New American Summer Squash Cultivars Possessing a High Level of Resistance to a Strain of Zucchini Yellow Mosaic Virus from China

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Cucurbit Genetics Cooperative Report 20:57-58 (article 25) 1997

R. Provvidenti
Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva, N.Y. 14456

Different strains of zucchini yellow mosaic virus (ZYMV) have been reported to infect cucurbits in many countries of the world (3,8). Two American strains of this virus are well known, he Florida (ZYMV-FL) and the Connecticut (ZYMV-CT) (6). The first is the most common and causes initially a “light green mosaic,” whereas the second incites the typical “yellow mosaic.” Both strains also cause a deep foliar serration, blisters, deformations, and plant stunting. There are a few other American strains which appear to be confined to some areas of the country. One from California incites symptoms closely resembling those caused by watermelon mosaic virus (unpublished). However, shape, size, and color of fruits produced by plants infected with the American strains of ZYMV are severely affected, rendering them unmarketable.

Following the assessment of the economic importance of this virus, efforts were made to find sources of resistance in squashes and other cucurbits. All cultivars of Cucurbita pepo, C. maxima and C. moschata were found to be susceptible, but an intense screening located high levels of resistance in Cucurbita ecuadorensis (Equador) and in a landrace of C. moschata ‘Nigerian Local’ (Nigeria) (6). Their resistance is very effective in controlling strains of ZYMV from Africa, the Americas, Asia, Europe, and Oceania. These two Cucurbita species also were demonstrated to be resistant to strains of cucumber mosaic virus (CMV), the two types of papaya ringspot virus (PRSV-p and PRSV-W), and watermelon mosaic virus (WMV). The ‘Nigerian Local’, however, is susceptible to squash mosaic virus (SqMV), whereas C. ecuadorensis offers a low level of tolerance to this virus (5).

Except in a few cases (2,7), attempts to transfer the ZYMV resistance from C. ecuadorensis into cultivated species were unsuccessful. More promising results were obtained with the resistance located in ‘Nigerian Local’. Thus, in recent years, a limited number of summer squash cultivars have been released by a few American seed companies. The Harris Moran Seed Company is the vendor of three zucchini-type cultivars possessing a high level of tolerance to ZYMV-FL: Tigress, Jaguar and Puma (1). Rogers Seed Company has recently released two new cultivars, Dividend and Revenue (9), which are also highly tolerant to ZYMV-FL. Since this strain is the most widespread in the USA, including Hawaii, it was used during the breeding of these five cultivars. Infected plants reacted to the Florida strain with normal growth, but leaves developed mild and sparse chlorotic spots. All fruits were of normal size, shape, and color. Hence, this tolerance has great economic importance in controlling the devastating effects of ZYMV-FL.

Studies had indicated that the resistances to ZYMV-FL in ‘Nigerian Local’ is rather complex, possibly involving one major factor plus some modifiers (4). However, when plants of ‘Dividend’, ‘Jaguar’, ‘Puma’, ‘Revenue’, and ‘Tigress’ were inoculated with a strain of ZYMV from China (ZYMV-CH), they displayed the same high level of resistance possessed by the original resistant parent, ‘Nigerian Local’. In September 1991, ZYMV-CH was found to severely infect the Cucurbitaceae growing near the capital, Beijing. In green house and filed tests, with susceptible hosts, this strain incited the characteristic ‘yellow mosaic’ that is caused by most strains of the virus (3).

The high level of resistance possessed by the new five American cultivars to the ZYMV-CH was unexpected, since it never was used in their breeding. Consequently, the development of valuable cultivars such as ‘Dividend’, ‘Jaguar’, ‘Puma’, ‘Revenue’ and ‘Tigress’ can be considered a significant accomplishment. They are very productive cultivars representing a significant step forward in the development of other commercial cultivars resistant to the major cucurbit viruses.

Literature Cited

  1. Harris Moran Seed company. 1995-97 Seed Catalogs.
  2. Herrington, M.E., R.S. Greber, P.J. Brown, and D.M. Persley. 1988. Inheritance of resistance to zucchini yellow mosaic virus in Cucurbita maxima cv. Queensland Blue x C. ecuadorensis. Queensland J. Agr. and Anim. Sci. 45:145-149.
  3. Lisa, V., and H. Lecoq. 1984. Zucchini yellow mosaic virus. No. 282. CMI/AAB Descriptions of Plant Viruses. Ferry Lane, Kew, Surrey, England p.4.
  4. Munger, H.M., and R. Provvidenti. 1987. Inheritance of resistance to zucchini yellow mosaic virus in Cucurbita moschata. Cucurbit Genet. Coop. 10:80-81.
  5. Provvidenti, R. 1993. Resistance to viral diseases of cucurbits. In: M.M. Kyle, ed. ‘Resistance to Viral Diseases of Vegetables’. Timber Press, Portland, OR pp. 8-43.
  6. Provvidenti, R., D. Gonsalves, and H.S. Humayadan. 1984. Occurrence of zucchini yellow mosaic virus in cucurbits from Connecticut, New York, FL and CA. Plant Dis. 68:443-446.
  7. Robinson, R.W. and D. Decker-Walters. 1997. Cucurbits. CAB international, Wallingford, Oxon, England (240 pp).
  8. Robinson, R.W., Rossario Provvidenti, and Joseph W. Shail. 1993. Tests for seedborne transmission of zucchini yellow mosaic virus. HortSci. 28:694-696.
  9. Rogers Seed Company – 1997 Catalog.