Pollen Germination Characteristics under Temperature and Relative Humidity Treatments for Artificial Pollination of Apples

Artificial pollination is commonly used to increase the amount and quality of apple production because inclement weather during flowering adversely affects the apple fruit set in Korea. However, the effectiveness of artificial pollination depends on meteorological conditions. Thus, this study was carried out to investigate the effects of temperature (0, 5, 10, 15, 20, 25 and 30°C) and relative humidity (30, 50 and 80%) on the pollen germination rate and pollen tube growth of ‘Hongro’, ‘Tsugaru' or mixed ‘Crabapple’, which were used to pollinate ‘Fuji’ apple. Both the pollen germination rate and pollen tube growth were better at 20 and 25°C than at any other temperature. Temperature pretreatment had a significant influence on pollen germination. High germination rates (58.2–72.4%) were obtained at 15–30°C with ‘Tsugaru’ and ‘Hongro’ pollen, but sharply decreased to 34.8% and 40.3% at 35°C, respectively. Mixed ‘Crabapple’ pollen showed a pollen germination rate of 70.6–79.5% at a temperature of 15–30°C and a germination rate of 58.4% at 35°C. When ‘Crabapple’ pollen was applied liberally to king flowers of ‘Fuji’ and ‘Hongro’ under different relative humidity treatments, a higher relative humidity resulted in greater pollen tube elongation based on pollen tubes that reached the base of the style. The number of pollen tubes that reached the base of the style in ‘Fuji’ increased to 3.69 at 80% compared to 2.21 at 30% relative humidity. Similarly, the number pollen tubes reaching the base of the style in ‘Hongro’ was 5.78 at 80% relative humidity.