International Symposium on Cereal Leaf Blights 2019 | University College Dublin, Ireland | 22-24 May 2019

Genetic and environmental effects on resistance of barley to Ramularia leaf spot, and consequences for variety trialling

James Brown*
John Innes Centre

Neil Havis
Scotland's Rural College

Graham McGrann
Science and Advice for Scottish Agriculture

Joanne Russell
James Hutton Institute

Catherine Garman
Agriculture and Horticulture Development Board

Oral Presentation
Host Genetics and Resistance Breeding

Moore Auditorium, UCD O'Brien centre for Science
24 May 2019, 09:00

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Ramularia leaf spot (RLS) is a destructive, late-season disease of barley caused by the fungus Ramularia collo-cygni.  When it became commercially important in the late 1990s, the most RLS-susceptible barley varieties were those with mlo mildew-resistance1.  The genetic association between mlo and RLS-susceptibility was confirmed but there was a substantial environmental influence on the effect of mlo2.  Greater abiotic stress was found to increase RLS severity3.

There has been progress in breeding barley for RLS resistance1,4 but in field trials of a large set of spring barley varieties between 2010 and 2013, there was strong genotype-by-environment interaction (GxE) in RLS severity.  Similarly, in UK Recommended List trials, varieties’ scores at different sites have not always been consistent.  The contribution of various factors to GxE was analysed in variety trial data from 2017.  RLS is difficult to score accurately because it can be confused with several other syndromes4, and it was indeed found that different people do not score RLS in a comparable manner.  This effect was not as strong as that of GxE, however, because there was substantial variation between variety scores obtained by one experienced person.  Variation between sites is unlikely to result from variety-by-isolate specificity.

The use of sites where RLS is by far the predominant disease will enable breeders to continue advancing resistance by selecting select elite varieties which combine mlo for durable mildew resistance and minor genes dispersed throughout the genome for RLS resistance.  Further control of RLS may be advanced by understanding the factors which caused the fungus to change from an insignificant endophyte to an aggressive pathogen in the 1990s.

1Pinnschmidt & Sindberg 2009, Aspects Appl Biol 92:71–80

2McGrann et al. 2014, J Exptl Botany 65:1025-37

3McGrann and Brown 2018, Ann Botany 121:415-30

4Havis et al. 2015, Phytopathology 105:895-904