Effects of Self-pollen Contamination in Artificial Pollination on Fruit Set of ‘Fuji Murasaki’ Akebia trifoliata

Abstract

Akebia trifoliata is cultivated locally in few areas of Japan. Artificial pollination is considered indispensable for stable fruit production, as Akebia spp. exhibit self-incompatibility (SI). However, little is known about the reproductive physiology required for effective artificial pollination. In this study, we investigated the effects of self-pollen contamination on the fruit set of ‘Fuji Murasaki’ (A. trifoliata), one of the main lines in Yamagata Prefecture, Japan. Both the self- and cross-pollen tubes reached the base of the ovary and penetrated the ovules at 10 days after pollination, indicating that A. trifoliata exhibits late-acting SI. Self-pollination one day before cross-pollination completely inhibited fruit set, while self-pollination one day after cross-pollination did not inhibit fruit set in both 2016 and 2020, indicating interference in cross-pollination by self-pollen contamination. Fruit set rates for artificial pollination using a 1:1 mix of self- and cross-pollen were significantly lower than those that used non-contaminated cross-pollen in both 2016 and 2019, but were comparable when using a 1:1 mix of lycopodium powder and cross-pollen. The seed number of fruit resulting from mixed pollination was not significantly lower than that of fruit resulting from cross-pollination. Interestingly, 1:1 mixed pollination of self- and cross-pollen sometimes yielded abnormal fruits with an apex that remained pale and did not soften. These results suggest that excessive self-pollen contamination in artificial pollination may not be desirable for A. trifoliata fruit production.