Effect of pre-incubation humidity and temperature treatment on the in vitro germination of avocado pollen grains

Optimum in vitro germination of pollen grain of the avocado cultivars Fuerte, Nabal, Ettinger, Bacon and Zutano occurred at 25 degrees C. However, there were significant differences between cultivars in percentage germination and relative humidity (RH) requirements for optimum pollen grain growth. The most sensitive cultivar to relative humidity was Fuerte, in which the germination of pollen grain rose from 11.4%, at 40% RH, to about 50%, after one hour at 100% RH. The germination% of Nabal pollen grain was already high at 40% RH and was not increased by higher relative humidity. Increased relative humidity also helped to sustain the viability of avocado pollen. At 30 degrees C and 5% RH the pollen grain of Fuerte quickly lost its ability to germinate, at 40% RH for 1 hour, germination was reduced spectacularly compared to pollen kept in saturated with moisture environment where it was not affected the first 24 hours. The effects of temperature and relative humidity on fruit-set and yield of avocado are discussed.