|Coffey, Michael - UNIV.CALIF.,RIVERSIDE|
|Turini, Thomas - UNIV.CALIF.,COOP.EXT.|
|Matheron, Michael - UNIV.ARIZONA COOP.EXT.|
Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: February 4, 2005
Publication Date: June 20, 2005
Citation: McCreight, J.D., Coffey, M.D., Turini, T.A., Matheron, M.E. 2005. Field evidence for a new race of powdery mildew on melon. Hortscience 40:888. Technical Abstract: Races 1 and 2 of Podosphaera xanthii (syn. Sphaerotheca fuliginea) were defined in Imperial Valley, Calif. 1938 when P. xanthii overcame genetic resistance in 'PMR 45'. Race 3 was first observed in the U.S. in 1976 in Texas; 15 additional races of P. xanthii have been reported in the literature since 1996. Races 1 and 2 have been common in Arizona and California based upon the effectiveness of the powdery mildew resistance genes in commercially available melon cultivars grown in these states. Field data from 11 commonly used melon P. xanthii race differentials in 2001 and 2002 indicated the presence of race 1 in the Imperial Valley and San Joaquin Valley of California, and Yuma, Arizona. In spring 2003, the powdery mildew race situation changed. The first evidence was the occurrence of a severe and widespread infection of powdery mildew in a commercial cantaloupe field. The 11 powdery mildew race differentials were susceptible to powdery mildew in a nearby replicated field test. PI 313970, a melon from India, was resistant to this apparent new race of powdery mildew.