Troubles in pear pollination: Effects of collection and storage method on pollen viability and fruit production

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Pear trees require insect pollination among compatible cultivars to set fruit. However, pollen transfer limitation is the main cause of poor yields in this species, due to low visitation rates and few pollen transfer among compatible cultivars. Assisted pollination using “pollen dispensers” containing precollected compatible pollen fitted into the opening of a beehive could increase yield. We investigated whether stored pollen collected from flowers or bee visitors is suitable for pollinating two European pear (Pyrus communis) cultivars, ‘Conférence’ and ‘Doyenné du Comice’. Pollen collected directly from flowers and indirectly from insects was stored for up to 1 year at 4 °C and −20 °C. Pollen stored at −20 °C showed high viability for both cultivars (60–72%). Consequently, fruit set and fruit diameter using this pollen for pollination was similar to that of fresh pollen. However, the viability of pollen that had been stored at 4 °C was low (6%–14%) and fruit diameter was 6.5% lower when flowers were pollinated with pollen stored at 4 °C compared to fresh pollen. The viability of bee-collected pollen was up to 62% lower than that of pollen collected from flowers. The use of bee-collected pollen as a pollen source resulted in a 48% lower fruit set and 95% lower seed set in ‘Conférence’ compared to fresh pollen, whereas it did not affect ‘Doyenné du Comice’ fruit and seed sets. The fruit diameter was smaller when flowers were pollinated with bee-collected pollen than with fresh pollen in both ‘Conférence’ (54.7 vs. 60.6 mm) and ‘Doyenné du Comice’ (62.5 vs. 70.0 mm). Therefore, pear pollen collected from flowers and stored at −20 °C could successfully be used for alternative pollination without affecting fruit production.