Zucchini lethal chlorosis virus (ZLCV): detecção, avaliação de danos em abobrinha de moita e reação de espécies de cucurbitáceas
José Segundo Giampan
Maria Fernandes de Jesus que tiveram força e coragem para suportar a minha dor nas horas difíceis e tanto me estimularam e animaram para dar seqüência a esse trabalho, pelo apoio, incentivo, confiança e exemplo de dignidade, DEDICO Ao meu irmão, Marcos Antônio; à minha cunhada, Jussara; aos meus sobrinhos, Junior, Mateus e Milena, e demais parentes e amigos pelo convívio, carinho, apoio em todos os momentos e, principalmente, pelas alegrias vividas, OFEREÇO SUMÁRIO RESUMO.ABSTRACT Zucchini
... l chlorosis virus (ZLCV): detection, evaluation the damage on zucchini squash and the reaction of species of cucurbits Zucchini lethal chlorosis virus is a specie of the Genus Tospovirus, transmitted by thrips (Frankliniella zucchini), which infects some species of the family Cucurbitaceae. The occurrence of this tospovirus has already been reported for several Brazilian states and its incidence in cucurbit crops has increased in the last years in some regions. Considering the importance of this tospovirus for cucurbit crops, very little is known about the damage caused by this virus and the reaction of the different species of cucurbits to infection. This work aimed: to study the efficiency of the RT-PCR for the fast and specific detection of ZLCV, to evaluate the damage caused by this virus on zucchini squash under field condition and the reaction of seven species/varieties of cucurbits to infection with this tospovirus. The detection of ZLCV by RT-PCR was studied using a pair of primers designed based on the nucleotide sequence of the S-RNA of ZLCV (AF067069). Four other tospovirus species (TSWV, TCSV, GRSV and CSNV) and other virus that infect cucurbits (mild strain PRSV-W-1, wild strain PRSV-W-C, mild strain ZYMV-M, wild strain ZYMV-Atibaia and CMV) were included in this test. The RT-PCR reaction generated a fragment of approximately 350 bp, only amplified from total RNA extracted from plant infected with ZLCV. The sequence of this fragment presented 98.2 % identity with the corresponding nucleotide sequence of the S-RNA of ZLCV deposited in the GenBank. The damage caused by ZLCV on zucchini squash (Cucurbita pepo cv. Caserta) was evaluated under field condition. Zucchini squash plants were weekly monitored for the presence of characteristic symptoms induced by ZLCV and PTA-ELISA for virus indexing. Plants were grouped based on the time the symptoms were first seen. Fruits harvested from each plant within each group were classified on marketable (M) and non-marketable (NM) based on the phenotype. Plants that did not show symptoms by the end of the crop were considered still healthy and their yield was used as control. Zucchini squash plants that showed symptoms of ZLCV infection up to 23 days after emergency (DAE) did not yield any fruit. Marketable fruits were first harvested only from plants that showed symptoms 42 DAE. However, the yield of marketable fruits was reduced by 78.5 %, as compared to that from asymptomatic plants. Plants that showed symptoms 55 DAE showed a reduction on the yield of marketable fruit of 9.6%. The reaction of seven species/varieties of cucurbits to infection with ZLCV was evaluated under field and greenhouse conditions. In the field experiment, ZLCV infection occurred naturally. In the greenhouse, plants were twice mechanically inoculated with ZLCV at the cotyledonal stage. Evaluations were based on symptoms expression and PTA-ELISA. Zucchini squash 'Caserta' and hybrid squash 'Takaiama' were highly susceptible. The cucumber 'Safira' presented low percentage of infected plants in the field and intermediate in the greenhouse. Watermelon 'Crimson Sweet', northern gherkin, long neck squash 'Menina Brasileira' and winter squash 'Alice'