Cucurbit Genetics Cooperative Report 5:44-45 (article 22) 1982
A.P.M. den Nijs and N.J.D. Veldhuyzen van Zanten
Institute for Horticultural Plant Breeding, P.O. Box 16, Wageningen, The Netherlands
Zucchini squash is grown in the Netherlands in glasshouses in spring and fall. The crop has limited importance so far (annual sales less than a million guilders), but it has potential for increased production. The major drawback, especially for the spring culture (planting in February/March) is the necessity of pollinating for normal fruit development. Bees kept in the glasshouse for pollinating are inactive under the prevailing cloudy and cool conditions and hand pollination is very laborious. Chemical stimulation of parthenocarpic fruit set has not proved practical.
Genetic parthenocarpy would eliminate the need for pollination. Besides it may allow a change in sex-expression towards more completely female cultivars which may produce an even earlier crop. In addition the growth of parthenocarpic fruits could be less exuberant, resulting in less competition between plant parts and more flexibility in harvesting schedules. Rylski (3), when studying the effects of temperature and light on the tendency to parthenocarpic fruit set of two summer squashes, detected a strong difference between them. She also confirmed (4) earlier observations (1, 2) on the positive effect of low night temperature. This low night temperature being recommended for glasshouse production in the Netherlands, we decided to take a practical approach by screening a collection of cultivars for parthenocarpic fruit development when grown at low night temperature. This report gives results of one such trial involving 19 cultivars in the spring of 1981.
The plans were grown at 75 cm distance in rows 150 cm apart in an insect-proof Venlo-type glasshouse. Seeds were sown February 13, planting was March 5. Temperature was set at 17°C D / 10°N. Five plants of each cultivar were randomly arranged in 3, 4, or 5 repetitions. Biweekly harvests of parthenocarpic fruits started April 13 and were terminated May 11. Individual male and female flowers were counted from March 31 until April 17, and all fruits of all 8 harvests were counted, weighed, and classified for quality. Only normal-shaped, regular-sized fruits were assigned to quality class 1. All partly developed fruits (with e.g. tapering ends) were placed in lower quality classes. Many of these fruits suffered from blossom-end rot, initiated by rotting of the non-dehisced flower. From the number of fruits per plant in the earliest harvests (until April 24) and the mean number of female flowers per plant until April 17, the percentage early parthenocarpic fruit set was calculated (see Table 1).
Clear differences in the parthenocarpic fruit yield are evident from the table, in the earliest harvest as well as for the combined first four weeks of harvest. Only three cvs. yielded three fruits or more per plant. Only four cvs. attained more than 1000 grams of total fruit weight per plant. Most parthenocarpic cvs. are in the early and medium maturity groups. The percentage first quality fruits was not correlated with the degree of parthenocarpy. ‘Black Jack,’ DG-4, ‘Baroz’ and 605 produced a good share of first quality fruits, DG-4 and ‘Black Jack’ had the highest actual yield of such fruits.
The ranking of cultivars according to parthenocarpic fruit set in this trial corresponded quite well with that from a similar trial in 1980. In that experiment cv. Dark Green Zucchini (by Otis Twilley Seeds Co.) stood out because of high yields of first quality fruits. Several plants of this cv. were selfed, but only one line, DG-4 could be included in the present trial. Unfortunately the original cv. could not be planted because of lack of seed.
The outstanding yield of the line testifies to the hereditary basis of the character which can apparently be fixed. This holds promise for breeding of zucchini squash with increased parthenocarpic fruit set in glasshouses. We cannot involve ourselves in such a program at the Institute. Remnant seed of the line DG-4 and related materials are available to interested breeders.
Table 1. Parthenocarpic fruit set per plant of zucchini squash cultivars.
Fruits set until 24-4-81 |
Fruit set until 11-5-81 |
|||||
Cultivar (group) (early) |
Fruit type* |
Number |
Percent |
Number |
Yield |
Percent class 1
|
| 605 | d. | 0.7 | 17 | 2.6 | 944 | 52 |
| DG-4 | d. | 1.8 | 42 | 4.1 | 1420 | 66 |
| Poseidon | d. | 0.9 | 24 | 3.6 | 1391 | 33 |
| Baroz | 1. | 0.4 | 4 | 2.2 | 588 | 54 |
| Cocozelle (medium) | 1. | 0.7 | 27 | 3.0 | 1101 | 43 |
| Black Jack | d. | 0.1 | 9 | 2.6 | 1011 | 77 |
| Diamant | d. | 0.4 | 8 | 1.7 | 371 | 17 |
| Storr’s Green | d. | 0.1 | 4 | 1.1 | 398 | 27 |
| Burpee Hybrid | d. | 0.1 | 3 | 0.5 | 182 | 75 |
| Elite | d. | 0.3 | 8 | 0.8 | 424 | 58 |
| Fordhook | d. | 0 | 0 | 1.3 | 629 | 69 |
| Clarita | 1. | 0.2 | 3 | 1.1 | 326 | 71 |
| Greyzini | 1. | 0.1 | 3 | 0.7 | 240 | 55 |
| Bassar | 1. | 0.1 | 1 | 2.0 | 373 | 13 |
| Marba (late) | 1. | 0.1 | 3 | 0.6 | 257 | 88 |
| Ambassador | d. | 0 | 0 | 1.2 | 365 | 19 |
| Aristocrat | d. | 0 | 0 | 0.3 | 45 | 60 |
| Gourmet Globe | r. | 0 | 0 | 0.2 | 59 | 33 |
| White Bush | w. | 0 | 0 | 0.1 | 7 | 0 |
*d. = dark green, 1. = light green, r. = round, w. = white.
Literature Cited
- Nitsch, J.P.. E.B. Kurtz, J.L. Liverman and F.W. Went, 1952. The development of sex expression in cucurbit flowers. Amer. J. Bot. 39: 32-43.
- Globerson, D. 1971. Effects of pollination on set and growth of summer squash ( Cucumis pepo) in Israel. Expl. Agric. J. 7:183-188.
- Rylski, I. 1974. Effects of season on parthenocarpic and fertilized summer squash (Cucumis pepo L.) Expl. Agric. J. 10:399-440.
- Rylski, I. 1974. Fruit set and development of several vegetable crops grown under low temperature conditions. Proceedings XIX Intl. Hort. Congr. Warszawa, Vol. III: 375-385.