Late‐Acting Self‐Incompatibility and Other Breeding Systems inTabebuia(Bignoniaceae)

Abstract

Although breeding system investigations were previously performed in only nine of the 100 Tabebuia species, indications of self‐incompatibility have been found in all of them, and the four species studied for the site of incompatibility reaction showed some kind of late‐acting self‐incompatibility. Polyembryony has been found in T. chrysotricha and T. ochracea, with adventitious origin of the extra embryos being shown in the latter. We investigated the breeding system in five species of Tabebuia by hand‐pollination experiments, fluorescence microscopy study of in situ pollen tube growth, and histological analysis of postpollination events. Although both T. chrysotricha and T. heptaphylla developed fruits by self‐pollination, polyembryony was verified only in the former, which indicates that self‐fertility in Tabebuia is not necessarily associated with apomixis. The remaining species were 100% self‐sterile. Although some penetrated ovules in crossed pistils of T. vellosoi were found at the 48‐h interval, none of the ovules in selfed pistil was penetrated at the same interval, with penetration of many ovules occurring 72 h postpollination. In T. impetiginosa, ovule penetration efficiency 48 h after pollination was higher in cross‐ than in self‐pollinated pistils, and the majority of the ovules in selfed pistils were penetrated and fertilized in 72 h. The incidences of ovule fertilization and endosperm initiation were significantly slower in selfed compared with crossed pistils, and a clear developmental slowdown of the endosperm occurred in selfed pistils before abscission, although no other signs of developmental malfunctions were detected. In all of the self‐sterile species, abortion of selfed pistils occurred in a small period after pollination, and no swelling of the ovary was observed in T. umbellata. All of these results agree with the occurrence of late‐acting self‐incompatibility in T. impetiginosa, T. umbellata, and T. vellosoi, and no evidence was found that self‐sterility in these species is due to inbreeding depression.