Cucurbit Genetics Cooperative Report 5:33-34 (article 17) 1982
C. D. Zack and J. B. Loy
University of New Hampshire, Durham, NH 03824
Studies by Mann (1) indicated that injury to the flower during emasculation inhibited fruit set. Experiments by Natti and Loy (2) showed that excised emasculated flowers produce 2 to 3 times as much ethylene as non-emasculated flowers during the first 6 hours following emasculation at anthesis. Aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, suppressed wound ethylene production and also increased fruit set in emasculated, hand-pollinated flowers. Although the results of the above study suggested that wound ethylene might play a role in lowering fruit set in hand-pollinated muskmelon, they did not rule out AVG promoting of fruit set by lowering normal endogenous concentrations of ethylene in the ovary and style.
Experiments were conducted in the field during the summer of 1979 to further test the effect of ethylene on fruit set. The following lanolin paste treatments were applied to the base of corollas of cv. Minnesota Midget at anthesis using pollination and treatment techniques described previously (2): open-pollinated control (lanolin paste only), non-emasculated +5 µg AVG in lanolin paste, non-emasculated + 0.1 µg ACC in lanolin paste, emasculated control (lanolin paste only), emasculate +5 µg AVG and emasculated + 0.1 µg ACC (1-aminocyclopropane-1-carboxylic acid) is an ethylene precursor, and 0.1 µg per flower raised ethylene production in excised non-emasculated flowers above that of emasculated flowers. AVG at 5 µg lowered ethylene production in emasculated flowers below that of non-emasculated flowers.
Emasculation lowered fruit set in all cases (Table 1). Neither AVG nor ACC significantly affected fruit set in either emasculated or non-emasculated flowers. We are left with the conclusions that either endogenous ethylene has little effect on fruit set under some conditions, or that site of application of AVG and ACC must be at the base rather than top of the ovary for effectiveness.
Table 1. Effect of ACC and AVG on fruit set of emasculated and non-emasculated brush-pollinated flowers of cv. Minnesota Midget.
Treatment |
No. of pollinations |
% Fruit Set |
| Open-pollinated | 80 | 78 |
| Non-emasculated +5 µg AVG | 70 | 76 |
| Non-emasculated +0.1 µg ACC | 73 | 71 |
| Emasculated | 107 | 56 |
| Emasculated +5 µg AVG | 69 | 45 |
| Emasculated +0.1 µg ACC | 65 | 44 |
Using field-grown plants and gas chromatographic methods described previously (2), we compared ethylene levels in excised emasculated or non-emasculated flowers from 10 cultivars of muskmelon (Table 2). There was considerably variability in ethylene production from flowers of different cultivars, and cultivars that produced high amounts of ethylene from non-emasculated flowers usually produced correspondingly high amounts from emasculated flowers. Mean ethylene production was always higher in emasculated than in non-emasculated flowers. There was often marked variability in ethylene production among replications, particularly with emasculated flowers, even though care was taken to emasculate uniformly. Perhaps certain flowers, because of position on the plant, produce larger quantities of ethylene which in turn, lowers the probability of fruit set. Interestingly, flowers from the monoecious line, 48-3-9-8-8, produced the least amount of ethylene, and this line generally sets fruit well. We had planned but were unable to obtain sufficient fruit set data to compare against ethylene levels for the cultivars listed in Table 2.
Table 2. Ethylene production by excised emasculated and non-emasculated flowers of several muskmelon cultivars. Data represent mean for 5 replications.
µl ethylene/flower/6 hr |
||
Cultivar |
Non-emasculated |
Emasculated |
| Minnesota Midget | 1.69 ± 0.28 | 2.25 ± 0.45 |
| Delicious 51 | 1.20 ± 0.22 | 4.43 ± 1.46 |
| 45-Early Crown Set | 3.30 ± 1.32 | 7.44 ± 4.35 |
| 53-1-4-12 (breeding line) | 1.72 ± 0.16 | 4.96 ± 1.60 |
| Granite State | 1.91 ± 0.33 | 3.63 ± 1.10 |
| Golden Champlain | 1.27 ± 0.53 | 1.77 ± 0.37 |
| Hearts of Gold | 1.55 ± 0.31 | 3.73 ± 1.47 |
| Honey Rock | 2.65 ± 1.09 | 5.31 ± 2.43 |
| Osage | 1.02 ± 0.13 | 1.18 ± 0.25 |
| 48-3-9-9-8 (monoecious line)z | 0.80 ± 0.09 | 1.21 ± 0.09 |
z Corolla removed as substitute for emasculation.
Literature Cited
- Mann, L.K. 1953. Honeybee activity in relation to pollination and fruit set in the cantaloupe (Cucumis melo). Amer. J. Bot. 40:545-553
- Natti, T.A. and J.B. Loy. 1978. Role of wound ethylene in fruit set of hand-pollinated muskmelons. J. Amer. Soc. Hort. Sci. 103:834-836.