Male and Female Interaction in Apple: Pollen Tube Growth, Fruit Set, Fruit Quality, and Return Bloom

Optimal apple production requires adequate and appropriate pollination and fertilization in order to set fruit, increase fruit quality and productivity. Pollen source, pollen-style interaction and compatibility, and pollen tube growth determine the degree of fruit-set. Despite the importance of pollination, basic information on pollen compatibility and effect on yield is lacking for many commercial apple cultivars. Thus, these experiments were conducted to compare pollinizers in terms of pollen tube growth, fruit set, fruit quality and return bloom. Honeycrisp, Gala, and Fuji flowers were hand-pollinated by crabapple (Malus floribunda and Ralph Shay), Red Delicious or Golden Delicious pollen. Pollen source had a significant influence on pollen tube growth and pollen tube enrichment to the base of the style. Golden Delicious pollen had the highest and fastest growth followed by Red Delicious and Crabapple. Both crabapple cultivars tested were not effective pollinizers for Honeycrisp resulting in slow pollen tube growth and low fruit set. Red Delicious and Golden Delicious, however, were adequate pollinizers of Honeycrisp apples. Pollen tube growth increased over time after pollination and generally reached the base of the style 96 hours after pollination. Fruit quality attributes and return bloom were generally not affected by pollen source. However, crabapple pollen resulted in the lowest number of seeds per fruit in all cultivars. Seed number was positively correlated with Gala and Honeycrisp fruit fresh weight regardless of the pollen source. A significant positive correlation was found between pistil number and seed number indicating that reducing pistil number is an effective experimental tool to regulate seed number. Return boom was dramatically decreased with larger individual fruit fresh weight. Likewise, return boom was reduced with increasing seed number per fruit. These results suggest that pollen source and seed number per fruit influence fruit set, fruit quality, and biennial bearing potential of Honeycrisp. This has real world implications for orchard establishment and management.