Seasonal Fluctuations in Pollen Production and Viability in Eggplant and the Quality of Seed-Containing and Seedless (Auxin-Set) Fruits

Abstract

This study investigates the influence of climate on pollen production and viability of two eggplant cultivars cultivated throughout the year in a greenhouse within the Mediterranean basin and the efficacy of auxin application to produce marketable fruit under unfavourable climatic conditions. The pollen yield per flower of both cultivars was highest during November and lowest in January and July, when air temperatures were lowest and highest, respectively. Pollen germination and tube growth in vitro were highest in spring and autumn irrespective of the cultivar. Under low night temperatures (< 15 °C), normal fruit set was not possible due to inadequate pollen production and viability, whereas the application of β-naphthoxyacetic acid to emasculated flowers enabled parthenocarpic/seedless fruit development. When pollen was not a limiting factor, both seed-containing and parthenocarpic fruit were produced. Initially, parthenocarpic fruit developed more rapidly than fruit set by pollination. However, by market maturity, both fruit types of either cultivar were similar in mean weight, size, and shape. Moreover, the external colour of seedless and seed-containing fruit was similar, whereas the percent dry matter of the seedless fruit tended to be lower. We conclude that because at times of excessively low or high temperatures pollen production and viability are adversely affected, fruit set requires assistance. In eggplant, application of the fruit-setting compound β-naphthoxyacetic acid results in the setting of seedless fruit that are similar in size and appearance to those set by natural pollination.