Cucurbit Genetics Cooperative
Other Crop Genetics Cooperatives
Home About Membership Reports Gene Lists Conferences Links Search NCSU
Cucurbit Genetics Cooperative Report 4:42-43 (article 23) 1981

Do Cucurbita Plants with Silvery Leaves Escape Virus Infection? Origin and Characteristics of NJ260

O. Shifriss

Department of Horticulture and Forestry, Cook College, Rutgers University, New Brunswick, NJ 08903

NJ260 is a new B/B inbred of Cucurbita pepo L. This inbred was developed from a cross between 'Caserta', B+/B+, and 'Precocious Early Prolific', B/B (7), in an attempt to synthesize a predominantly female line (6). The leaves of 'Caserta' become moderately mottled sometime after the seedling stage. The leaves of 'Precocious Early Prolific' are non-mottled.

Under comparable field conditions in our area, NJ260 is an extra dwarf whose relatively small leaves are intensely mottled from the seedling stage and on, becoming uniformly silvery with the passage of time. It is a highly pistillate line bearing curved fruits with a constricted neck. It is also a low seed producer, perhaps due to poor pollen tube growth in a morphologically abnormal style. But the most extraordinary feature of NJ260 during the past five years has been its complete freedom from virus infection under field conditions in which non-silvery plants exhibit close to 100% infection at the end of the growing season.

The "mottled-leaf" character was described previously as "silver gray areas in axils of leaf veins", and genetic data, based on a limited number of crosses, demonstrated that this character is conditioned by a dominant gene, M, in maxima, moschata, and pepo (2, after 3 and 5). Scott and Riner (5) pointed out that the mottled effect "is visible only on the upper surface of the leaves and is a result of light-colored gray-green tissue being surrounded by the darker green tissue". Furthermore, results of their starch test have led them to state that "apparently the mottling is not due to chlorophyll deficiency in the light-colored tissues". Scarchuk and Lent (4) reported that the palisade cells in green areas are in close contact with the epidermis, as well as with each other. By contrast, the palisade cells in silvery areas are not in close contact with either the epidermis or with each other, thus resulting in air spaces. And "these air spaces are responsible for the silvery-gray color".

According to my observations, the expression of the silvery trait (silvery pattern or "mottled-leaf") varies greatly depending on (i) the time during plant development which it is first manifested, (ii) the extent of its distribution over the leaf, (iii) its intensity , and (iv) the environment. Limited breeding data and selection of different lines from crosses between silvery NJ260 and non-silvery inbreds suggest that several genes play a role in the varied expression of the silvery trait and that this trait is not linked completely with any of the abnormalities of NJ260. Among the environmental influences, light is an important factor. High light energy enhances the expressivity of the silvery trait.

If NJ260 is indeed endowed with an ability to escape natural virus infection, this ability could be due to its silvery foliage. Such a foliage may repel insect vectors in a way analogous to that of aluminum mulch (1). Alternatively, silvery foliage may prevent effective penetration or multiplication of virus particles following contacts with these vectors. However, NJ260 does not appear to resist virus infection following artificial inoculation.

NJ260 is being reproduced this winter in Costa Rica and in Israel. I hope that sufficient seed will be available in the near future for more critical investigations of the silvery trait and its breeding potential with respect to freedom from natural virus infection and plant adaptation.

Literature Cited

  1. Kring, J. B. 1972. Flight behavior of aphids. Ann Rev. Entomology 17:461-492.
  2. Robinson, R. W., H. M. Munger, T. W. Whitaker, and G. W. Bohn. 1976. Genes of the Cucurbitaceae. HortScience 11:554-568.
  3. Scarchuk, J. 1954. Fruit and leaf characters in summer squash. J. Hered. 45:295-297.
  4. Scarchuk, J. and J. M. Lent. 1965. The structure of mottled-leaf summer squash. J. Hered. 56:167-168.
  5. Scott, D. H., and M. E. Riner. 1946. A mottled-leaf character in winter squash. J. Hered. 37:27-28.
  6. Shifriss, O. 1966. Behavior of gene B in Cucurbita. Veg. Improvement Newsletter 8:7-8.
  7. Shifriss, O. 1981. Origin, expression, and significance of gene B in Cucurbita pepo L. J. Amer. Soc. Hort. Sci. 106:220-232.
Home About Membership Reports Gene Lists Conferences Links Search NCSU
Department of Horticultural Science Box 7609North Carolina State UniversityRaleigh, NC 27695-7609919-515-5363
Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 1 August, 2007