Genetic architecture of Cercospora leaf spot response in table beet with implications for other Beta vulgaris crop types

Table beet (Beta vulgaris subsp. vulgaris) production is threatened by the fungal disease Cercospora leaf spot (CLS). Infections are common across table beet's closest relatives, including Swiss chard, sugar beet, and fodder beet (all B. v. subsp. vulgaris). This study was conducted to characterize the genetic architecture underlying CLS response in table beet. A secondary objective was to test whether CLS-associated loci in table beet perform similarly across B. vulgaris crops. A diversity panel comprised of 168 table beet accessions and with an additional 70 accessions from all close relatives of table beet was screened for CLS response in replicated and inoculated field trials. Results from a genome-wide association study of additive effects revealed seven quantitative trait loci mapped to chromosomes 1, 3, 7, and 9 to explain 30% of the phenotypic variation for CLS response in table beet. When the performance of these loci was compared between a table beet background and a background of Swiss chard, sugar beet, and fodder beet, two loci exhibited significantly different responses. Among the B. vulgaris crops, these loci may be unique to table beet germplasm and could be useful for the improvement of CLS resistance in other crop types. For the improvement of CLS resistance in table beet, this study identified the cultivar Winter Keeper as a potentially valuable source of resistance. The architecture of CLS response points to recurrent selection and backcross methods as effective strategies for the improvement of CLS resistance in table beet.