Pollen Performance Differs Among Cultivars of Northern Highbush Blueberry ( Vaccinium CorymbosumL.)

Pollen performance (i.e., germination, viability, and tube growth) in highbush blueberry ( Vaccinium corymbosumL.) is not well characterized across commercially important cultivars and under environmental conditions typical for pollination-limited western Washington, U.S. Cultivars may differ in pollen performance and how they respond to environmental conditions, which may impact ovule fertilization and subsequent berry development. Knowing intrinsic cultivar differences in tetrad germination rates and threshold environmental conditions that impact pollen performance may help growers implement targeted strategies that are being tested and developed to improve pollination and berry development. In this study, the main objective was to evaluate pollen performance by measuring pollen germination rate, tube length, and tube number per tetrad among four commercially important highbush blueberry cultivars under five different temperature conditions. ‘Aurora’, ‘Draper’, ‘Duke’, and ‘Liberty’ blueberry pollen were collected every week from 5-100% bloom in 2018 and incubated in vitroat 2, 7, 13, 18, and 24 °C for 4 days, which was when pollen growth ceased. Tetrads were observed using a microscope every 24 hours. Pollen germination rate, tube length, and tube number per tetrad were determined. Results showed that the optimal temperature range to reach maximum pollen germination, tube length, and tube number per tetrad in vitrois 13-24 °C for ‘Aurora’, ‘Draper’, and ‘Duke’, but 13-18 °C for ‘Liberty’. ‘Liberty’ had a relatively lower pollen germination rate and tube growth than the other evaluated cultivars. ‘Liberty’ was also more sensitive to low and high temperatures. These observations suggest that some of the pollination and fruit development challenges with ‘Liberty’ may be due to the biology of the pollen itself, as it exhibited a reduced capacity to germinate and grow. These data also demonstrate pollen performance differs across commercially important cultivars of highbush blueberry and suggest developing cultivar-specific effective pollination period models may be useful. Additionally, these findings indicate breeders should consider phenotyping pollen characteristics to better understand adaptation and potential intrinsic pollination constraints at the genetic level.