Male and female interaction in apple: Pollen tube growth, fruit set, fruit quality, and return bloom
In apple, adequate and appropriate pollination and fertilization is required for fruit set, fruit quality and subsequent fruit growth. Pollen source, pollen-style interaction and compatibility, and ample pollen tube growth are potentially highly influential factors on the fertilization and fruit setting process. Pollinizer is considered to be one of the influential factors and has a remarkable impact on fertilization. However, basic information on the level of pollinizer compatibility and its contribution to yield is lacking for many commercial apple cultivars. Hence, we conducted these experiments to compare pollinizers in terms of pollen tube growth, fruit set, fruit quality and return bloom. Honeycrisp, Gala, and Fuji cultivars were hand-pollinated by Crabapple, Red Delicious or Golden Delicious pollen. Pollen source had a significant influence on pollen tube growth and pollen tube enrichment in to the base of the style. Golden Delicious pollen had the highest and fastest growth followed by Red Delicious and Crabapple. Crabapple was not an effective pollinizer for Honeycrisp resulting in low fruit set, but both Red Delicious and Golden Delicious were adequate pollinizers of Honeycrisp apples. Pollen tube growth increased overtime 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 significantly positive correlation was found between pistil number and seed number indicating that reducing pistil number is an effective experimental tool to regulate seed number. The percent return boom was dramatically decreased with increasing individual fruit fresh weight. Likewise, percent 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 design. Based on our findings, we recommend growers to do not plant Ralph-Shay or Malus floribunda Crabapples as pollinizers for Honeycrisp.
Hirst, Purdue University.
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