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
- Kring, J. B. 1972. Flight behavior of aphids. Ann
Rev. Entomology 17:461-492.
- Robinson, R. W., H. M. Munger, T. W. Whitaker, and G.
W. Bohn. 1976. Genes of the Cucurbitaceae. HortScience 11:554-568.
- Scarchuk, J. 1954. Fruit and leaf characters in summer
squash. J. Hered. 45:295-297.
- Scarchuk, J. and J. M. Lent. 1965. The structure of
mottled-leaf summer squash. J. Hered. 56:167-168.
- Scott, D. H., and M. E. Riner. 1946. A mottled-leaf
character in winter squash. J. Hered. 37:27-28.
- Shifriss, O. 1966. Behavior of gene B in Cucurbita.
Veg. Improvement Newsletter 8:7-8.
- Shifriss, O. 1981. Origin, expression, and significance
of gene B in Cucurbita pepo L. J. Amer. Soc.
Hort. Sci. 106:220-232.
