-(Polyembryony and aspects of embryogenesis in Tabebuia ochracea (Chamisso) Standley (Bignoniaceae)). The origin of the extranumerary embryos and the embryogeny of Tabebuia ochracea were analysed. Extranumerary apomictic embryos are of adventitious origin from hypostase cells and from the integument of ovule micropilar region. The embryogeny corresponds to Onagrad type. Among 233 dissected seeds, 81.37% presented polyembryony and up to seven embryos were detected in a single seed. Sexual and adventitious embryos can develop together in a single seed. Some of the adventitious embryos show severe morphoanatomical anomalies that can affect their development into seedlings.Key words -apomixis, Bignoniaceae, polyembryony, Tabebuia ochracea RESUMO -(Poliembrionia e aspectos da embriogênese em Tabebuia ochracea (Chamisso) Standley (Bignoniaceae)). A origem dos embriões supranumerários e a embriogenia de Tabebuia ochracea foram analisadas. Embriões supranumerários apomíticos têm origem adventícia a partir de células da hipóstase e do tegumento da região micropilar do óvulo. A embriogenia corresponde ao tipo Onagrado. Das 233 sementes dissecadas 81,37% apresentaram poliembrionia e foram encontrados até sete embriões em uma mesma semente. Aparentemente, embriões sexuais e adventícios podem se desenvolver juntos, numa mesma semente. Alguns dos embriões adventícios apresentam alterações morfoanatômicas graves que podem prejudicar seu desenvolvimento em plântulas.

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Apomixis and polyploidy have been important in the evolution of the angiosperms, and sporophytic apomixis has been associated with polyembryony and polyploidy in tropical floras. We studied the occurrence of polyembryony in populations of tetraploid Anemopaegma acutifolium, A. arvense and A. glaucum from the Brazilian cerrados, and histological features of sexual and apomictic processes were investigated in A. acutifolium. All populations and species were polyembryonic (68.9-98.4% of seeds). Normal double fertilization occurred in most ovules, with exceptions being that 3% of ovules were penetrated but not fertilized and in 4% of ovules both synergids were penetrated. The penetration of both synergids suggests a continuous attraction of pollen tubes and polyspermy. Adventitious embryo precursor cells (AEPs) arose from nucellar and integumental cells of the ovule in pollinated and unpollinated A. acutifolium, indicating sporophytic apomixis. However, further embryo and endosperm development required pollination and fertilization. This pseudogamy also allows concurrent sexual embryo development. Similar polyembryony rates and polyploidy indicated that A. arvense and A. glaucum are also apomictic, forming an agamic complex similar to that observed for some species of confamilial, but not closely related Handroanthus. The co-occurrence of apomixis and polyploidy in different groups of Bignoniaceae indicates homoplasious origin of these agamic complexes.

Self-compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post-pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self- and cross-pollinated pistils. We found that the species is self-fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late-acting self-incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis-related pseudo-self-compatibility, as in other self-fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit-set and persistence ability in fast-changing tropical habitats.

Since tropical trees often have long generation times and relatively small reproductive populations, breeding systems and genetic variation are important for population viability and have consequences for conservation. Miconia albicans is an obligate, diplosporous, apomictic species widespread in the Brazilian Cerrado, the savanna areas in central Brazil and elsewhere in the Neotropics. The genetic variability would be, theoretically, low within these male-sterile and possibly clonal populations, although some variation would be expected due to recombination during restitutional meiosis. We used ISSR markers to assess genetic diversity of M. albicans and to compare with other tropical trees, including invasive species of Melastomataceae. A total of 120 individuals from six populations were analysed using ten ISSR primers, which produced 153 fully reproducible fragments. The populations of M. albicans presented mean Shannon's information index (I) of 0.244 and expected heterozygosity (H ) of 0.168. Only two pairs of apparently clonal trees were identified, and genetic diversity was relatively high. A hierarchical amova for all ISSR datasets showed that 74% of the variance was found among populations, while only 26% of the variance was found within populations of this species. Multivariate and Bayesian analyses indicated marked separation between the studied populations. The genetic diversity generated by restitutional meiosis, polyploidy and possibly other genome changes may explain the morpho-physiological plasticity and the ability of these plants to differentiate and occupy such a wide territory and different environmental conditions. Producing enormous amounts of bird-dispersed fruits, M. albicans possess weedy potential that may rival other Melastomataceae alien invaders.

Polyploidization is common among angiosperms and might induce typically allogamous plants to become autogamous (self-compatible, relying on sexual self-fertilization) or apomictic (achieving asexual reproduction through seeds). This work aimed to determine whether neopolyploidy leads to the breakdown of the self-incompatibility system in the hexaploid non-apomictic species Handroanthus serratifolius (Vahl) S. Grose, through analyses of its floral biology, pollination biology and breeding system. Although anthesis lasted for three days, increasing the overall floral display, receptivity decreased as of the second day. Centridini and Euglossini bees were the main pollinators, and low nectar availability (1.95 ± 1.91 μl/flower) might have obliged them to visit multiple flowers. We observed low reproductive efficacy. That might be explained by self-sterility and by the great number of flowers per individual, which could increase the frequency of geitonogamy. Ovule penetration by the pollen tubes in self-pollinated pistils with posterior abscission indicated late-acting self-incompatibility in H. serratifolius, as observed in other diploid Bignoniaceae species, although inbreeding depression cannot be excluded. The self-sterility found in the monoembryonic, hexaploid individuals studied here contrasts with the results for other neopolyploid Handroanthus and Anemopaegma species, which are often autogamous and apomictic. Our results suggest that neopolyploidy is not the main factor leading to self-fertility in Handroanthus.Key words: apomixis, late-acting self-incompatibility, monoembryony, polyploidy, Tabebuia serratifolia Acta Botanica Brasilica 27(4): 714-722. 2013. Self-sterility in the hexaploid Handroanthus serratifolius(Bignoniaceae), the national flower of Brazil

The tropical Bignoniaceae is mostly late-acting self-incompatible (LSI) and depends on a guild of medium to large sized bees for their pollination. Adenocalymma nodosum and A. peregrinum are syntopic shrubs in savanna areas with similar flowers and flowering overlap. In this sense, the aims of the present study were to analyse the pollination biology and breeding systems of these species, and to check for bilateral compatibility which could hinder reproductive isolation and species boundaries. Flower features such as yellow corolla, sweet scent and diurnal one-day anthesis were similar between species. However, they differed in nectar production patterns, which showed higher volume in A. nodosum and was irregular in A. peregrinum. The main pollinators for both species were medium to large Centridini bees. Many nectar and pollen robbers may disturb effective pollination and help to explain the low natural fruit-set. The species were self-sterile but pollen tube growth down to the ovules and differential ovary development indicated LSI, as in most Bignoniaceae studied to date, which reinforce the idea of family clustering for this self-incompatibility system. Fruit-set from interspecific hand pollinations was similar to those of intraspecific cross-pollinations, with high seed viability (88%) and seedling development. Similar floral biology and guild of pollinators, and bilateral inter-compatibility indicate that natural hybridization is possible among these species.

Neopolyploidy has been associated with gametophytic apomixis and breakdown of gametophytic self-incompatibility. Nevertheless, Bignoniaceae presents agamic polyploid complexes with neopolyploidy associated to sporophytic apomixis. Apomictic populations are commonly polyploid, polyembryonic and self-fertile, while diploids are mostly late-acting self-incompatible (LSI) and monoembryonic. Contrastingly, Handroanthus serratifolius shows hexaploid monoembryonic and polyembryonic populations, although breeding system has been studied only for monoembryonic individuals, which are LSI. Our aim here was to investigate breeding system and early embryology in polyembryonic individuals of H. serratifolius to define if they form an agamic polyploid complex. Experimental pollinations and histological analyzes of ovules and young seeds were carried out. Megasporogenesis and megagametogenesis occurred as in other sexual species of Bignoniaceae. The polyembryonic individuals were self-fertile and double fertilization was observed both after self and cross-pollinated pistils. Adventitious embryos originated from the hypostasis and integument of the ovule, indicating sporophytic apomixis. Adventitious embryo precursor cells occurred in all pistils, including unpollinated ones. But unpollinated pistils aborted possibly due to absence of endosperm, and pollination was required for fruit-set (pseudogamy). It is possible that the self-fertility in polyembryonic individuals ensues as the initial endosperm of self-fertilized ovules supply early adventitious embryos development, and these embryos would later prevent the abortion of selfed pistils. The sporophytic apomixis in polyembryonic populations and the occurrence of sexual monoembryonic populations of H. serratifolius allows us to consider the species part of an agamic polyploid complex. But in contrast with other Handroanthus agamic complexes, both apomictic and sexual LSI plants were hexaploid.