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Cucurbit Genetics Cooperative Report 16:55-57 (article 20) 1993

Genetic Parthenocarpy in Cucurbita Pepo L.

R.W. Robinson

Horticultural Sciences Department, New York State Agricultural Experiment Station, Geneva, New York 14456

Fruit set of summer squash can be very poor when conditions are unfavorable for pollination. Many F1 hybrid cultivars have been bred to have a high ratio of female to male flowers and they may not have sufficient male flowers for good pollination at all times. The problem of poor fruit set is especially acute early in the season when prices are highest, but production may be limited because the low temperature, long day length, and high light intensity of that season promotes female sex expression and reduces male flower formation. Genetic parthenocarpy would be of value in situations where male flower production is insufficient and could also increase yield when there are insufficient bees for good pollination, when bee activity is restricted by wet weather, and when pollinating insects are kept away from squash blossoms by plastic tunnels or other row coverings. If row covers did not need to be opened or removed for pollination, they could be left on squash plants longer to improve growth and early yield ny increasing the temperature around the squash plants, and also reduce losses from insects and insect-transmitted virus diseases.

Genetic differences in Cucurbita pepo for ability to set parthenocarpic fruit were reported by den Nijs and Veldhuyzen den Zanten (1982). They found that early production of parthenocarpic fruit ranged from none for some cultivars to 42% for 'DG-4'. Previously, Rylski (1972) noted that 'Zucchini Elite' had a stronger parthenocarpic characteristic than 'Bushy White'.

For the past three years we have been selecting for genetic parthenocarpy in the summer squash breeding program at Geneva, NY. Several CMV resistant breeding lines, including 82-138 and 82-141, compared favorably with 'DG-4' for parthenocarpic fruit set. Preliminary tests this past season, hwoever, indicated that there may already be commercially available cultivars with even better parthenocarpic fruit set than the best of our breeding lines selected for parthenocarpy.

Thirty-three C. pepo cultivars and breeding lines were grown in the field and the first female flowers to develop on each plant were enclosed in paper bags before anthesis to prevent insect pollination. The number of female flowers closed for each cultivar or line is given in Table 1. Only fruit that developed to a marketable stage were recorded as being set parthenocarpically, and fruit that had some ovary enlargement, then turned brown and ceased development were not regarded as set. The fruit that were considered parthenocarpic had normal size and shape, and at maturity contained no seeds.

Two thirds of the entries in the trial set parthenocarpic fruit, the best being 'Chefini Hybrid" with 82% fruit set (Table 1). It is not known if the unusually cool and wet season of 1992 in New York was a factor in the extraordinary set of parthenocarpic fruit by some cultivars.

Many summer squash cultivars with the same fruit color have a similar gene background and may have similar incidence of parthenocarpy. It was previously reported (1, 2) that zucchini-type cultivars have beetter parthenocarpic fruit set than yellow- or white-fruited cultivars. That was generally true in our test, but there were exceptions. Green-fruited 'Ambassador', for example, was relaively poor in parthenocarpic fruit set in our trial and also in Holland (1), and none of the five female flowers we tested for 'Dark Green Zucchini' set fruit, but the yellow-fruited cultivar Gold Strike had excellent set of parthenocarpic fruit. Results from our breeding program and cultivar tests indicate thatit should be possible to breed parthenocarpic squash of different fruit colors and types.

Table 1. Parthenocarpic fruit set of squash cultivars and lines.

Cultivar or Line
Type
No. female flowers tested
% Parthenocarpy
Chefini Hybrid
zucchini
11
82
Gold Strike
yellow straightneck
8
75
Black Beauty
zucchini
7
71
Black Magic
zucchini
9
67
NY-82-138
zucchini
2
50
NY-92-728
zucchini
7
43
Green Magic
zucchini
12
42
NY-82-141
zucchini
8
38
Gold Slice
yellow straightneck
6
33
Cocozelle
striped straightneck
7
29
Goldie Hybrid
yellow crookneck
17
29
President
zucchini
14
29
Black Jack
zucchini
16
25
Gold Rush
precocious yellow straightneck
10
20
Caserta
striped straightneck
17
18
Golden Girl
yellow straightneck
12
17
Onyx
zucchini
7
14
Senator
zucchini
14
14
NY-92-727
zucchini
14
11
Hyrific
yellow straightneck
9
11
White Scallop
white scallop
9
10
Ambassador
zucchini
10
0
Yellow Crookneck
yellow crookneck
8
0
Gold Bar
yellow straightneck
10
0
Honey Boat
Delicata winter squash
4
0
Multi Pik
precocious yellow straightneck
12
0
Peter Pan
green scalop
11
0
Royal Acorn
green acorn winter squash
5
0
Scallopini
gren scalop
9
0
Slendegold
yellow straightneck
6
0
Early Prolific Straightneck
yellow straightneck
5
0
Dark Green Zucchini
zucchini
5
0
NY-92-730
zucchini
6
0

Literature Cited

  1. Nijs, A.P.M. den and N.J.D. Veldhuyzen van Zanten. 1982. Parthenocarpic fruit set in glasshouse grown zucchini squash. Cucurbit Genet. Coop. Rpt. 5:44-45.
  2. Rylski, I. 1974. Effects of season on parthenocarpic and fertilized summer squash (Cucumis pepo l.). Expl. Agric. 10:39-44.
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