameters like light or nutrients are available.…”