Pollen Source Effects on Seed Number, Fruit Quality and Return Bloom of Apple

Pollen source, seed set and subsequent seed development are necessary prerequisites for apple fruit production. Pollinizer genotype in particular can have a remarkable impact on fertilization and therefore seed set. However, there is little information published on the most effective and compatible pollinizers for particular commercial cultivars. This study was conducted to determine the effect of three pollen sources, crabapple ('Ralph Shay' in 2013 and Mains floribunda in 2014), 'Delicious', and 'Golden Delicious' on seed number, fruit quality and subsequent return bloom of 'Honeycrisp', 'Fuji' and 'Gala' apples. The effects of 'Gala' pollinizing 'Honeycrisp' trees were also investigated. There was no effect of pollen source on fruit fresh weight, soluble solids concentration or starch pattern index. Seed number per fruit and seed fresh weight per fruit were significantly influenced by pollen source. When 'Ralph Shay' or Malus floribunda crabapples were used as pollinizers, fruit contained fewer seeds and lower seed fresh weight compared with 'Delicious', 'Golden Delicious' and 'Gala' pollinizers; however, the trend was not statistically significant for all cultivars and years. Fruit fresh weight increased linearly with seed number. Pollen source had no influence on return bloom regardless of female cultivar or year. Return bloom was negatively related to fruit fresh weight and seed number per fruit. These results indicate that pollen source and seed number per fruit influence fruit set, fruit quality, biennial bearing potential of 'Honeycrisp', and therefore should be factors that are considered in the orchard design process. Based on our findings, we recommend growers to do not plant 'Ralph Shay' or Mains floribunda crabapples as pollinizers for 'Honeycrisp'.