Novel Sources of Resistance to Bacterial Leaf Blight in the USDA Brassica rapa Collection

Bacterial leaf blight, caused by Pseudomonas cannabina pv. alisalensis (Pcal), is a devastating disease that has spread worldwide over the past 20 years. Pcal can infect all Brassica crops and leads to yield losses of Brassica leafy greens across the southeastern United States every year. There are no commercial cultivars of turnip greens with resistance to Pcal and no effective bactericides available. We report the first identification of resistant sources in Brassica rapa L. against bacterial leaf blight caused by Pcal. The United States Department of Agriculture (USDA) accessions of B. rapa (275 accessions) were screened through multiple tests in greenhouse trials. The three commercial cultivars tested exhibited an intermediate response across all tests and retests. Three accessions (Ames 7572, PI 649171, and PI 649183) with significant resistance were identified in the B. rapa germplasm collection. The identified accessions are an important source for development of B. rapa cultivars resistant to Pcal and introgression of the resistant loci into B. napus cultivars.