Genetics of Resistance to Ascochyta Blight in Lentil
The aim of this study was to gain insight into the nature of resistance genes and mechanisms of resistance present in different ascochyta blight (AB) resistant genotypes of lentil to efficiently select non-allelic AB resistance genes mediating different mechanisms of resistance for gene pyramiding. Recombinant inbred lines (RILs) from all possible crosses among AB resistant Lens culinaris genotypes CDC Robin, 964a-46, ILL 7537 and ILL 1704 were subjected to allelism tests. Efforts were also made to understand the genetics of resistance in the L. ervoides accession L-01-827A. LR-18, a RIL population from the cross CDC Robin × 964a-46 was subjected to quantitative trait loci (QTL) mapping using a comprehensive genetic linkage map previously developed from polymorphic SNPs, SSRs and phenotypic markers. Results of allelism tests suggested that genes conditioning resistance to ascochyta blight in all lentil genotypes were non-allelic. Two complementary recessive resistance genes in L-01-827A were detected. QTL analysis indicated that CDC Robin and 964a-46 were different at two AB resistance QTLs. Histological tests suggested that cell death inhibition in CDC Robin, and reduced colonization of epidermal cells in 964a-46 might be the mechanisms of resistance in these genotypes. Comparing the expression of key genes in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways of CDC Robin and 964a-46 suggested that the SA pathway was strongly triggered in 964a-46. However, the JA pathway was triggered in both, but at a lower expression level in 964a-46 than in CDC Robin. RNA-seq analysis revealed a number of candidate defense genes differentially expressed among genotypes with hypothetical actions in different layers of the plant defense machinery. The expression levels of the six candidate defense genes measured by quantitative real-time PCR analysis was correlated with those of RNA-seq. In conclusion, 964a-46 and CDC Robin mediated resistance to ascochyta blight through different resistant mechanisms, making them ideal candidates for resistance gene pyramiding. Gene pyramiding can be accelerated using closely linked markers to CDC Robin and 964a-46 resistance genes identified through QTL analysis.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorVandenberg, Albert; Banniza, Sabine
CommitteeBett, Kirstin; Beattie, Aaron; Bonham-Smith, Peta; Bai, Yuguang
Copyright DateOctober 2014
Ascochyta lentis, L. culinaris, L. ervoides, allelism test, QTL analysis, Salicylic acid, Jasmonic acid, microscopy, RNA-seq analysis