Cucurbit Genetics Cooperative Report 7:58-59 (article
The Importance of Monitoring Races of Powdery Mildew on Muskmelon
Thomas, C.E., A.N. Kishaba, J.D. McCreight, and P.E. Nugent
USDA/ARS, U.S. Vegetable Laboratory, Charleston, SC 29407 (first
and fourth authors), USDA/ARS, Boyden Entomological Laboratory,
Riverside, CA 92521 (second author); and USDA/ARS, U.S.
Agricultural Research Station, Salinas, CA 93915 (third author)
Powdery mildew is a widespread and often production limiting
disease of muskmelon (Cucumis melo L.). Resistance against
it is one object of many breeding programs. For many years the
incitant fungus was considered to be Erysiphe
cichoracearum DC ex Merat. All recent reports, however,
indicate Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll.
as the incitant. Sitterly (2) presents an excellent review of
this situation. Three races of the powdery mildew pathogen have
been demonstrated to occur in the U.S.A. (2, 4). The importance
of monitoring these races, especially to breeding programs, is
In 1980 the authors began a cooperative research effort to
determine which races of powdery mildew occurred on muskmelon in
different geographic areas of the U.S.A. The differential
cultivars listed by Thomas (4) and other cultivars with known
reactions to individual races have been evaluated repeatedly for
their reaction to powdery mildew in both the greenhouse and field
at Brawley, Salinas, and Riverside, California; Charleston, South
Carolina; and Weslaco, Texas.
Thus far we have confirmed a shift in the natural population of
powdery mildew at Brawley, California, from a predominance of
race 2 in 1982 to race 1 in 1983 and several shifts back and
forth from race 3 to race 1 at Weslaco, Texas from 1980 through
1982. In 1983 we detected a shift in our greenhouse culture of
powdery mildew at Charleston, South Carolina from race 3 to race
1. This shift occurred within a period of a few weeks and would
have gone undetected for some time had we not maintained
differential cultivars in the greenhouse.
Due to the population shifts that we and Sowell (3) have detected
and the rapidity with which these shifts can occur, we recommend
that races of the powdery mildew pathogen on muskmelon be
monitored in research efforts, especially breeding programs.
Table 1 lists the minimum recommended cultivars and their
reactions to races 1, 2, and 3 of powdery mildew to accomplish
this monitoring. The senior author will furnish small quantities
of seed of these cultivars to interested researchers who are
willing to share with us the reactions of these cultivars in
Table 1. Reactions of cantaloup cultivars to races of powdery
mildew incited by Sphaerotheca fuliginea.
Hale's Best Jumbo
- Jagger, I.C., T.W. Whitaker and D.R. Porter. 1938. A new
biologic form of powdery mildew on muskmelons in the Imperial
Valley of California. Plant Dis. Reptr. 22:275-276.
- Sitterly, W.R. 1978. Powdery mildews of cucurbits. In: The
Powdery Mildews. D. M. Spencer (ed.), Academic Press, New York.
- Sowell, G., Jr. 1982. Population shift of Sphaerotheca fuliginea on muskmelon from race 2 to race 1 in the southeastern United
States. Plant Dis. Reptr. 66:130-131.
- Thomas, C.E. 1978. A new biological race of powdery mildew of
cantaloups. Plant Dis. Reptr. 62:223.