Avaliação de iniciadores específicos para detecção de grupos de anastomose de Rhizoctonia solani

Abstract

The genus Rhizoctonia is composed of groups of related but genetically distinct individuals grouped on the basis of molecular characteristics and a classical method of vegetative compatibility, called anastomosis groups (AGs). In this context, several specific primers based on the transcribed internal spacer (ITS) region have already been developed to discriminate AGs and their subgroups in the Rhizoctonia species complex, but there are no studies of the efficacy of these primers considering a large number of known AGs. Therefore, the objective of this work was to evaluate the efficacy of specific primers for the detection of the four predominant Rhizoctonia solani AGs worldwide (AG-1 IA, AG-1 IB, AG-2-1, AG-3 PT, AG-3 TB, AG-4 HGI e AG-4 HGII). Initially the genomic DNA of thirteen isolates of R. solani and seven of binucleated Rhizoctonia belonging to different AGs were extracted and quantified. The ITS region of the ribosomal DNA of these isolates was sequenced using universal primers (ITS1 and ITS4) to confirm the identity of the AGs. Phylogenetic relationships were analyzed by the maximum likelihood method individually. The isolates of R. solani and binucleate Rhizoctonia together with unrelated fungal species used as negative control (Fusarium oxysporum, Macrophomina phaseolina and Sclerotium rolfsii) were tested simultaneously with each set of primers described above. The identity of all AGs from R. solani and binucleated Rhizoctonia were confirmed by phylogenetic analysis of the sequences ITS region. The results of the PCR analyzes showed that all primer sets used amplified other AGs under the conditions indicated and most these primers produced amplifications for unrelated fungal species with R. solani. We conclude that the exclusive use of these primers is not indicated for the detection of AGs, since the great intra and interspecific diversity of Rhizoctonia species. Therefore, is very important to develop new specific primers based in gene regions more variables for AGs detection considering the number of AGs currently known.