Factors affecting the quality and in vitro germination capacity of strawberry pollen

Abstract

SummaryPoor pollen quality and germination capacity curtails early yield in strawberry. The aim of this study was to establish a reliable method for in vitro assessment of strawberry pollen germination ability and to investigate further the effects of photoperiod and gibberellin on pollen germination and quality. In the first part of the study, pollen from seven strawberry cultivars (Chandler, Selva, Tudla, Camarosa, Eris, Pajaro and Irvine) was collected and its germination capacity and incidence of deformed pollen grains assessed in vitro using the hanging-drop technique. Highest germination rates, in ‘Selva’, were observed in a nutrient medium of 10% sucrose. Addition of calcium nitrate to the medium decreased the germination percentages of all cultivars. There was no significant difference, on average, between the germination rate at 20° and 25°C. Genetic factors affected the incidence of deformed pollen grains significantly, with ‘Pajaro’ showing the highest percentage (76%). In the second part, groups of young strawberry plants, cultivar Seascape, grown either under natural early spring conditions or under long-day or short-day conditions were sprayed once with GA3 at 0, 50, or 200 mg l–1. Pollen germination and deformation and stamen length were assessed three months later. In plants of the first group, GA3 at 50 mg l–1 increased pollen germination and decreased the incidence of deformed pollen grains, while GA3 at 200 mg l–1 decreased pollen germination without affecting the formation of deformed pollen grains. Plants of the second group showed a higher rate of pollen germination under long than under short days. GA3 at 200 mg l–1 decreased pollen germination under either short- or long-day conditions compared with the controls but doubled the percentage of deformed pollen only under short days. Stamens in control plants grew four times as long under long- than short-day conditions. GA3 did not affect stamen length under long days but significantly enhanced their growth under short days.