DIVERSIDADE GENÉTICA DE POPULAÇÕES DE TOMATO CHLOROSIS VIRUS EM TOMATEIRO BASEADO NO GENE DA PROTEÍNA P22

Abstract

Tomato chlorosis virus (ToCV) (Crinivirus genus, Closteroviridae family) is considered an important pathogen for tomato production and has been reported in many countries, including Brazil. ToCV has a bipartite genome, consisting of two simple tapes RNA molecules of positive-sense, separately encapsidated in an elongated and flexuous particle. ToCV is naturally transmitted by some whitefly species. Infected tomato plants display characteristic symptoms of internerval chlorosis, vigor reduction, and consequently productivity decrease. However, little is known about the population structure of this virus in the country. Considering the species’ importance as a problem to tomato production chain, this study aimed to investigate the genetic structure of ToCV population on the basis of the complete ORF2 sequence, which encodes the p22 protein, described as a gene silencing suppressor. The study was based on the sequences of isolates obtained from Solanum lycopersicum (tomato) samples collected in 2015 and 2016 in the states of Goiás (GO), Paraná (PR), and Rio de Janeiro (RJ), Brazil. Twenty-eight clones were obtained and their nucleotide sequences were analyzed together with other sequences obtained from GenBank. The nucleotide sequences of isolates from Brazil were compared to South Korean (KOR) and Spanish (ESP) isolates. Results confirm the subdivision of ToCV population into two groups on the basis of nucleotide sequence of p22 gene, denominated Type I (only Spanish isolates), and Type II (isolates from Spain and other countries). The main indicators of genetic variability presented relatively low values, but with genetic differentiation among the populations, in relation to Brazilian isolates, and they are genetically closest to South Korean than to Spanish isolates. Phylogenetic analysis shows that the Brazilian isolates form a monophyletic group with evident genetic structure of subpopulations on the basis of geographic origin. Mutation seems to be the main mechanism of genetic variability among the analyzed isolates, and a negative or purifying selection may be acting to maintain the amino acid sequence of p22.