Populações hexaplóides e apomíticas de Handroanthus Serratifolius (Vahl.) S. Grose (Bignoniaceae) com diferentes sistemas reprodutivos

Abstract

Among the polyploid species of Bignoniaceae investigated so far, only Handroanthus serratifolius shows self-sterility. Handroanthus serratifolius is hexaploid, and presents monoembryonic and self-sterile populations, as well polyembrionic populations with unknown breeding system. The objective of this study was to determine if the polyembryonic populations of H. serratifolius were sporophytic apomictic and consequently self-fertile, and verify that the monoembryonic population showed late-acting self-incompatibility system (LSI), confirming the idea that polyploidy does not result in self-fertility. Experimental pollination and histological analyzes of ovules and young seed after pollination treatments were carried out. Polyembryonic individuals produced reduced megagametophyites of the Polygonum type. These plants were self-fertilite and showed adventitious embryos precursor cells (PEAs), which differentiated from the hypostasis and from the integument at the micropylar region of the ovule, indicating the presence of sporophytic apomixis and corroborating the finds for other polyploid and polyembrionic species of the family. The self-fertility seems to be related to the expression of sporophytic apomixis and not polyploidy, because the hexaploid and monoembryonic individuals investigated are self-sterile. Histological analyses of post-pollination events in monoembryonic individuals showed no malformation neither in the zygote nor in the endosperm of self-pollinated pistils. Endosperms in these selfed pistils were not different from endosperms in later stages of development in cross-pollinated pistils, indicating that self-pollinated pistils abortion is due to LSI action, as observed in other species investigated so far. The presence of PEA arising from the hypostasis was also observed in self-fertile and monoembryonic individuals, indicating that these individuals have the potential for expression of sporophytic apomixis. Our results suggest that polyploidy seems to be responsible for the expression of sporophytic apomixes. However, polyploidy does not seem to have any direct relationship with self-fertility found in polyembryonic populations, but the presence and development of adventitious embryos seem to be the stimulus for the maintenance of self-pollinated pistils in H. serratifolius.