Pollination and parthenocarpy in the production of Bartlett pears in California

CALIFORNIA has over 37,000 acres of Bartletts. Experiment station workers in the state have since 1918 recommended interplanting pollinizers for this variety. In spite of this, most of the Bartlett orchards are now in solid blocks. Pollinizing varieties have been grafted over, and new plantings are almost invariably solidly to Bartletts. Only a few Bartlett growers make any effort to provide honey bees during the blossoming period. The question arises, therefore, as to what accounts for the high yields of a self-sterile variety planted in solid blocks. This report covers a five-year study and shows that the Bartlett pear, though nearly self-sterile, is self-fruitful in most California orchards because of the production of parthenocarpic fruit. Vegetative parthenocarpy was responsible for most of the seedless fruit produced. Stimulative parthenocarpy due to self-pollination did not give significantly greater fruit sets than those effected by vegetative parthenocarpy alone. Parthenocarpy means development of the edible fruit without fertilization. Parthenocarpic fruits are seedless. They have been divided into two types—vegetative and stimulative. Vegetative parthenocarpy implies that the fruit developed without pollination, while stimulative parthenocarpy indicates that they developed as a result of the stimulus of pollination.