Identification of quantitative trait loci for resistance to two species of root-lesion nematode (Pratylenchus thornei and P. neglectus) in wheat

Abstract

Abstract. Pratylenchus thornei and P. neglectus are two species of root-lesion nematode that cause substantial yield losses in wheat. No commercially available wheat variety has resistance to both species. A doubled-haploid population developed from a cross between the synthetic hexaploid wheat line CPI133872 and the bread wheat Janz was used to locate and tag quantitative trait loci (QTLs) associated with resistance to both P. thornei and P. neglectus. Wheat plants were inoculated with both species of nematode in independent replicated glasshouse trials repeated over 2 years. Known locations of wheat microsatellite markers were used to construct a framework map. After an initial single-marker analysis to detect marker-trait linkages, chromosome regions associated with putative QTLs were targetted with microsatellite markers to increase map density in the chromosome regions of interest. In total, 148 wheat microsatellite markers and 21 amplified fragment length polymorphism markers were mapped. The codominant microsatellite marker Xbarc183 on the distal end of chromosome 6DS was allelic for resistance to both P. thornei and P. neglectus. The QTL were designated QRlnt.lrc-6D.1 and QRlnn.lrc-6D.1, for the 2 traits, respectively. The allele inherited from CPI133872 explained 22.0-24.2% of the phenotypic variation for P. thornei resistance, and the allele inherited from Janz accounted for 11.3-14.0% of the phenotypic variation for P. neglectus resistance. Composite interval mapping identified markers that flank a second major QTL on chromosome 6DL (QRlnt.lrc-6D.2) that explained 8.3-13.4% of the phenotypic variation for P. thornei resistance. An additional major QTL associated with P. neglectus resistance was detected on chromosome 4DS (QRlnn.lrc-4D.1) and explained a further 10.3-15.4% of the phenotypic variation. The identification and tagging of nematode resistance genes with molecular markers will allow appropriate allele combinations to be selected, which will aid the successful breeding of wheat with dual nematode resistance.Additional keywords: synthetic hexaploid wheat, doubled haploids, composite interval mapping. IntroductionTwo species of root-lesion nematode, Pratylenchus thornei Sher and Allen and P. neglectus (Rensch) Filipjev and Schuurmans Stekhoven, cause substantial yield losses in cereal crops throughout the world. High populations of P. thornei cause up to 85% yield loss in wheat (Triticum aestivum L.) varieties (Thompson et al. 1993). Similarly, P. neglectus causes up to 27% yield loss in wheat varieties (Taylor et al. 1999). In Australia, annual lost wheat production caused by P. thornei and P. neglectus is estimated at $36 million and $12 million, respectively (Brennan and Murray 1998).Glasshouse screening of wheat lines inoculated with pure cultures of nematodes has suggested that the genetic mechanisms that confer resistance to P. thornei do not confer resistance to P. neglectus (Farsi et al. 1995;Taylor et al.

Mapping quantitative trait loci for resistance to Pratylenchus thornei from synthetic hexaploid wheat in the International Triticeae Mapping Initiative (ITMI) population

“…Comparison of maps using common markers revealed that SSR marker locus Xbarc183 on chromosome 6DS was associated with resistance to P. thornei in this study as well as in a second mapping study in which resistance was contributed by a different synthetic hexaploid parent, CPI133872 (Zwart et al 2005). The 6DS QTL contributed by CPI133872 explained 24% of the variation in resistance, which is similar to the value reported here.…”

“…The 6DS QTL contributed by CPI133872 explained 24% of the variation in resistance, which is similar to the value reported here. QTLs on chromosome 2B for resistance to P. thornei have been detected in other mapping populations (Schmidt et al 2005;Zwart et al 2005). However, due to a lack of common markers on the 2BS region, comparisons between the location of the QTL identified in this study and other P. thornei resistance QTL studies could not be made.…”

“…These mapping studies were conducted using framework maps with a minimum number of marker loci used to detect marker-trait associations. The numbers of marker loci and genome coverage of these maps were 114 markers over 1987 cM for AUS1312 × Janz, 148 markers over 3230 cM for AUS4926 × Janz (Schmidt et al 2005), and 169 markers over 2570 cM for CPI133872 × Janz (Zwart et al 2005).…”

“…Recent molecular marker studies have identified putative quantitative trait loci (QTLs) for resistance to P. thornei on chromosomes 2B (Schmidt et al 2005;Zwart et al 2005), 3B (Schmidt et al 2005), and 6A and 6D (Zwart et al 2005), and a QTL for susceptibility to P. thornei on 1B (Schmidt et al 2005). These mapping studies were conducted using framework maps with a minimum number of marker loci used to detect marker-trait associations.…”

Evaluation of Turkish wild Emmers (Triticum dicoccoides Koern.) and wheat varieties cultivars for resistance to the root lesion nematodes (Pratylenchus thornei and Pratylenchus neglectus)

“…There have been many studies to identify new sources of resistance to RLN on Middle Eastern wheat varieties and landraces (Nicol et al, 2005;Schimdt et al, 2005;Zwart et al, 2005;Thompson, 2008;Thompson & Seymour 2011;Toktay et al, 2012a). One of the particular relevance to Australian wheat improvement programs were the P. thornei resistant accessions identified among Iranian landraces (Sheedy & Thompson, 2009) and wild relatives of wheat including T. dicoccoides (Sheedy et al, 2012).…”