Genetic variability of Chrysoporthe spp. in Brazil

Abstract

Among the eight Chrysoporthe species described in the world, only Chrysoporthe cubensis and Chrysoporthe doradensis were reported in Brazil. The pathogen has as hosts several plants of the family Myrtaceae and Melastomataceae, being the genera Eucalyptus and Tibouchina, the most attacked. The fungus causes lesions in the exchange of the plants, causing the rupture of the tissues (stem and branches), reducing their growth, which can result in the death of the plant. It is believed that in Brazil there is high genetic diversity of Chrysoporthe spp. as well as possible unknown species. The objective of this work was to verify the occurrence of new Chrysoporthe species from native and non-native hosts from different regions of Brazil and to analyse the structure and genetic diversity of populations of Chrysoporthe spp. in Brazil, using microsatellite markers. For this the present study was divided into two papers, the first one was designed to study the structure and genetic diversity in the population of C. cubensis in Brazil. While the second, the objective was to study the, phylogeny, morphology, pathogenicity and population structure of a new species reported in this work. Chrysoporthe isolates were obtained from eucalyptus trees in commercial plantations and Tibouchina native tree species in forest parks and urban areas. The isolates were submitted to phylogenetic analyses using two gene regions, β-tubulin and transcribed internal space. The results of the phylogenetic and morphological analyses confirmed the existence of a new species of Chrysoporthe, which was described in this work as Chrysoporthe puriensis. Genetic diversity analyses of C. cubensis populations showed high genetic diversity in Brazil. And it was possible to verify that the isolates of C. cubensis are grouped in sub-populations according to their geographic distribution and that the highest genetic variability occurs within the sub-populations than among the sub-populations. In relation to the population analyses with the isolates of C. puriensis, the presence of a single population with very high gene and genotypic diversities were observed. The high genetic variability in C. cubensis and C. puriensis in Brazil highlights the importance of the continuity of the genetic-molecular studies of Chrysoporthe in Brazil. Possibly with more ample studies new species will be found. This reflects in breeding programs and selection of eucalyptus clones that should be careful and consider the different species and genotypes during the screenin g of the resistance of the clones to Chrysoporthe species. The results also point to the environmental importance of Chrysoporthe spp. when associated with Tibouchina species. During the study, many trees of Tibouchina spp. were found dying due to the attack of these pathogens. It is very important be performed future studies to verify how ample these pathosystems is in both native forests and in urban afforestation and reforestation. And initiate selection studies of progenies of Tibouchina spp. resistant to Chrysoporthe species.