Mapping of Disease Resistance Loci in Barley on the Basis of Visual Assessment of Naturally Occurring Symptoms

Abstract

Using field-scored data of disease severity under natural infestation, we mapped loci affecting resistance to powdery mildew (Blumeria graminis DC f. sp. hordei ~m. Marchal), leaf rust (Puccinia hordei Otth.), stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn.), scald [Rhynchosporium secalis (Oudem.) J.J. Davis], and net blotch (Pyrenophora teres Drechs.). The mapping population included parents and doubled-haploid progeny of the two-row barley cross Harrington/TR306. Resistance was affected by two to five loci, explaining 8 to 45% of the phenotypic variance, per disease. All chromosomes, except chromosome 5 (1H), contained regions with at least one disease resistance locus. One region on chromosome 4 (4H) contributed to resistance to stem rust, scald, and net blotch. This region has previously been reported to affect days to heading and maturity. Two known resistance genes in the population, Rpgl and Mlg, were mapped to within 3 centimorgans (cM) of their previously estimated genomic locations by simple interval mapping of the field-scored data. This indicates that the genomic positions of disease resistance genes can be estimated accurately with simple interval mapping, even on the basis of field-scored data. G ENETIC RESISTANCE is an ecologically and economically sound approach to disease control in crops and is a common and important objective of barley (Hordeum vulgare L.) breeding. Breeders and pathologists select plants or lines with complete or partial disease resistance. They commonly make selections based on the results of artificially inoculated trials, on visual assessments of naturally occurring disease symptoms, or both. Plants or lines may be qualitatively classified as either resistant or susceptible. The examination of disease response may also involve the quantitative assessment of continuous variation in plant response to disease infestation. Both qualitative and quantitative data may be used to map resistance loci relative to molecular and/or morphological markers in plant genomes. With qualitative data, classical linkage mapping may be used to map genes with major effects on disease resistance. With quantitative data, quantitative trait locus (QTL) analysis may be used to detect chromosome regions that contribute to disease resistance.

Identification of QTLs for powdery mildew and scald resistance in barley

“…It occurred in the 'Igri' × 'Danilo' cross (Backes et al, 1995), and in the Harrington × TR306 cross (Spaner et al, 1998). In conclusion, all the QTLs for PR against scald detected in the present L94 × 'Vada' cross are supported by previously mapped QTLs in various barley populations.…”

“…The fact that they were detected in both years lends confidence to the reliability of these QTLs. The other QTL, Rbgq3, mapped at 130 cM from the tip of the short arm on chromosome 7 (5H) and is at a similar position as a QTL reported by Spaner et al (1998) andby Saghai Maroof et al (1994). It is possible that some other QTLs for powdery mildew resistance with smaller effects were not identified due to the small population size (51 RILs) and the low level of infection and, as a consequence, the modest contrast in infection severity between the RILs.…”

“…QTL Rrsq1 may be the same as the QTL detected in the Ingrid × Abyssinian since both Abyssinian and L94, also known as Abyssinian 1102, are of Ethiopian origin (Jørgensen, 1992). QTL Rrsq2 on chromosome 4 (4H) may correspond to the QTL for scald resistance detected in the Harrington × TR306 cross with the resistance allele contributed by TR306 (Spaner et al, 1998). In our population the confidence interval of Rrsq2 contained the locus mlo.…”

“…It occurred in the Blenheim × E224/3 cross with the resistance allele contributed by E224/3 (Thomas et al, 1995), in the Harrington × TR306 cross with the resistance allele contributed by Harrington (Spaner et al, 1998), and in the Ingrid × Abyssinian cross with the resistance allele contributed by Abyssinian (Grønnerød et al, 2002). QTL Rrsq1 may be the same as the QTL detected in the Ingrid × Abyssinian since both Abyssinian and L94, also known as Abyssinian 1102, are of Ethiopian origin (Jørgensen, 1992).…”

Fine mapping, physical mapping and development of diagnostic markers for the Rrs2 scald resistance gene in barley

“…spontaneum Rrs12 on 7HS, Rrs13 on 6HS, Rrs14 on 1HS, and Rrs15 on 7HL (Abbott et al 1992;Abbott et al 1995;Garvin et al 1997;Garvin et al 2000;Genger et al 2003a;Genger et al 2003b;Genger et al 2005), or from Hordeum bulbosum Rrs16 on 4HS (Pickering et al 2006). Furthermore, a number of QTL studies revealed QTLs for scald resistance on several chromosomes whose loci often coincided with locations of known scald resistance genes (Backes et al 1995;Bjørnstad et al 2004;Cheong et al 2006;Genger et al 2003;Grønnerød et al 2002;Spaner et al 1998;Thomas et al 1995;von Korff et al 2005;Wagner et al 2008;Yun et al 2005).…”