Submitted to: Crucifer Genetics Workshop
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2006
Publication Date: September 30, 2006
Citation: Wechter, W.P., Keinath, A.P., Smith, J.P., Farnham, M.W. 2006. A Search for Peppery Leaf Spot Resistance in Brassica Juncea Germplasm. Proceedings of the 15th Crucifer Genetics Workshop: Brassica 2006. 30 Sep-4 Oct 2006. Wageningen, The Netherlands. p 126. Technical Abstract: The southeastern United States leads the country in the production of leafy crucifer greens, including turnip greens (Brassica rapa L.), mustard greens (B. Juncea L.), collard (B. oleracea L.) and kale (B. oleracea). Production of these vegetables is continuous throughout the four seasons in this region with crops coming out of the field every month of the year at some specific locations. Bacterial leaf spot (also called peppery leaf spot) caused by the bacterium Pseudomonas syringae pathovar maculicola has emerged as a serious disease problem on leafy greens in the Southeast. Severe damage and losses due to it have been reported by some of the largest vegetable growers in South Carolina. Based on experience of these growers, it appears that available commercial cultivars of greens are susceptible to peppery leaf spot. The objective of this study was to evaluate a subset of the United States Plant Introduction collection of B. juncea to identify germplasm exhibiting resistance to this bacterial disease. Two hundred accessions designated oilseed B. juncea and 51 designated vegetable B. juncea were evaluated. Plants of each accession at the three-to-four-leaf stage were artificially inoculated with a water-based inoculum containing 10 million CFU ml-1 and incubated overnight for 16 h in a humid chamber in a greenhouse. Plants were then placed on a greenhouse bench for one week, after which they were scored for infection and compared to an inoculated susceptible check. Accessions exhibited varied responses to inoculation with P. syringae pv. maculicola ranging from very susceptible to highly resistant. Accessions rated most resistant were retested to confirm the resistant phenotypes. In total, three oilseed types exhibited high levels of resistance with one (of Ethiopian origin) appearing to be nearly immune. Only one vegetable B. juncea accession (of Chinese origin) was highly resistance. Resistant accessions will be studied further to determine the nature of resistance and the feasibility of transferring it to improved cultivars.