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Flower emasculation is widely used in breeding programs for hybridization of fruit trees. In japanese plum (Prunus salicina), some genetic crosses made by emasculation have resulted in very low or lack of fruit set, but the causes leading to this situation are not clear. In this work, the influence of flower emasculation on fruit set was evaluated in four japanese plum-type cultivars by comparing cross-pollinations performed with and without emasculation. Fruit set and fruit drop in the crosses were characterized until harvest. To ascertain which factors in the reproductive process could be related to the lack of fruit set, compatibility was determined for each cross by the observation of pollen tube growth under the microscope and by polymerase chain reaction. Likewise, the stage of ovule development was observed under the microscope in emasculated and non-emasculated flowers. An analysis of the different pollination treatments and the study of the compatibility relationships helped to dismiss factors that intervene in the reproductive process and to identify flower emasculation as the cause of premature degeneration of ovules and its implication in determining subsequent fruit set.
Some japanese plum (Prunus salicina) cultivars are particularly prone to erratic fruit set showing very low or even null fruit set for reasons that are not clear. To ascertain the causes of lack of fruit set in some of them, different factors intervening in the reproductive process have been evaluated using flowers of three cultivars, Angeleno, Rubirosa, and Sweet August, from commercial orchards with records of very low fruit set in previous seasons and compared with a producing cultivar, Simka. Different cultivars coincident at flowering with the cultivars studied were evaluated as adequate pollenizers in each orchard. To determine which factors that intervene in the reproductive process could be related to the lack of fruit set, microscopic observations of pollen germination, pollen tube growth, pollen–pistil incompatibility, and ovule development were analyzed in flowers of different pollination treatments. Results allowed dismissal of pollen viability, pollen transfer, and pollen–pistil incompatibility as the cause of lack fruit set. However, the observation of ovule development revealed a high incidence of premature ovule degeneration on final fruit set in the three low-producing cultivars. The lack of fruit set in orchards with no apparent adverse environmental conditions is traditionally studied by analyzing the pollination process and the pollen–pistil incompatibility relationships, but the stage of development of the ovules is not usually considered. The approach used in this work may prove valuable to other species and situations of lack of fruit set, which could help to identify the causes for premature ovule degeneration.