Identificação sorológica e molecular de vírus em espécies de Cucurbitáceas em áreas produtoras do Tocantins e seus efeitos em diferentes hospedeiros

Abstract

Cucurbit crops may be affected by several virus diseases, which might cause up to 100% of yield losses. Plants infected with viruses show mosaic, leaf reduction and deformation in leaves and fruits, and the symptoms depend on the infected hosts, becoming more severe with the occurrence of mixed infections. Due to its environmental conditions, favorable to the emergence of viruses, the state of Tocantins has shown a high incidence of virus diseases in the field. However, no studies aimed at identifying and characterizing those diseases have been carried out, making it difficult to develop breeding programs approaching disease resistance in pumpkins. Therefore, the main objective of this study was to identify and characterize, serological and molecularly, the pumpkin and watermelon virus isolates collected in the state of Tocantins, in collaboration with researchers from the University of Tocantins (UFT). The identification of those isolates will be relevant to support and improve UFT breeding programs, and establish control measures for virus diseases of cucurbit crops in the field. Twenty five samples were collected from cucurbit plants showing characteristic symptoms of viruses in different regions of Tocantins. Those isolates were inoculated in different species: zucchini squash (Cucurbita pepo cv. 'Caserta'), trailing pumpkin (C. moschata ´Menina Rajada´), watermelon (Citrullus lanatus' Crimson Sweet'), melon (Cucumis melo), papaya (Carica papaya), cucumber (Cucumis sativus), Chenopodium amaranticolor and Chenopodium quinoa for biological identification. In addition, DAS-ELISA, using specific antisera and RT-PCR were carried out for virus diagnosis. Genomic fragments, from coat protein region, were amplified, sequenced and analyzed. Fourteen, or 56%, of the 25 isolates studied, were identified as Squash mosaic virus (SqMV). Seven of them were detected in Caserta squash and another seven in watermelon. The remaining isolates were identified as Zucchini yellow mosaic virus (ZYMV). Contrary to what occurs in other Brazilian regions, SqMV presented the higher incidence in the analyzed samples. When SqMV isolates infected watermelon plants, they caused mosaic and leaf distortion, unlike what has been described by several authors in other parts of Brazil. The coat protein nucleotide analysis of the 14 SqMV isolates showed an identity among them that varied from 86% to 100%, and the identity between them and the isolates of the GenBank was from 86% to 88%. The aminoacid analysis of the same region showed an identity from 95% to 100%. The identity between them and the isolates of the GenBank varied from 91% to 97%. The virus isolate that presented the higher variability was the one from Porto Nacional, named PN2. The coat protein fragment of ZYMV analyzed, showed an aminoacid identity of 100% among the Brazilian isolates and also among the virus isolates from the GenBank. It showed that this region is highly conserved, therefore inappropriate for variability and phylogeny analysis.