Date of Award
Master of Science
Plant, Soil and Environmental Sciences
David L. Coffey
Homer D. Swingle, Gary M. Lessman
The plant growth regulator 2-chloroethylphosphonic acid (ethephon) was applied to four summer squash cultivars to determine its effects on yield and flowering habits. Four ethephon rates, three application regimes, and two locations were used in field studies. Flowering patterns were examined for two cultivars under early fall greenhouse growth conditions. Four ethephon rates and four stages of plant growth for ethephon application were utilized in the greenhouse study. Ethephon levels of 150, 300, and 600 ppm were tested in field studies. The 150 ppm level resulted in the highest yields with the least amount of quality reduction as defined by percentage of fruit marketable. The 600 ppm level resulted in the highest percentage of unmarketable fruit, especially for Zucchini cultivars. Fruit quality was lowered by inadequate pollination, and supplemental pollen sources planted near ethephon treated plants helped alleviate the problem. Average fruit weight was lowered by ethephon for about two weeks after treatment. In field studies, ethephon at the 150 ppm rate applied at the three-leaf stage resulted in higher early yields than did the control in all cultivars. 'Early Prolific' (a yellow open-pollinated cultivar), 'Dixie' (a yellow hybrid cultivar), 'Aristocrat' and 'Senator' (Zucchini cultivars) exhibited early yield increases of 540, 58, 51, and 150 per cent respectively with the 150 ppm, three-leaf stage ethephon treatment. Only Senator exhibited a season total yield increase (32 percent) resultant from ethephon treatment. Ethephon treatment resulted in an increase in total fruit number but not total yield for Early Prolific. Split application of 150 or 300 ppm ethephon were no more successful in increasing yields than were single, three-leaf stage applications of these treatments. Plants treated with split applications tended to distribute yields throughout the season rather than concentrating them at the early part of the harvest period, thereby exhibiting a yield pattern similar to that of control plants. Ethephon levels of 75, 150, and 300 ppm resulted in about the same total numbers of pistillate flowers as did the control for either Early Prolific or Dixie plants grown under early fall greenhouse conditions. However, due to a shortage of staminate flowers, all ethephon treated plants had significantly fewer pollinated pistillate flowers than did control plants. Numbers of pistillate primordia which formed on plants but aborted prior to reaching the flowering stage were 307 to 382 percent higher for Early Prolific plants treated with 75 and 300 ppm ethephon respectively than for control plants. Plants treated with ethephon at the first flower stage had more fruit formed partheno-carpically than did control plants or those treated at the seed stage (seeds were soaked in ethephon for 30 minutes prior to planting) or first fruit stage.
Best, John Oscar, "Effects of ethephon on sex expression and yields of summer squash. " Master's Thesis, University of Tennessee, 1974.