Species of Calonectria associated with Eucalyptus plantations in northeastern Brazil

Abstract

In recent decades, commercial Eucalyptus plantations have expanded toward the warm and humid regions of northern and northeastern Brazil, where Calonectria leaf blight (CLB) has become the primary fungal leaf disease of this crop. CLB can be caused by different Calonectria species, and previous studies have indicated that Calonectria might have high species diversity in Brazil. Therefore, this study aimed: 1) to characterize the species of Calonectria associated with Eucalyptus plantations in the Pará and Maranhão states, trough morphological and phylogenetic analyses and to confirm their pathogenicity to Eucalyptus, (2) to determine the genotypic diversity within each Calonectria species, (3) to understand the mating strategy of each Calonectria species and, (4) to determine the species diversity of Calonectria and its distribution in different Eucalyptus plantations. During disease surveys conducted between 2020 and 2021 in commercial plantations of Eucalyptus in northeastern Brazil, diseased leaves from Eucalyptus trees and soil samples were collected, and 206 Calonectria isolates were obtained. A total of eight species of Calonectria were find in association with Eucalyptus plantations, of which two were new to science, C. paragominensis sp. nov. and C. imperata sp. nov. Also, was the first report of C. quinqueramosa and C. amazonica causing leaf blight on E. urophylla trees in northeastern Brazil. The complete species collection was C. imperata with 48.7% of all the isolates, followed by C. amazonica (24.9%), C. ovata (9.1%), C. brasiliensis (6.1%), C. variabilis (4.1%), C. quinqueramosa (3.6%), C. paragominensis (2%), and C. maranhensis (1.5%). The pathogenicity of C. paragominensis, C. imperata and C. quinqueramosa to Eucalyptus was confirmed by fulfilling the Koch’s postulates. Concerning to genetic diversity, C. imperata presented the highest genetic diversity, with 17 genotypes in 96 isolates, followed by C. brasiliensis with 10 genotypes in 12 isolates. Regarding the mating system, MAT1-1-1 and MAT1-2-1 genes amplification showed that C. maranhensis is putative heterothallic, and that the asexual cycle is the main reproductive mode of C. amazonica. The most prevalent species were C. amazonica and C. imperata, found in seven and six plantations, respectively. Our understanding of the species, genetic diversity, distribution, mating strategy, and morphological characteristics of Calonectria in ten commercial Eucalyptus plantations in northeastern Brazil has increased as a result of this study. This knowledge could be used to create an effective management strategy for CLB in Eucalyptus plantations and the breeding of resistant Eucalyptus clones.