Estudo biológico e molecular de dois isolados de Lettuce mosaic virus (LMV)

Abstract

Lettuce mosaic virus (LMV), transmitted by seeds and aphids, is considered one of the most important viruses in lettuce crop, given that it causes considerable losses in the crop. Several genetic variants of LMV can occur under natural conditions, such as the strain that causes head closure in cv. Regina 579, which has been studied at the Department of Phytopathology (DFP) of the Universiadade Federal de Lavras (UFLA), denominated LMV cf. In this work, the effect of this strain over 12 lettuce cultivars was compared to that of another strain, LMV AF198, using the following cultivars: Quatro Estações, Grand Rapids, Rubete, Everglades, Salinas 88, Winslow, Colorado, Regina, Raider Plus, Balsamo, Luiza and Great Lakes. The lettuce cultivars were mechanically inoculated with the two viral isolates, maintaining a few replicates as control. The plants were visually monitored for symptom assessment and, from the 14 th day after inoculation, were weekly tested using the DAS-ELISA serological test to monitor infection development. The cultures with negative DAS-ELISA results, and those presenting different symptoms between the strains, were submitted to RNA extraction and RT-PCR. Simultaneously, specific primers were designed to amplify the P3 and 6K2 proteins. In previous studies, it has been suggested that these proteins be studied, as they are candidates for the induction of the atypical LMV cf. symptom. Among the symptoms observed, the cultivars presenting head closure when inoculated with MRL cf. were Regina 579 and Quatro Estações. In the LMV cf. strain, cvs. Rubete, Everglades, Salinas 88 and Luíza presented resistance, with negative DAS-ELISA results. The remaining cvs. Presented viral particles concentration, and were positive. In strain LMV AF198, only cvs. Everglades and Luíza maintained resistance, presenting negative result. Among the cvs. that showed positive results, Salinas 88 was highlighted given that, despite the lack of symptoms, presented viral particles concentration, with a positive DAS-ELISA result, even while resistant. When using RT-PCR, all cvs. analyzed were positive. In conclusion, there was difference between the two strains, which can be observed in the symptoms induced in cvs. and with the results obtained by DAS-ELISA and RT-PCR. The 6K2 proteins of both isolates were expressed in transgenic plants, with no differences between them, suggesting the study of the other proteins. This study provides important information on the relation between this pathogen and the host plant, and the results obtained contribute to the breeding studies of lettuce cultivars resistant to various LMV strains.