Outcrossing Rate and Stigmatic Receptivity in Cherimoya (Annona cherimola Mill., Annonaceae), a Dichogamous Subtropical Fruit Tree Species

Cherimoya (Annona cherimola Mill) belongs to the Annonaceae, a basal Angiosperm family that includes a number of tropical and subtropical fruit tree species. Cherimoya shows protogynous dichogamy, a common characteristic in Annonaceae, where female and male structures do not mature simultaneously. Moreover, flowers of the same genotype usually open synchronously and, consequently, transfer of pollen between different flowers of the same genotype is difficult. This mechanism has been assumed to prevent self-fertilization and to encourage cross-pollination and has clear implications both from a plant breeding perspective and in an agronomic context. Inadequate pollination is one of the most important factors that limit commercial production of cherimoya resulting in low fruit set and in the production of misshapen fruits. This is due to the lack of overlap between the male and female stages and the expansion of the crop to areas outside its native range in absence of its natural pollinating insects. As a consequence, hand pollination is a common practice for commercial production. In spite of the implications of this isolating mechanism, its efficiency has not been previously evaluated. In this work, we evaluate stigmatic receptivity under the microscope and natural outcrossing rate using molecular markers to test the paternity of the seeds. The results obtained show that stigmas can still be receptive when the flowers pass to the male stage and that a surprisingly high proportion of the seeds produced are the result of self-fertilization. The results are discussed in terms of the implications of these results both in plant breeding and in an adequate crop handling.