Identification of QTLs conferring resistance to scald (Rhynchosporium commune) in the barley nested association mapping population HEB-25

Abstract

Background Barley scald, caused by the fungus Rhynchosporium commune, is distributed worldwide to all barley growing areas especially in cool and humid climates. Scald is an economically important leaf disease resulting in yield losses of up to 40%. To breed resistant cultivars the identification of quantitative trait loci (QTLs) conferring resistance to scald is necessary. Introgressing promising resistance alleles of wild barley is a way to broaden the genetic basis of scald resistance in cultivated barley. Here, we apply nested association mapping (NAM) to map resistance QTLs in the barley NAM population HEB-25, comprising 1420 lines in BC1S3 generation, derived from crosses of 25 wild barley accessions with cv. Barke. Results In scald infection trials in the greenhouse variability of resistance across and within HEB-25 families was found. NAM based on 33,005 informative SNPs resulted in the identification of eight reliable QTLs for resistance against scald with most wild alleles increasing resistance as compared to cv. Barke. Three of them are located in the region of known resistance genes and two in the regions of QTLs, respectively. The most promising wild allele was found at Rrs17 in one specific wild donor. Also, novel QTLs with beneficial wild allele effects on scald resistance were detected. Conclusions To sum up, wild barley represents a rich resource for scald resistance. As the QTLs were linked to the physical map the identified candidate genes will facilitate cloning of the scald resistance genes. The closely linked flanking molecular markers can be used for marker-assisted selection of the respective resistance genes to integrate them in elite cultivars.

Pyramiding of scald resistance genes in four spring barley MAGIC populations

“…The recurrent parent in HEB-25 is ‘Barke’, which was crossed with 25 wild barley ( H. spontaneum ) accessions from the fertile crescent and thus having clearly higher amount of diversity introduced in their material compared to ours. Interestingly, out of the eight QTL Büttner et al ( 2020 ) found two others in addition to QRs7H.2, which are potentially the same as ours: the one considered as Rrs1 on chromosome 3H and possibly the QTL on 6H at 18.9Mbp.…”

“…The other QTL detected in MAGIC 4 in our study had its peak marker on the long arm of chromosome 7H at 635.2 Mb, which is close to Rrs15 located at 647.6 Mb (Genger et al 2003). An even closer QTL is the recently reported new QTL QRs7H.2 624.2 Mb, which was found by Büttner et al (2020) in a barley nested association mapping population, HEB-25 (Maurer et al 2015). QTL close to the significant marker can be considered as very relevant candidates.…”

Genome-Wide Association Study for Resistance to Rhynchosporium in a Diverse Collection of Spring Barley Germplasm

“…These studies used three, five, and two field trials, respectively, for their GWAS analysis. A further eight QTL originating from wild barley accessions were identified by GWAS in the Nested Association Mapping population HEB-25 [21]. GWAS was also used to map nine rhynchosporium resistance regions, including three new regions, in four multi-parent advanced generation inter-cross (MAGIC) populations tested in northern Europe [22].…”

Identifying potential novel resistance to the foliar disease ‘Scald’ (Rhynchosporium commune) in a population of Scottish Bere barley landrace (Hordeum vulgare L.)

“…Currently, a limited number of resistance genes in barley against R. commune have been identified, with Rrs18, found on chromosome 6HS by Hofmann (2014) and confirmed by Coulter et al (2018) being the most recently reported. A number of these Rrs genes originate from landraces (Bjørnstad et al 2004;Hanemann et al 2010;Hofmann et al 2013). It is suggested that Scandinavian and other northern European landraces might be a prime source for resistance to rhynchosporium as it is speculated that R. commune originated in this area providing diverse R. commune populations and the longest period of landrace selection for rhynchosporium resistance (McDonald 2015), suggesting the Scottish barley landrace population 'Bere' as a suitable candidate.…”