Identification of Genetic Loci Underlying Anthracnose Fruit Rot Resistance In Blueberry

Abstract

Anthracnose fruit rot (AFR), caused by Colletotrichum fioriniae, is a significant challenge for blueberry production in Florida. This study aimed to establish a robust screening protocol for evaluating AFR resistance in blueberry genotypes and identify genetic loci associated with resistance. Two inoculation methods, punctured (mechanically wounded) and non-punctured (intact), were tested over varying incubation periods (7-day and 14-day). The punctured 7-day method emerged as the most reliable for generating consistent and distinguishable disease phenotypes, allowing efficient screening during the short fruiting window of southern highbush blueberries. A phenotypic analysis of a segregating population revealed a wide variation in AFR susceptibility, with ~6.4% of genotypes showing high resistance and ~23% exhibiting high susceptibility. Disease expression ratings allowed for categorization into five distinct susceptibility groups. The phenotypic data were integrated with genotypic information through genome-wide association studies (GWAS). This identified two loci on chromosome 8 significantly associated with AFR response explained about 17% of disease resistance variation, one locus exhibited an additive effect linked to a DUF761 domain protein, and another showing a simplex dominant effect associated with a Ring_Ubox protein. Both proteins are implicated in stress and defense responses, as evidenced by studies in model plants like Arabidopsis thaliana. Hierarchical clustering of genetic data revealed no clear grouping of resistant or susceptible genotypes, indicating a complex inheritance pattern of AFR resistance. The identified loci provide insight into the polygenic nature of AFR resistance and present opportunities for developing molecular markers to enhance selection efficiency in breeding programs. This study successfully validated a screening protocol and identified genetic regions linked to AFR resistance, laying the groundwork for breeding AFR-resistant southern highbush blueberry cultivars. The findings emphasize the need for focused breeding efforts to introgress resistance traits and highlight the potential of marker-assisted selection for accelerating the development of disease-resistant blueberries.