Orientador: Marcelo Agenor Pavan / Banca: Rumy Goto / Banca: Norberto da Silva / Banca: Alexandre de Moura Guimarães / Banca: Eliezer Rodrigues de Souto / Resumo: O trabalho teve como objetivos avaliar diversas progenies de alface da geracao [(Brasil 303 x Tinto) Elisa] F5 RC1, previamente selecionadas para tolerancia a "Lettuce mosaic virus" - (LMV-II), "Lettuce mottle virus" (LeMoV) e Tospovirus e o efeito de diferentes praticas culturais no controle de fitovirus na cultura da alface, em duas epocas do ano (outono/inverno e primavera/verao). Os fatores avaliados foram: cobertura do solo (palha de arroz e sem cobertura), cultivo protegido (tunel coberto com filme PEBD aditivado antivirus de 150 æm e tunel coberto com tela anti-afideo) e 18 progenies, avaliando os seguintes aspectos agronomicos: area de projecao da copa, massa fresca da parte aerea da planta, produtividade, fechamento de "cabeça", tempo de inicio do pendoamento e incidencia de fitoviroses. A avaliacao da incidencia de fitovirus na cultura foi realizada atraves de observacao visual dos sintomas, sendo que amostras de plantas que apresentavam sintomas foram coletadas e examinadas atraves de testes moleculares de diagnose especificos para LMV-II, LMV-IV, LeMoV e Tospovirus. Para algumas amostras sintomaticas negativas ainda foram realizados testes de RT-PCR para possivel deteccao de "Cucumber mosaic virus". (CMV), testes de inoculacao mecanica em hospedeiras diferenciadoras e analises de microscopia eletronica. Quanto aos aspectos agronomicos das progenies, observou-se que o tratamento "palha de arroz"apresentou resultado superior aos demais tratamentos para as caracteristicas massa fresca e produtividade e igual desempenho ao tratamento "solo nu" para as caracteristicas fechamento de "cabeça" e tempo de inicio de pendoamento. Dentre as 2 progenies testadas, se destacaram as de numero 6 e 7 por apresentarem maior tolerancia a viroses e caracteristicas agronomicas equivalentes a cultivar comercial utilizada como controle. Na avaliacao visual de fitoviroses... / Abstract: The research aimed to evaluate various progenies, obtained from the crossing of [(Brasil 303 x Tinto) Elisa] F5 RC1, previously selected for tolerance to "Lettuce mosaic virus" - (LMV-II), "Lettuce mottle virus" (LeMoV) and tospovirus and the effect of different phytovirus control practices in lettuce, in two periods of the year (autumn/winter and spring/summer). The factors evaluated were: soil covering (straw of rice and bare soil); protected development with a tunnel covered with an anti-virus PEBD treated film of 150 ìm and a tunnel covered with anti-aphid screen; and 18 progenies, evaluating the following agronomic aspects: area of top projection, fresh mass of the aerial part of the plant, productivity, closing of "head" and time at the beginning of tasselling and incidence of phytovirosis. The evaluation of phytovirus incidence in the crop was accomplished through visual observation of symptoms. Samples of plants showing symptoms were collected and taken to the laboratory for molecular tests to specifically detect LMV-II, LMV-IV, LeMoV and tospovirus. For some negative symptomatic samples, tests of RT-PCR were accomplished to detect possible infection by "Cucumber mosaic virus"- (CMV), and mechanical inoculation tests in differential plant, and electronic microscopic analysis. As for the agronomic aspects of the progenies, it was observed that the "rice straw" treatment presented better results than other the treatments for the fresh mass and productivity parameters, and equal performance on the "bare soil" treatment for the parameters closing of "head" and time at the beginning of tasseling. Among the tested progenies, number 6 and 7 were distinguished for presenting better tolerance to phytovirosis and agronomic characteristics equivalent to the commercial cultivar used as control. In the visual evaluation of phytovirosis, it was verified that 3,65%... / Doutor