Cucurbit Genetics Cooperative Report 2:40-41 (article 25) 1979
C. D. Zack and J. B. Loy
University of New Hampshire, Durham, NH 03824
Bush strains of Cucurbita maxima squash exhibit a compact form of growth under field conditions during the summer, but grow in a vining manner during the fall and winter in the greenhouse in Durham, NH. Bush-vine heterozygotes exhibit changes in growth pattern, even within a single growing season. This pattern is characterized by a bush type of early growth, followed by a vining habit at a later stage of development. Shifriss (2) attributed this growth response to a “developmental reversal of dominance” phenomenon.
A growth chamber study using incandescent and fluorescent lights revealed that the quality of light prior to a dark period rather than photoperiod has a significant effect (P = 0.05) on internode elongation of C. maxima squash (Table 1). Thus, the vining of bush strains in the greenhouse is probably due to the use of incandescent lighting during the evening. Further growth chamber studies using red and far-red light indicate phytochrome involvement in the end-of-day light response in squash, agreeing with similar studies reported for other species (1, 3).
We had observed that vegetative growth in bush strains appeared to be depressed more than vining strains by fruit set and development. Thus, a further field comparison was made of vegetative growth between plants which were allowed to set fruit or those in which female flowers were removed at anthesis.
Both the bush-vine hybrid and bush strain exhibited increased elongation of successive mature internodes; however, the increase was greater in the bush-vine hybrids. Approximately two weeks following pollination and fruit set, rapid fruit development almost completely suppressed leaf initiation in the bush strain, but did not affect vegetative growth of the bush-vine hybrid. Thus, in C. maxima. growth patterns are similar in bush and bush-vine hybrids in the absence of fruiting. The apparent “developmental reversal of dominance” phenomenon can be interpreted as a physiological response rather than a reversal of dominance of a gene.
Table 1. Length of a mature second internode of a bush strain (76-30-11-6) and a bush-vine hybrid (76-30-11-6 x cv. ‘Pink Banana’).
Length (mm) |
||
Treatment |
Bush |
Bush-vine |
| 12 hrs fluorescent | 10.8 | 19.1 |
| 16 hrs fluorescent | 9.4 | 20.9 |
| 11 hrs fluorescent + 4 hrs incandescent | 31.4 | 39.6 |
| LSD (P = 0.05) | 2.7 | 9.9 |
Mean of 5 replications per treatment.
Literature Cited
- Downs, R. J., S. B. Hendricks, and H. A. Borthwick. 1957. Photo-reversible control of elongation of pinto beans and other plants under normal conditions of growth. Bot. Gaz. 118:199-208.
- Shifriss, 0. 1947. Developmental reversal of dominance in Cucurbita pepo. Proc. Amer. Soc. Hort. Sci. 50:330-346.