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Identification and Characterization of Russet on Snap Beans Caused by
Plectosporium tabacinum
H. R. Dillard, A. C. Cobb, D. A. Shah, and K. E. Straight,
Department of Plant Pathology, Cornell University, NY State Agricultural Experiment Station
What was previously thought to be a relatively unimportant condition on snap bean pods became a significant problem for commercial bean growers in 2000 and 2004. The condition, which growers had seen on occasion in previous years, appeared on pods as diffuse, superficial, light brown necrotic areas or flecks with undefined borders. This problem, termed russet, appears to affect only the pods and no other plant parts. Snap bean russet led to a 100% loss in marketability of some fields in Maryland in 2000 and New York in 2000 and 2004. Russet appeared, in all cases reported, following a heavy rainfall a
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few days before harvest. The cause of snap bean pod russet remained unknown.
In this report, we demonstrate that russet on snap bean pods is caused by the fungus Plectosporium tabacinum. Pods must be wet for at least 48 hours to produce the type of symptoms seen in commercial fields. Large pods, close to harvest size, are more likely to develop russet than smaller pin pods. P. tabacinum is the same fungus that causes blight on cucurbits (squash, pumpkin, and zucchini). Unlike with snap bean russet, symptoms appear on several parts of these plants. It remains unclear whether the strain of P. tabacinum causing russet symptoms on snap beans is the same one responsible for blight on cucurbits.
APS copyright protected.
Reprinted with permission from Dillard, H. R., Cobb, A. C., Shah, D. A., and Straight, K. E. 2005. Identification and characterization of russet on snap beans caused by Plectosporium tabacinum. Plant Disease 89:700-704.
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