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Title: Myrothecium roridum leaf spot and stem canker on watermelon in the southern Great Plains: Possible factors for its outbreak

Author
item Bruton, Benny
item Fish, Wayne

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2011
Publication Date: 1/30/2012
Citation: Bruton, B.D., Fish, W.W. 2012. Myrothecium roridum leaf spot and stem canker on watermelon in the southern Great Plains: Possible factors for its outbreak. Plant Health Progress. Available: doi:10.1094/PHP-2012-0130-01-BR.

Interpretive Summary: Diseases are generally the greatest yield-limiting factor for watermelon across the U.S. In 2010, a foliar and stem-lesion disease was observed for the first time in Oklahoma causing moderate to severe defoliation of watermelon plants. The outbreak occurred on 20 different watermelon cultivars in an experimental field and was demonstrated to be the result of a rare, widespread infection by the fungus, Myrothecium roridum. This was only the second reported incidence in the U.S. of M. roridum pathogenesis on watermelon under field conditions. Symptoms were illustrated and described in detail for easier visual identification of the disease by breeders, growers, extension personnel, and researchers.

Technical Abstract: Diseases are generally the greatest yield-limiting factor for watermelon across the U.S. In 2010, a foliar and stem-lesion disease was observed for the first time in Oklahoma causing moderate to severe defoliation. Using microscopic examination, the physical features of the fungus were consistent with Myrothecium roridum. Because of continual cantaloupe (very susceptible) production in the field for 7 of the last 10 years, inoculum was likely high. High natural inoculum, coupled with warm and wet conditions during a four-week period leading up to the disease outbreak, created ideal conditions for this disease to flourish. There was a wide range of susceptibility among watermelon cultivars in the field indicating a moderately high level of resistance to Myrothecium leaf spot in some watermelon cultivars. Symptoms were illustrated and described in detail for easier visual identification of the disease by breeders, growers, extension personnel, and researchers.