Seasonal Changes in the Self-Incompatibility and Pollen Tube Growth in Japanese Pears (Pyrus serotina Rehd.)

Abstract

In order to investigate the self-incompatibility reaction in the Japanese pear (Pyrus serotina Rehd.), fruit setting was examined in the trees blooming at 12 different times within a year from February to September by selfing and crossing the flowers at bud and full bloomed stages. When self-pollinated in full bloom, there was little or no fruit set at all the flowering times, suggesting the presence of strong self-incompatibility in the flowers. When self-pollinated at the bud stages, about 10% of the total flowers pollinated were set throughout the season, indicating weak incompatibility.
Pollen tube protrusion from the excised-styles cultured on agar media was also studied. At all flowering times, the percentage of mature styles protruding pollen tubes when cross-pollinated was higher than that when selfed, except in the styles obtained on January 20, soon after rest. The number of immature styles in the floral buds with pollen tubes was similar regardless of whether were self or cross-pollination performed. These results may indicate that the pollen tubes passed through immature styles more easily than did through mature one, even though self-pollination had taken place.
The length of styles in the floral bud which was capable of setting fruit was about one half that of styles in the opened flowers. This fact support the possibility that the physical length of styles in the flowers might be one of the factors responsible for a breakdown of self-incompatibility after bud self-pollination in P. serotina.