Citrus pollen tube development in cross-compatible gynoecia, self-incompatible gynoecia, and in vitro

Abstract

The route of 'Orlando' tangelo (Citrus paradisi Macf. × C. reticulata Blanco) pollen tubes was traced and compared in self-incompatible pollinations and cross-compatible pollinations with 'Dancy' tangerine (C. reticulata Blanco). In both crosses, 'Orlando' pollen germinated in the stigmatic exudate and grew between the papillae on the stigma surface and inter-cellularly between the parenchymatous cells until reaching a stylar canal by 3 days. However, in the incompatible pollination, irregular deposition of callose occurred in the pollen tube walls as early as 1 day after pollination. By day 6, pollen tubes were in the upper portion of the ovary in the compatible pollination, whereas most pollen tubes from the incompatible pollination were still in the upper style. 'Orlando' pollen tube growth rate decreased substantially by day 3 in both the self-incompatible pollination and in vitro but increased rapidly after day 3 in the compatible combination. The generative cell divided between 1 and 3 days after pollination in the compatible cross. Generative cell division was observed by day 3 in only a few pollen tubes in the incompatible cross and in cultured tubes. Compatible pollen tubes grew slowly for the first 3 days after pollination, during which time generative cells divided and then grew rapidly until fertilization. In contrast, incompatible pollen tubes showed morphological features indicative of an incompatibility reaction by 1 day after pollination and grew slowly for a period of 6 days, and then ceased growth.