Grupos de anastomose de Rhizoctonia: diversidade em brássicas e tomate no Brasil e utilidade do gene RPB2 para análise filogenética

Abstract

Rhizoctoniosis, a disease caused by fungi of the genus Rhizoctonia, is one of the main factors that limits the development of vegetables, such as brassica and tomato. The most important criterion for delineating Rhizoctonia species is differentiation by anastomosis groups (AGs). The knowledge of anastomosis groups and subgroups is of great importance for understanding the ecology and genetic diversity of the pathogen and its possible implications for disease control measures. Among the Rhizoctonia AGs identification techniques, the study of the ITS-rDNA region is the most used, however, more conserved gene regions, encoding proteins, should also be considered. The present study aimed: (i) to identify Rhizoctonia anastomosis groups associated with brassica and tomato species in Brazil, and (ii) evaluate the usefulness of the RPB2 gene for phylogeny and identification of Rhizoctonia anastomosis groups. One hundred and twelve Rhizoctonia isolates obtained from vegetable brassicas and tomato in eight Brazilian states were used. Based on phylogenetic analyses of the ITS region, the isolates were separated into seven anastomosis groups; three of R. solani (AG-1-IB, AG-2-2IIIB and AG-4-HGI) and four of binucleate Rhizoctonia (AG-A, AG-F, AG-G and AG-R). AG-4-HGI was the most prevalent, present in all Brazilian states surveyed. This was the first report of the occurrence of AG-F associated with tomatoes and AG-4-HGI, AG-2-2IIIB, AG-A, AG-G and AG-R associated with brassica plants in Brazil. In a second step, 40 isolates of R. solani and binucleate Rhizoctonia belonging to different anastomosis groups were identified through sequencing and phylogenetic reconstruction of the RPB2 gene. The results of the phylogenetic analyses corroborate previous studies and confirm the identity of most of the isolates. The RPB2 region allowed to separate the Rhizoctonia anastomosis groups into distinct clades with high posterior probability values. The present study revealed that the RPB2 gene has great potential for phylogenetic studies of Rhizoctonia anastomosis groups, and can be used as an alternative marker to the ITS region.