Abstract
Selection for resistance against gray leaf spot (GLS) is a major objective in the lupin breeding programs. A segregation ratio of 1:1 (resistant:susceptible) in F8 recombinant inbred lines (RIL8) derived from a cross between a breeding line 83A:476 (resistant to GLS) and a wild accession P27255 (susceptible to GLS) indicated that GLS was controlled by a single major gene. To develop molecular markers linked to GLS, in the beginning, only 11 resistant lines and six susceptible lines from the 83A:476 and P27255 population were genotyped with MFLP markers, and three MFLP markers were identified to be co-segregated with GLS. This method was very efficient, but the markers were located outside of the gene, and could not be used in other germplasms. Then QTL analysis and fine mapping were conducted to identify the gene. Finally, the gene was narrowed down to a 241-kb region containing two disease resistance genes. To further identify the candidate gene, DNA variants between accessions Tanjil (resistant to GLS) and Unicrop (susceptible to GLS) were analyzed. The results indicated that only one SNP was detected in the 241 kb region. This SNP was located in the TMV resistance protein N-like gene region and also identified between 83A:476 and P27255. Genotyping the Tanjil/Unicrop RIL8 population showed that this SNP co-segregated with GLS resistance. The phylogenetic tree analysis of this gene among 18 lupin accessions indicates that Australian resistant breeding line/varieties were clustered into one group and carry two resistant alleles, while susceptible accessions were clustered into different groups.
Highlights
Molecular markers linked to genes of agronomic traits can be applied in plant breeding to hasten genetic improvement
For the gray leaf spot disease phenotypes, all the plants of parental line 83A:476 were resistant to Gray leaf spot (GLS), while all the plants of P27255 were susceptible
We wanted to develop molecular markers linked to GLS and use immediately in breeding programs, so an efficient method was adopted to identify the locus
Summary
Molecular markers linked to genes of agronomic traits can be applied in plant breeding to hasten genetic improvement. For agronomic traits without the knowledge of gene sequences, one of the methodologies for developing widely applicable molecular markers is to design several markers linked to the target genes, followed by a validation step to test the candidate markers and select the best one for MAS (Yang et al, 2008). Using this concept, diagnostic markers have been developed and applied for anthracnose disease resistance (You et al, 2005) and phomopsis stem blight disease resistance (Yang et al, 2013a) selection in Australian national lupin breeding programs. The whole-genome sequencing approach offers tremendous potential for developing diagnostic markers and/or identifying genes in plant breeding
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