Determining the genetic characteristics of Didymella arachidicola and its peanut host

Determining the genetic characteristics of Didymella arachidicola and its peanut host

Didymella arachidicola is the necrotrophic causative agent of net blotch in peanuts (Arachis hypogaea L.). It reduces yields and quality in Australia and many cooler production regions globally. Host resistance is generally thought of as the most effective form of control, however little has been studied of the pathogen itself and the genetic sources of host resistance. To effectively breed for durable resistance in a commercially viable peanut cultivar, it is necessary to understand the genetic diversity of D. arachidicola. This was achieved through hierarchically sampling a single peanut field in Queensland, Australia and investigating the genetic diversity through Diversity Array Technology, and the population structure of 84 isolates. The population structure of D. arachidicola indicated that the population consisted of one group with a high level of genetic diversity, containing 57 multi locus genotypes. This indicated that a single isolate of D. arachidicola was suitable to represent the diversity contained within a field. In addition, this study utilised whole genome sequences of two D. arachidicola strains to confirm homothallism. Nineteen peanut lines were evaluated under field and glasshouse conditions (winter and summer) to determine if phenotyping in the glasshouse related to the field disease response. A high level of correlation was demonstrated between nine-week-old plants in both glasshouse experiments and phenotyping in the field. To further understand host resistance, a total of 406 recombinant inbred lines segregating for net blotch resistance were phenotyped in the field and glasshouse and genotyped on a high-density SNP chip. Combining the phenotypic and genotypic data identified a total of 55 correlated quantitative trait loci (QTL). One QTL, qtlNB02A.3, explained 17.03% of the phenotypic variation. This will benefit peanut breeding programs enabling them to select for net blotch resistance using molecular tools. Once a net blotch resistant peanut genotype is developed there is a high chance that the resistance will be durable, as within the host there are several minor effect genomic regions involved in minimising the disease and there are minimal genetic populations within the pathogen.

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