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United States Department of Agriculture

Agricultural Research Service

Title: Identification of Resistance to Peppery Leaf Spot among Brassica Juncea and Brassica Rapa Plant Introductions

Authors
item Wechter, William
item Farnham, Mark
item Smith, J - CLEMSON UNIVERSITY
item Keinath, A - CLEMSON UNIVERSITY

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2007
Publication Date: July 16, 2007
Citation: Wechter, W.P., Farnham, M.W., Smith, J.P., Keinath, A.P. 2007. Identification of Resistance to Peppery Leaf Spot among Brassica Juncea and Brassica Rapa Plant Introductions. HortScience. 42:1140-1143.

Interpretive Summary: Brassica leafy greens (Brassica juncea L. and B. rapa L.) represent one of the most economically important vegetable crop groups in the southeastern United States. In the last 10 years, numerous occurrences of a leaf spot disease on these leafy vegetables have been reported in several states. This disease, known as peppery leaf spot, is now causing serious crop losses. To date, it appears that all cultivars of the Brassica leafy greens are susceptible and available pesticides for control of this disease appear unable to reduce the disease to acceptable levels. We screened 672 U.S. Plant Introductions of B. juncea and B. rapa for resistance to this disease in greenhouse assays. Only two accessions, both B. juncea (‘PI 195553’ and ‘G 30988’), were found to have acceptable levels of resistance to peppery leaf spot. Both of these accessions are potentially useful as parental lines in breeding programs to develop Brassica cultivars resistant to peppery leaf spot.

Technical Abstract: Brassica leafy greens (Brassica juncea L. and B. rapa L.) represent one of the most economically important vegetable crop groups in the southeastern United States. In the last 10 years, numerous occurrences of a leaf spot disease on these leafy vegetables have been reported in several states. This disease, known as peppery leaf spot, is now causing serious crop losses and has been attributed to the bacterial phytopathogen Pseudomonas syringae pv. maculicola (Psm). To date, it appears that all cultivars of the Brassica leafy greens are susceptible and available pesticides for control of this disease appear unable to reduce the disease to acceptable levels. Thus, we undertook a search for potential resistance to this disease among accessions of B. juncea and B. rapa included in the United States Plant Introduction (PI) collection. In greenhouse trials we screened commercial cultivars and 672 U.S. Plant Introductions (226 B. juncea and 446 B. rapa) for resistance to Psm with artificial inoculation. Although severity of disease symptoms were significantly different among inoculated accessions, no acceptable levels of resistance were found in any of the more than 400 B. rapa accessions tested. Only two B juncea accessions (‘PI 195553’ and ‘G 30988’) of 226 tested had acceptable levels of resistance that might prove economically useful.

Last Modified: 7/23/2014