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Research Project: Genetic Enhancement of Watermelon, Broccoli, and Leafy Brassicas for Economically Important Traits

Location: Vegetable Research

Title: Suppression of bacterial blight on mustard greens with host plant resistance and Acibenzolar-S-Methyl

Author
item Keinath, Anthony - Clemson University
item Wechter, William - Pat
item Farnham, Mark

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2016
Publication Date: 9/1/2016
Citation: Keinath, A.P., Wechter, W.P., Farnham, M.W. 2016. Suppression of bacterial blight on mustard greens with host plant resistance and Acibenzolar-S-Methyl. Plant Disease. 100:1921-1926.

Interpretive Summary: Several bacterial pathogens cause leaf spot or blight diseases on leafy green Brassica crops including mustard, turnip, and collard greens. A relatively new pathogen called Pseudomonas cannabina pv. alisalensis has been causing a particularly damaging blight of leafy greens that has now become a very significant problem in many greens producing areas of the U.S. The resulting economic losses attributable to the disease have been very significant for numerous producers in the Southeast. ARS scientists in Charleston, SC, in cooperation with a Clemson university colleague conducted field studies to determine if a chemical called Acibenzolar-S-methyl could be used in conjunction with a resistant variety to reduce the severity of blight disease on mustard greens. The results of these experiments showed that the most effective way to control the blight disease was to simply grow the resistant variety ‘Carolina Broadleaf’, which was developed by the ARS scientists. Acibenzolar-S-methyl actually damaged leaves in some cases and did not reduce disease severity as much as did use of the resistant variety. Results of these experiments will be conveyed to mustard greens growers in the southeastern U.S. who can increase profits by growing the resistant ‘Carolina Broadleaf” as a management practice to reduce crop losses due to the blight disease.

Technical Abstract: Bacterial blight, caused by Pseudomonas cannabina pv. alisalensis, attacks the leaves of most brassica vegetables, including mustard greens (Brassica juncea). ‘Carolina Broadleaf,’ a new mustard cultivar, is resistant to bacterial blight. Acibenzolar-S-methyl (trade name Actigard) has been used to manage other diseases caused by Pseudomonas on a variety of crops. The objective of this study was to evaluate host plant resistance, acibenzolar-S-methyl, and the combination to manage bacterial blight. Three field experiments were done in spring and fall 2011 and fall 2014. Acibenzolar-S-methyl was applied once before and once after plants were inoculated. Bacterial blight was 81% less on nontreated Carolina Broadleaf than on nontreated Florida Broadleaf (P = 0.0003). Acibenzolar-S-methyl applications reduced severity of bacterial blight by 55% compared to the water control treatment on the susceptible cultivar ‘Florida Broadleaf.’ However, acibenzolar-S-methyl significantly injured leaves of Carolina Broadleaf in two experiments and injured leaves of Florida Broadleaf in one experiment. Across all three experiments, acibenzolar-S-methyl reduced the mean weight of diseased leaves by 36% compared to water (P = 0.002). Mean weight of diseased leaves was 53% less with Carolina Broadleaf than with Florida Broadleaf (P < 0.0001). Consequently, the mean weight of symptomless leaves was 34% greater for Carolina Broadleaf than for Florida Broadleaf (P = 0.0014). Overall, host plant resistance was more effective than acibenzolar-S-methyl for managing bacterial blight on mustard greens.