Influence of repeated pollination on seed number and fruit shape of ‘Fuji’ apples

Lopsided apple fruits were found in an orchard consisting of a single commercial cultivar Fuji and pollinizers of crab-apples under conditions of natural pollination. Speculating that it was caused by inadequate partial pollination, we devised an appropriate model. We artificially pollinated one out of five pistils of apple gynoecium, and then investigated the correlations among inadequate partial pollination, seed number, distribution, and fruit shape. It was speculated that a decrease in seed number and an increase in the rate of lopsidedness were caused by inadequate partial pollination. A deviation in seed distribution was also a factor in the occurrence of lopsided fruits. Since many of the main pollinator Osmia cornifrons visited a flower repeatedly at an orchard consisting of a single cultivar and pollinizers, we analyzed the effect of repeated pollination on increasing and improving seed number in fruits and fruit shape, respectively, using artificial pollination of a pollinizer and cultivars with various S-genotypes. Repeated pollination at 24-h intervals did not contribute to fertilization, but those at 4-h intervals contributed significantly as pollen parents of seeds in fruits. The ability of pistil fertilization was maintained until four days after flowering regardless of pollination, but once fertilization occurred, this pistil was not considered to contribute to seed production 24 h after initial pollination. Those results suggested that pollinizers in full bloom be shifted more than a day seemed unnecessary at an orchard with single commercial cultivar, and repeated artificial pollination must be done within one day.