Cucurbit Genetics Cooperative Report 1:36-37 (article 33) 1978
Claude Heit, R. W. Robinson, and W. Mishanec
New York Agricultural Experiment Station, Geneva, NY 14456
Dormancy is seldom a serious problem with seed of cucumber and muskmelon. Freshly harvested seed may be dormant, but this can usually be easily overcome by removal of the seed coats or by storage after harvest. Seeds of certain other Cucumis species, however, have a dormancy that does not respond to aging or seed coat removal. Interspecific hybridization experiments were hampered by the seed dormancy of these species, prompting this investigation to find a suitable method to break dormancy.
Seed of different Cucumis .species were placed on blotters in Petri dishes at constant 20°C in darkness to determine the extent of seed dormancy. Species that were not dormant, but germinated within a week, included Cucumis africanus var. anguria, C. anguria var. longipes, C. dipsaceus, C. heptadactylus, C. hirsutus, C. melo, C. metuliferus, C. prophetarum, C. sativus, C. sativus var. sikkimensis, C. trigonus, and C. zeyheri. Species that did not germinate in this experiment were C. africanus, C. ficifolius, C. leptodermis, and C. myriocarpus.
One year old seed of PI 264217, an accession of C. myriocarpus, was selected for further study. Pretreating the seed for 8, 16, or 24 hours with 5% H2O2, scarification by nicking the seed coat or by 30 minutes immersion in sulfuric acid, variations in moisture on the germination blotter, and applications of KNO3 or 2, 50, or 500 ppm gibberellic acid did not improve germination. Little response was noted to light, but temperature treatments were very effective for breaking dormancy (Table 1). Seed was dormant at low temperature, but germinated at warm temperature. Seeds dormant after 4 weeks at 15°C had 93% germination within a week after the temperature was increased to 25°C. Good germination was achieved with diurnal variation in temperature, fluctuating at 12-hour intervals from 30°C to 10 or 20°C. Prechilling the seed at 3-5°C improved germination, but prolonged prechilling was insufficient to overcome the dormancy occurring at low temperature.
The Cucumis species with seed dormancy are of African origin and adapted to tropical conditions. Dormancy at low temperature may have been favored by natural selection to delay germination until conditions are suitable for good growth and development.
Table 1. Influence of temperature and light on germination of Cucumis myriocarpus.
% Germination by days |
||||||
No. days prechilled at 3-5°C |
Germination conditions |
7 |
14 |
21 |
28 |
|
| none | l5°C | light | 0 | 0 | 0 | 0 |
| none | 15°C | dark | 0 | 0 | 1 | l |
| none | 20°C | light | 0 | 0 | 0 | 2 |
| none | 20°C | dark | 0 | 3 | 3 | 9 |
| none | 25°C | dark | 8 | 14 | 15 | 16 |
| none | 10-30°C | light | 8 | 40 | 57 | 78 |
| none | 15-30°C | light | 3 | 9 | 10 | 12 |
| none | 20-30°C | light | 7 | 11 | 16 | 18 |
| none | 20-30°C | dark | 11 | 20 | 30 | 33 |
| 20 | 25°C | dark | 81 | 85 | 87 | – |
| 20 | 10-30°C | light | 90 | 93 | 93 | – |
| 20 | 20-30°C | light | 74 | 87 | 88 | – |
| 30 | 25°C | dark | 83 | 88 | 90 | – |
| 30 | 10-30°C | light | 40 | 72 | 91 | – |
| 30 | 20-30°C | light | 86 | 90 | – | – |
| 45 | 20°C | light | 4 | 10 | 11 | 12 |
| 45 | 20°C | dark | 31 | 34 | 38 | 43 |
| 45 | 25°C | dark | 89 | 90 | 90 | – |
| 45 | 10-30°C | light | 70 | 83 | 87 | – |
| 45 | 20-30°C | light | 78 | 81 | – | – |
| 150 | 15°C | light | 0 | 1 | 4 | 4 |
| 150 | 20°C | light | 0 | 10 | 12 | 12 |
| 150 | 10-30°C | light | 70 | 78 | 80 | 81 |
| 150 | 20-30°C | light | 76 | 82 | 82 | 82 |