Vegetative parthenocarpy in the cactus pear Opuntia ficus-indica (L.) Mill

The dependence of fruit development on fertilization was studied in two clones of Opuntia ficus-indica, Ofer and BS1. Fruits of the done Ofer bear fully developed seeds, whereas fruits of the clone BS1 contain only degenerated seeds and it was suspected that BS1 is parthenocarpic. The two clones differed in their pattern of fruit development. The increase in fruit fresh weight in Ofer was a result of both peel and pulp growth, whereas in BS1 fruit growth was mainly due to pulp growth and the peel had reached its final weight almost at anthesis. Pulp growth in BS1 commenced earlier and was faster than in Ofer, but the final pulp weight in BS1 was only 64% of that in Ofer. Seed growth in BS1 was limited to the development of semilignified and lignified seed coats, whereas in Ofer 43'5% of the seeds were completely developed, the remainder being similar to those found in BS1. Fruits bearing well-developed seeds were also found in a ‘mutant’ of BS1 that, like Ofer, contained smaller ovules at anthesis than flowers of the regular BS1 genotype. Germination in vivo and in vitro were similar in BS1 and Ofer, but pollen tubes failed to reach the ovules in the regular BS1 genotype, while penetrating the ovules in Ofer and the small-ovuled genotype of BS1. Good-quality fruits similar to Ofer fruits in weight but with a higher peel to pulp ratio developed in BS1 after flower- sterilization in the spring and in the autumn. In Ofer, sterilized flowers failed to develop fruits in spring and partially set fruit in the autumn; the fruits consisted almost exclusively of peel tissue. It was concluded that BSÎ is a vegetative parthenocarpic clone, i.e., that pollination is not required for fruit set and development.