Cucurbit Genetics Cooperative Report 6:91 (article 46) 1983
Influence of Temperature and Humidity on Longevity of Squash Pollen
Yong-Jian Wang and R. W. Robinson
Seed and Vegetable Sciences Department, New York State Agricultural Experiment Station, Geneva, NY 14456
It would be convenient in squash breeding to store pollen for extended periods, particularly with late maturing or photoperiodic germplasm that does not flower sufficiently early to permit field pollinations. With many crops, pollen can be stored for six months or more in a desiccator kept in a freezer. We were unsuccessful, however, when we stored squash pollen in this way.
Pollen was germinated in Brewbaker and Kwack (1) medium with a modified sucrose concentration of 15% in order to investigate the influence of storage conditions on longevity of 'Early Prolific Straightneck' squash pollen. Good germination was obtained with fresh pollen, but it remained viable for only 4 hours in a CaCl2 desiccator kept in a freezer at -20°C. Pollen kept at the same temperature but not in a desiccator had an equally short storage life.
Squash pollen is a very sensitive to low humidity as well as freezing. When stored in a growth chamber at 30°C, pollen kept at ambient (46%) relative humidity lost viability within 2 hours, but pollen at 100% RH and the same temperature still had good germination after 5 hours storage.
The rapid loss of pollen viability at high temperature and low humidity raised questions about our field pollination procedure, in which closed staminate flowers collected at 7 am are stored in paper bags under even more adverse field conditions, and used for pollination during the next 5 hours. This procedure appears satisfactory, however, since the humidity within the flower is sufficiently high to protect the pollen from desiccation. Pollen removed from anthers and stored at 30°C and ambient humidity had only 5% germination after 2 hours storage, but pollen kept under the same conditions except for not being detached from the anther had as good (55%) germination after 5 hours as detached pollen stored at 100% RH and 30°C.
Tests to prolong pollen longevity by storage in organic solvents (acetone, petroleum ether, or dimethyl sulfoxide), in nitrogen atmosphere, or by quick-freezing in dry ice dissolved in acetone were not successful. Although none of the treatments permitted pollen from the field to be stored long enough to be used in winter greenhouse pollinations, pollen storage for short periods is possible and can be useful in squash breeding, particularly for crosses with plants not flowering simultaneously. A simple and effective procedure is to collect male flowers the day before anthesis, store them on moist blotters in a sealed container in a refrigerator until the female parent flowers, and then keep them at room temperature for an hour to induce dehiscence. Crosses can be made between plants flowering up to 2 weeks apart in this way.
- Brewbaker, J. L. and B. H. Kwack. 1967. The essential role of calcium ion in pollen germination and pollen tuber growth. Amer. J. Bot. 50:859865.