Abstract
Barley ‘Scald’ is an economically damaging fungal disease that is a global problem, causing significant yield and economical losses in the UK barley feed and malting industries. Presently, a limited number of Rhynchosporium resistance genes exist, but selective pressures on the fungi cause the demand for new sources of resistance. Landraces, such as the Scottish Bere barley, hold potential sources of resistance that can be utilised, with farmers providing anecdotal evidence of resistance in field populations of Bere. This study analysed 131 heritage cultivars and landrace lines, including 37 Bere lines, to screen for resistance using both detached leaf assays (DLAs) and field experiments. Results showed that Bere lines produced smaller, but more necrotic, lesions for the majority of isolates in the DLAs, as well as smaller scores when visually assessed in field conditions. Whilst the infection patterns of the lines differed between isolates and experimental conditions, three Bere lines were identified as consistently showing reduced levels of infection (45 A 23, 58 A 36 Eday, and 8-125). Using genome-wide association analysis, we were able to identify a number of genomic regions associated with reduced infection symptoms, four in regions associated with known resistance genes, but another four associated with new regions that contain promising candidate genes. Further analysis of these new regions and candidate genes should be undertaken to identify targets for future disease-resistance breeding.
Highlights
The Rhynchosporium genus comprises of haploid hemibiotrophic fungi that infect grasses such as rye (Secale cereale), triticale (× Triticosecale spp.), and barley (Hordeum vulgare)
Significant differences in lesion severity were not observed between sub-categories (p = 0.066), but were in the variate interaction (p = 0.048) that showed that the Bere lines exhibited greater severity with isolates L2A and 13-13 (Fig. 1b)
Barley scald caused by the fungal pathogen Rhynchosporium commune is a disease of global significance, and a major problem in most parts of the UK (Avrova and Knogge 2012)
Summary
The Rhynchosporium genus comprises of haploid hemibiotrophic fungi that infect grasses such as rye (Secale cereale), triticale (× Triticosecale spp.), and barley (Hordeum vulgare). A study by Zaffarano et al (2011) identified that the pathotype infecting barley. UK was a separate species, and it was subsequently labelled as Rhynchosporium commune. This host adaptation is mediated through effector proteins that stall the development of the fungi in planta in order to extend the biotrophic phase (Clark et al 2008; Penselin et al 2016). Yield losses have been reported ranging from 10 to 45%, and economic yield is reduced due to inferior quality grain for products such as malting barley (Avrova and Knogge 2012). In the UK, this equates to an estimated £7.2 million worth of losses in barley after fungicide treatments (Paveley et al 2016)
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