Cohen, E., Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel
Lavi, U., Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel
Spiegel-Roy, P., Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet Dagan 50-250, Israel

Papaya pollen viability, tube growth and storage were studied. Pollen germination on a drop of modified Brewbaker medium at 22-26°C closely reflected in vivo germination. Two vital stains gave pollen viability estimates that correlated closely with pollen germination percentage. The time from pollination to first ovule penetration was 25 h at 28°C, no in vitro pollen germination was observed at 5°C and at 40°C pollen tube growth was retarded. High relative humidity (70-80%) hastened the process compared with low relative humidity (30-40%). Pollen could be stored successfully for 6 months when kept at - 18°C in a deep-freezer. Storage of pollen for the winter months, during which no or very little viable pollen is formed in the coastal area of Israel, seems a practical means to ensure adequate fruit set. © 1989.