Apple Pollen Tube Growth Rates Are Regulated by Parentage and Environment

in Journal of the American Society for Horticultural Science

A greater understanding of apple (Malus ×domestica) pollen tube growth rates can improve crop load management in commercial orchards. Specifically, applications of caustic bloom-thinning chemicals need to occur when enough, but not too many, flowers have been fertilized to achieve crop load densities that balance yields with marketable fruit sizes. In this study, the pollen tube growth rates of five crabapple (Malus sp.) cultivars were measured in the styles of three maternal cultivars at 12, 18, 24, and 30 °C after 24 hours in a growth chamber. Pollen tube growth rates were greatest for ‘Selkirk’ and ‘Thunderchild’ at 12 °C, and greatest for ‘Indian Summer’, ‘Selkirk’, and ‘Thunderchild’ at 24 °C. Pollen tube growth increased with increasing temperatures until 24 °C. There were minimal pollen tube growth rate increases between 24 and 30 °C. Overall, ‘Snowdrift’ had the slowest pollen tube growth rate of the five evaluated crabapple genotypes. At 24 and 30 °C, ‘Indian Summer’ and ‘Thunderchild’ pollen tubes reached the base of the style most frequently, and ‘Snowdrift’ pollen tubes the least frequently. Pollen tube growth rate was also influenced by the maternal cultivar, with Golden Delicious having relatively faster pollen tube growth than Fuji at 24 and 30 °C. Interactions among paternal and maternal genotypes as well as temperature after pollination reveal complex biological and environmental relationships that can be used to develop more precise crop load management strategies for apple orchards.

Contributor Notes

This project was funded by Virginia Agricultural Experiment Station and Virginia Tech’s Department of Horticulture.

We thank Abby Kowalski, Ashley Thompson, Taylor Mackintosh, and David Carbaugh for their assistance in the field and lab, Mizuho Nita for guidance with statistics, and Roger Harris and Tony Wolf for review of the manuscript.

Corresponding author. E-mail: gmp32@cornell.edu.

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    ‘Thunderchild’ pollen tube growth in a ‘Fuji’ apple 24 h after pollination at a constant temperature of 24 °C, visualized with water-soluble fluorescent solution containing 0.01% aniline blue dye in 0.067 m K2HPO4 and magnified 10× using a light microscope and a fluorescent light source.

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    Mean apple pollen tube growth length of cultivars Evereste, Indian Summer, Selkirk, Snowdrift, and Thunderchild in all evaluated maternal cultivars (Cripps Pink, Golden Delicious, and Fuji combined) styles 24 h after pollination in growth chambers kept at (A) 12 °C and (B) 24 °C. Statistical analysis by analysis of variance and post hoc mean separation by Tukey’s honestly significant difference (JMP). Each value represents 105 observations. Error bars represent se.

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