Abstract
Bacterial leaf spot (BLS), caused by Pseudomonas syringae pathovar aptata (Psa), is an emerging seedborne, foliar disease affecting both table beet and Swiss chard. There is no known resistance to BLS in beet or chard. The University of Wisconsin-Madison table beet breeding program has been screening for resistance in the Beta vulgaris crop complex. A diversity panel, modified from the Wisconsin Beta Diversity Panel (WBDP) and comprised of 219 accessions from the Beta vulgaris crop complex, including sugar beet and fodder beet, was assembled and genotyped for SNP data. These accessions were screened by foliar inoculation of Psa and visually evaluated for percentage of diseased leaf tissue. Overall, sugar beet and Beta maritima accessions had the lowest BLS response (indicating high potential for sources of resistance), whereas table beet accessions had the largest range of responses, with several matching the resistance levels of sugar beet. Phenotypic means were adjusted using best linear unbiased estimates, and two different software programs, GWASpoly and GAPIT3, were utilized to conduct a genome wide association study (GWAS). An association with BLS response was detected on chromosome one in the full WBDP, explaining upwards of 21% of the variation in the phenotype. Eleven candidate genes, described and annotated in sugar beet, were associated with this QTL. Marker Chr1_61344476 may be useful in breeding for BLS resistance in members of the Beta vulgaris crop complex.