Cucurbit Genetics Cooperative Report 10:81-82 (article 42) 1987

Lack of Seed Transmission in Squash and Melon Plants Infected with Zucchini Yellow Mosaic Virus.

R. Provvidenti and R. W. Robinson

Departments of Plant Pathology and Horticultural Sciences, New York State Agricultural Experiment Station, Cornell Univertsity, Geneva, NY 14456

The rapid spread of zucchini yellow mosaic virus (ZYMV) to cucurbits grown in different areas of the world strongly suggests its transmission through seed. Early attempts to demonstrate this important avenue of dissemination in squash and melon seeds were unsuccessful (2,3,4). More recently, Davis and Mizuki (1) reported that ZYMV was transmitted in seed of the Black Beauty cultivar of Cucurbita pepo. However, though the virus recovered from infected seeds appeared to be serologically related to ZYMV, it caused only a limited systemic infection and inconspicuous symptoms in 'Black Beauty' and 'Multipik' squash. Since this seedborne virus incited symptoms that were radically different from those usually attributed to ZYMV, their claim of seed transmission must be considered inconclusive.

In the last two years, we have attempted to demonstrate transmission of ZYMV in summer squash and melon seeds. In the summer of 1985, 4266 squash plants were grown from three seed lots of Cucurbita pepo deriving from ZYMV-infected plants that were kindly provided by F. Angell (A. L. Castle, Inc. Hollister, CA). None of these plants exhibited symptoms associated with ZYMV infection. In 1986, a second attempt utilized locally grown 'Ambassador' seeds harvested in 1985 from severely malformed ZYMV-infected fruits. Of 2475 plants, none exhibited symptoms caused by this virus. In the same year, a third attempt involved 'Iroquois' melon seeds, which were, harvested in 1985 from ZYMV infected plants. Although these seeds were small and malformed, germination was about 90%. None of the 100 plants from these seeds, that were grown in the greenhouse for about two months, was found infected by ZYMV. A field trial with 334 'Iroquois' plants deriving from the original seed lot was also free of ZYMV infection.

Except for the melon plants grown in the greenhouse, no assays were attempted to detect ZYMV infection. However, field grown plants were kept under constant observation until the end of the season, and none exhibited symptoms of ZYMV infection. The squash and melon plants eventually became infected with other viruses that are prevalent in the region, such as watermelon mosaic virus 2, cucumber mosaic virus, and clover yellow vein virus (= the severe strain of bean yellow mosaic virus).

Both here and abroad, circumstantial evidence has strongly suggested seed transmission of ZYMV in squash, melon, and watermelon. Though recent trials have been unsuccessful or inconclusive, more research is needed to clarify this very important point.

Literature Cited

1. Davis, R. F., and M. K. Mizuki. 1986. Seed transmission of zucchini yellow mosaic virus (ZYMV) in Cucurbita pepo. Proc. Workshop Epid. Plant Virus Dis. Part II:6-7
2. Lecoq, H., M. Pitrat, and M. Clement. 1981. Identification et caracterisation d'un potyvirus provoquant la maladie du rabougrissement jaune du melon. Agronomie 1:827-834.
3. Lisa, V., and H. Lecoq. 1984. Zucchini yellow mosaic virus. Description of Plant Viruses No. 282. C.M.I./A.A.B., Kew, Surrey, England.
4. Nameth, S. T., J. A. Dodds, and A. D. Paulus. 1985. Zucchini yellow mosaic virus associated with severe diseases of melon and watermelon in southern California desert valleys. Plant Dis. 69:785-788.