Gênero Calonectria: resistência genética esequenciamento de genomas de diferentes espécies

Abstract

Eucalyptus is one of the most widely cultivated plant genera in the world. It is estimated that the area planted with Eucalyptus spp. exceeds 20 million hectares established, mainly due to the great diversity of these species, suitability for different climates and soils, rapid growth rates and use for multiple products such as wood, cellulose, fodder, biofuels, essential oil and bioactive chemicals. The productivity of these plantations can be limited by the occurrence of some phytopathogens, since the main areas planted commercially in Brazil are in humid and hot locations, with an ideal climate for the emergence of fungal diseases, such as leaf spot and defoliation caused by Calonectria spp. one of the most important diseases of eucalyptus in tropical regions. Currently, 45 species of Calonectria occur in Brazil, 14 of which are associated with eucalyptus, with the C. pteridis species being the most prevalent in the field in the states of Pará and Maranhão. The pathogen causes intense defoliation of plants during rainy periods, drastically reducing crown depth. This disease can be controlled by planting resistant genotypes. The aim of this study was therefore to evaluate the level of resistance of 380 Eucalyptus spp. clones to defoliation and leaf spot caused by Calonectria spp. using multivariate statistical techniques for selection and evaluation. In the first experiment, two different hierarchical methods were used: Unweighted Pair-Group Method Using Arithmetic Averages (UPGMA) and Tocher Optimization for selecting the clones. The Tocher optimization method based on Mahalanobis distance was consistent in separating the clones, corroborating the results obtained by principal component analysis. On the other hand, the UPGMA method made it possible to distinguish between resistant and susceptible species.The resistant species (R) are E. urophylla x E. camaldulensis; E. urophylla x (E. grandis x E.urophylla); E. grandis x E. brassiana; E. grandis x Eucalyptus spp. and E. grandis x E.pellita. It is therefore recommended that further studies be carried out in areas with different soil and climate conditions from the region studied here, to determine whether the clones considered resistant in this study are the ones recommended for other regions where the disease occurs. The second experiment aimed to sequence three complete genomes of Calonectria species found in Brazil, to facilitate future research into taxonomy, population genetics/diversity and genes associated with pathogenicity. Sequencing was carried out using a standard library on the Ilumina platform, the raw data was prepared in the Spades software and the data processing (filtering and assembly) in Geneious Prime. To validate the identity of the sequenced isolates, the Act, cmdA, His, rpb2, Tub and EF1-α gene regions were extracted from the assembly and a maximum likelihood phylogeny was constructed using the reference sequences. The availability of the genomes allows comparative and population genomics studies to be carried out within the species complex and will also promote future studies on genes related to the pathogenicity, adaptability and mating of these important phytopathogens.