Molecular Breeding for Ascochyta Blight Resistance in Lentil: Current Progress and Future Directions

Abstract

Lentil (Lens culinaris Medik.) is a diploid (2n = 2x = 14), self-pollinating, cool-season, grain legume that is cultivated worldwide and is highly valuable due to its high protein content. However, lentil production is constrained by many factors including biotic stresses, majority of which are fungal diseases such as ascochyta blight (AB), fusarium wilt, rust, stemphylium blight, anthracnose, and botrytis gray mold. Among various diseases, AB is a major -problem in many lentil-producing countries and can significantly reduce crop production. Breeding for AB resistance has been a priority for breeding programs across the globe and consequently, a number of resistance sources have been identified and extensively exploited. In order to increase the efficiency of combining genes from different genetic backgrounds, molecular genetic tools can be integrated with conventional breeding methods. A range of genetic linkage maps have been generated based on DNA-based markers, and quantitative trait loci (QTLs) for AB resistance have been identified. Molecular markers linked to these QTLs may potentially be used for efficient pyramiding of the AB disease resistance genes. Significant genomic resources have been established to identify and characterize resistance genes, including an integrated genetic map, expressed sequence tag libraries, gene based markers, and draft genome sequences. These resources are already being utilized for lentil crop improvement, to more effectively select for disease resistance, as a case study of the Australian breeding program will show. The combination of genomic resources, effective molecular genetic tools and high resolution phenotyping tools will improve the efficiency of selection for ascochyta blight resistance and accelerate varietal development of global lentil breeding programs.

Construction of a high-density interspecific (Lens culinaris x L. odemensis) genetic map based on functional markers for mapping morphological and agronomical traits, and QTLs affecting resistance to Ascochyta in lentil

“…Several genetic linkage maps have previously been used to identify QTLs for Ascochyta blight resistance in lentil (reviewed by Rodda et al [89]), with magnitudes varying from 3% to 89% of the phenotypic variance evidenced. Common QTL locations between different studies are difficult to establish because of the differing nomenclature for linkage groups and the lack of common marker loci between the genetic maps.…”

“…Common QTL locations between different studies are difficult to establish because of the differing nomenclature for linkage groups and the lack of common marker loci between the genetic maps. In spite of that, the QTL named AB_NF1 on LG6 in the study of Sudheesh et al [67] is comparable in position to QTL5 on LG1 of Rubeena et al [85] and QTL1 on LG1 of Gupta et al [49], based on a common SSR locus location [89]. The AB_NF1 QTL accounted for 7% of the phenotypic variation in an F 6 RIL population from a cross of Indianhead x Northfield, being Northfield (ILL5588) a common parent in the majority of the studies published.…”

Characterization of Genetic and Allelic Diversity Amongst Cultivated and Wild Lentil Accessions for Germplasm Enhancement

“…For example, both Indianhead and Northfield (syn. ILL5588, Nei's coefficient value 0.69194), known to be resistant to Ascochyta Blight (Rodda et al, 2017), have been crossed to each other to produce improved levels of disease resistance in the breeding germplasm (Rodda et al, 2017). The information generated in the current study provides a database for breeders to select Lens accessions for future crossing strategies in order to introgress novel alleles.…”

Widening the genetic base of cultivated gene pool following introgression from wild Lens taxa

“…Using RIL populations, QTLs for stemphylium blight and rust resistance (Saha, Sarker, Chen, Vandemark, & Muehlbauer, 2010a, 2010b) and seedling and pod stage ascochyta blight resistance (each of three QTLs, accounted for 34% and 61% of the total estimated phenotypic variation (Gupta, Taylor, et al, 2012) were identified. Nevertheless, identified flanking markers have potential to be used in MAS especially for disease-resistance genes with single gene inheritance or codominance (Chowdhury, Andrahennadi, Slinkard, & Vandenberg, 2001;Eujayl et al, 1998;Ford, Pang, & Taylor, 1999;Kaur et al, 2014;Rodda et al, 2017;Rubena, Taylor, Ades, & Ford, 2006;Tullu et al, 2003). However, validation of these linked markers would remain important challenge for the success of adoption of such markers in lentil improvement programme.…”

“…These AB-resistant markers were evaluated on a diverse lentil panel, which had nearly 86% accuracy for phenotypic response to be potentially adopted in lentil breeding programmes. Ascochyta blight-resistant genes have been identified through lentil genomics and integrated genetic linkage map, EST libraries and draft genome sequences have been generated (Rodda et al, 2017). Among few attempts to dissect genes of interest from wild genotypes using mapping and QTL analysis, a linkage map of 94 RILs from a cross between two L. ervoides genotypes has been developed (Bhadauria, Ramsay, Bett, & Banniza, 2017 34 countries with a wide range of variation for zinc (Zn) and iron (Fe) concentration in seeds were used, and two SNP markers tightly linked to Fe and one linked to Zn concentration were identified using marker-trait association analysis (Khazaei et al, 2017).…”