NOTES ON THE CHANGE OF THE CAUSAL SPECIES OF CUCURBIT POWDERY MILDEW IN THE U.S.

Authors: McCreight, James - Jim

Submitted to: Cucurbit Genetics Cooperative Report
Publication Type: Research Notes
Publication Acceptance Date: 5/27/2004
Publication Date: 1/20/2007
Citation: Mccreight, J.D. 2007. Notes on the change of the causal species of cucurbit powdery mildew in the U.S. Cucurbit Genetics Cooperative Report. 27:8-23.

Interpretive Summary: Powdery mildew is an important disease of many crop species worldwide. On melon, early infection can kill the plants while late infection can reduce fruit quality through reduced sugar concentration. Effective disease control begins with the accurate identification of the causal organism. Beginning with the first report of powdery mildew on melon in Imperial Valley in 1925 through 1967, the causal organism of powdery mildew on melon and other cucurbit species in the U.S. was generally regarded as Erisyphe cichoracearum. In 1968, Sphaerotheca fuliginea was first cited as the cause of powdery mildew on cantaloupe in the U.S. Since that time, only Sphaerotheca fuliginea has been reported in commercial production fields of melons and other cucurbits in the U.S. This paper documents the technical background supporting the seemingly abrupt identity of the cucurbit powdery mildew pathogen through examination of the scientific literature and correspondence between G.W. Bohn, B. Ballantyne and D.M. McLean.

Technical Abstract: Beginning with the first report of powdery mildew (PM) on melon in Imperial Valley in 1925 through 1967, the causal organism of PM on melon and other cucurbit species in the U.S. was generally regarded as Erisyphe cichoracearum (Ec). In 1968, while Sf was named as the cause of PM without mention of Ec in a semi-popular article on control of PM on cucumber and squash, two reports on genetic resistance to PM referred only to Ec. Since that time, only Sf has been reported in commercial production fields of melons and other cucurbits in the U.S. although isolates of Ec capable of infecting cucurbits have been documented form non-agricultural sources. The change in the identity of the dominant PM pathogen was documented in the scientific literature in Asia, Europe, India and Australia, but not the U.S. This paper documents the technical background supporting the seemingly abrupt identity of the cucurbit powdery mildew pathogen in the U.S. through examination of the scientific literature and correspondence between G.W. Bohn in California, B. Ballantyne in Australia and D.M. McLean in South Carolina.