In this analysis, we attempt to understand how monoecy and dioecy drive spatial genetic structure (SGS) in plant populations. For this purpose, plants of the genus Ficus were used as a comparative model due to their particular characteristics, including high species diversity, variation in life histories, and sexual systems. One of the main issues we assessed is whether dioecious fig tree populations are more spatially genetically structured than monoecious populations. Using the Sp statistic, which allows for quantitative comparisons among different studies, we compared the extent of SGS between monoecious and dioecious Ficus species. To broaden our conclusions we used published data on an additional 27 monoecious and dioecious plant species. Furthermore, genetic diversity analyses were performed for two monoecious Ficus species using 12 microsatellite markers in order to strengthen our conclusions about SGS. Our results show that dioecy, more than monoecy, significantly contributes to SGS in plant populations. On average, the estimate of Sp was six times higher for dioecious Ficus species than monoecious Ficus species and it was two times higher in dioecious than monoecious plant species. Considering these results, we emphasize that the long-distance pollen dispersal mechanism in monoecious Ficus species seems to be the dominant factor in determining weak spatial genetic structure, high levels of genetic diversity, and lack of inbreeding. Although Ficus constitute a model species to study SGS, a more general comparison encompassing a wider range of plants is required in order to better understand how sexual systems affect genetic structure.

Angular leaf spot is one of the major diseases of the common bean. The extensive genetic variability of this pathogen requires the constant development of new resistant cultivars. Different sources of resistance have been identified and characterized. For the State of Minas Gerais, Brazil, four main resistance sources were found: Mexico 54, AND 277, MAR 2 and Cornell 49-242. Independent characterization of these genotypes demonstrates that resistance in all four sources is dominant and monogenic. However, there are no studies on the relationship and independence of these genes. In the present work, allelism tests were carried out to understand the relationship among the resistance genes present in these four resistance sources. The data revealed a much higher complexity in the resistance inheritance of these genes than previously reported. It was demonstrated that Cornell 49-242 possesses a dominant gene (Phg-3); Mexico 54 possesses three genes, denominated Phg-2, Phg-5 and Phg-6. In MAR 2, two genes were found, one independent designated Phg-4 and the other, an allelic form of Phg-5, denominated of Phg-5 2 . Allelic forms were also found in AND 277, Phg-2 2 , Phg-3 2 and Phg-4 2 . These results have special importance for breeding programs aiming to pyramid resistance genes.

For many tree species, mating system analyses have indicated potential variations in the selfing rate and paternity correlation among fruits within individuals, among individuals within populations, among populations, and from one flowering event to another. In this study, we used eight microsatellite markers to investigate mating systems at two hierarchical levels (fruits within individuals and individuals within populations) for the insect pollinated Neotropical tree Tabebuia roseo-alba. We found that T. roseo-alba has a mixed mating system with predominantly outcrossed mating. The outcrossing rates at the population level were similar across two T. roseo-alba populations; however, the rates varied considerably among individuals within populations. The correlated paternity results at different hierarchical levels showed that there is a high probability of shared paternal parentage when comparing seeds within fruits and among fruits within plants and full-sibs occur in much higher proportion within fruits than among fruits. Significant levels of fixation index were found in both populations and biparental inbreeding is believed to be the main cause of the observed inbreeding. The number of pollen donors contributing to mating was low. Furthermore, open-pollinated seeds varied according to relatedness, including half-sibs, full-sibs, self-sibs and self-half-sibs. In both populations, the effective population size within a family (seed-tree and its offspring) was lower than expected for panmictic populations. Thus, seeds for ex situ conservation genetics, progeny tests and reforestation must be collected from a large number of seed-trees to guarantee an adequate effective population in the sample.