Principal Investigator: Celeste Welty, O.S.U. Department of Entomology

Bob Precheur, O.S.U. Dept. of Horticulture & Crop Science
Mac Riedel, O.S.U. Department of Plant Pathology

Other Key Personnel:
Brad Bergefurd, Ag.-Enterprise Center, Hillsboro
Mark Schmittgen, Lane Avenue Horticulture Farm

Background and Objectives of Research:

Mosaic virus diseases vectored by aphids have caused up to 50% yield reduction in some Ohio pumpkin fields during the past few years. Our objective was to determine which viruses are infecting Ohio pumpkins, and to evaluate the efficacy of cultural and chemical practices for suppressing virus diseases.

Virus Survey: Results of third year of survey for viruses that infect pumpkins in Ohio:

Incidence of virus in pumpkin leaves from 26 Ohio fields, August-September 1996, as detected by ELISA tests.

Pumpkin leaves from 26 farms across Ohio were collected in August to September 1996 and frozen. Virus symptoms were common by mid- to late July, a bit earlier than the previous two years. At the University Lane Ave. farm in Franklin county, where leaves were sampled periodically in 1996, one field showed WMV was in 1% of samples on 15 July, and in 99% of samples on 5 August. than in 1994. See below. In another field, WMV was in 3% of samples on 5 August, 38% of samples on 12 August, and in 100% of samples on 22 August.

Frozen leaf samples were later ground and tested by enzyme-linked immunosorbent assay (ELISA) methods for the presence of five specific viruses that are most likely to infect cucurbits. We also tested for the poty (potato-y group of viruses in order to detect infectionby other less common viruses. Watermelon mosaic, papaya ringspot, and zucchini yellows are among the dozens of viruses in the poty group.

Summary

The most common virus in 1996 was watermelon mosaic virus (WMV), just as it was in 1994 and 1995. There were also farms where samples were positive for squash mosaic virus (SqMV). Unlike the previous year, there were no farms positive for cucumber mosaicvirus (CMV), papaya ringspot virus (PRsV), or zucchini yellow mosaic virus (ZYMV) in 1996. The poty tests in 1996 were positive where WMV tests were positive in most cases; results indicated that there was no need to test for additional viruses.

Results of the 3 Year Virus Survey of Ohio Pumpkins.

Results were fairly consistent rom year to year. Watermelon ,osaic virus has been the predominant virus found during the past 3 years, and it usually appears in early August. This virus seems to be characterized by severe mosaic symptoms on leaves (twisting, puckering, mottled colors) but fairly mild symptoms on fruit (lumps, bumps, uneven color). We have found that at least 48 species of aphids land in Ohio pumpkin fields and we have suspicions about which species might be vectoring the virus. This summer, we will attempt to test individual species to see which ones are capable of vectoring WMV.

a WMV = watermelon mosaic virus (formerly called WMV-2);

CMV = cucumber mosaic virus;

SMV = squash mosaic virus;

PRV = papaya ringspot virus (formerly called WMV-1).