Identificação de espécies de Badnavirus infectando bananeira no Brasil

Abstract

Virus diseases are very important in banana crops because they do not have curative control. One of the most important viruses is the banana streak, caused by several species Badnavirus, which can lead to yield losses of up to 90%. The variability found within the genus Badnavirus and the ability to fully or partially integrate its genome into the banana genome, make its diagnosis quite challenging. In Brazil, few studies have been carried out to identify the species of Badnavirus that are present in the different regions where the banana tree is grown. In this work, banana samples with suspected badnavirus infection were analyzed in order to identify Badnavirus species and also consolidate a diagnostic method that, in addition to being efficient, would be less costly for routine diagnostic tests. 35 banana samples from different Minas Gerais regions, one from Bahia and one from Tocantins were analyzed. They were first submitted to PCR diagnosis using degenerate primers and those tested positive were analyzed by RCA (rolling circle amplification) and RT-PCR to confirm the presence of the episomal form of viruses. 33 isolates from different regions of Minas Gerais, one from Tocantins and one from Bahia were analyzed. Among the 35 isolates analyzed, those that showed positive results in the three techniques had a fragment of RT/RNAse H with 540 bp amplified, sequenced and their species was identified. Among the analyzed samples, nine were negative and five positive only in PCR, showing that they were endogenous sequences of the banana. On the other hand, 21 of them were positive in the three techniques, indicating that the RCA and RT-PCR techniques were efficient for detecting the epissomal form of viruses, while the PCR indiscriminately amplified episomal and endogenous sequences. Based on the ICTV criteria that established a threshold of nucleotide identities ≥80% for equal species, five species of badnavirus already described in the literature were identified, and also one species not yet reported, the isolated MG-PHIA, which showed identities between 65 and 72% with all the species available in GenBank, not fitting into any of them. The species of Tocantins isolate was Banana streak Mysore virus (BSMyV) and the remain species with respective isolates were: isolates was Banana streak Obino l'Ewai virus (BSOLV): MG-OC, MG-CAJU; Banana streak Uganda G virus (BSUGV): MG-TERRI, MG-SEM and BA-BRP; Banana streak Uganda D virus (BSUDV): MG-CAR, MG-MA3, MG-MAR, MG-NAN, BA-WIL and MG-PRGO1 and finally, the species with the greatest number of isolates was Banana streak Uganda C virus (BSUCV): MG-CAV, MG-MA4, MG-PRCA, MG-PRGO2, MG-PR2, MG-OM, MG-WIL1 and MG-WIL2. The validation of the RT-PCR technique for the diagnosis of episomal badnavirus sequences and the identification of species present in different Brazilian fields where the banana is grown, is a relevant contribution to the Brazilian certification program to produce healthy banana seedling.