Prevalência de espécies de orthotospovirus infectando tomateiros portadores do gene >i<Sw>/i<-5 e efeito do crinivirus >i<Tomato chlorosis virus>/i< na infecção com orthotospovirus

Abstract

Prevalence of orthotospovirus infecting Sw-5 carrying tomato hybrids and the effect of the crinivirus Tomato chlorosis virus on the infection of orthotospovirusThe spotted wilt complex is one of the most important virus diseases in tomatoes, consisting in Brazil of four species belonging to the genus Orthotospovirus, designated as Tomato spotted wilt virus (TSWV), Tomato chlorotic spot virus (TCSV), Groundnut ringspot virus (GRSV), and Chrysanthemum stem necrosis virus (CSNV). Transmission occurs in a persistent-propagative manner by thrips. This pathosystem is an example of a polycyclic disease in which the primary inoculum has a continuous and dynamic role, and where virus transmitting insects and alternative hosts play a key function, requiring a more complex area-wide disease management. To overcome such singularity, genetic resistance is the foundation stone for a sustainable management in commercial fields, providing a broad-spectrum resistance to the orthotospovirus species in Brazil. However, spotted wilt symptoms on resistant varieties carrying the resistance gene Sw-5 are more and more frequent in the field. The aim of this work was to study the prevalence of the different species of orthotospovirus in commercial fields of fresh-market tomatoes from surveys on delimited plots of a thousand plants in a number of tomato growing regions. Additionally, the coinfection with the crinivirus ToCV was studied. The incidence of orthotospovirus-like symptoms on Sw-5 resistant varieties in 2017/ 2018 was low, ranging from 0.1 to 3.6%. 71.5% of the symptomatic samples were orthotospovirus positive. Nucleotide sequencing of selected positive isolates resulted in 70.5% of the isolates identified as GRSV and 29.5% as TCSV after alignment of the L and S RNA segments in GenBank. For the M RNA segment, all the isolates showed identity to the GenBank orthotospovirus reassortant accession HQ644141.1. The other two orthotospovirus reported in Brazil -CSNV e TSWV -were not detected. Positive coinfection with crinivirus ToCV corresponded to a low 5.0 % incidence, lacking conclusive results that could support the relation of the incidence of the crinivirus to the occurrence of orthotospovirus on Sw-5 resistant varieties, showing, however, that the susceptibility to the GRSV or to the TCSV of the Sw-5 carrying varieties is not related to coinfection with ToCV. When mechanically transmitted, GRSV e TCSV originated from Sw-5 resistant varieties in the field revealed incidence of infected plants similar in both homozygous and heterozygous varieties, as well as the nonresistant check, suggesting that the Sw5/ Sw5 homozygous condition is not an advantage.