Diagnóstico fitossanitário da cultura do inhame (Dioscorea spp.) em áreas produtoras do Nordeste do Brasil

Abstract

The yam (Dioscorea spp.) is affected by several diseases and pests occurring in field and/or during transport and storage. It is a crop with a high social economic importance in Northeast of Brazil, showing a good expansion potential by tuber export, especially to Europe. An evaluation of disease and pest development in important producing areas was undertaken, as well as a study on the quality of tuber seed used by the growers. Visits to seven counties of Pernambuco and three of Paraíba, totaling 30 farms were done. In order to evaluate the occurrence of diseases and the damages caused by pests under field conditions, in each field five lines of 10 plants were marked, while for virus evaluation, 30 plants were randomly selected. The plants were analyzed 30 days before and at the harvest day. The nematodes were extracted by association the Jenkins method and identified by their structures under light microscope. For fungus identification, isolation and inoculation were doneand the structures were observed under light microscope. For the viruses, observation under electron microscopy, triple antibody sandwich enzyme-linked immunosorbent assay” (TAS-ELISA), with polyclonal and monoclonal antibodies specific to Yam mosaic virus (YMV), from IITA, Nigeria, and a polymerase chain reaction (PCR) with degenerated primers for detecting badnavirus and duplex reverse transcription (RT-PCR) with specific primers to YMV and Yam mild mosaic virus (YMMV) were used. The PCR and RT-PCR products were purified and sequenced in order to validate the tests used for detecting badnavirus andidentification of the potyviruses by the comparative analyses of the sequences available in the GenBank. It was observed the leaf spot caused by Curvularia eragrostidis in all areas studied, with a higher intensity on cv. Inhame-da-Costa of D. cayennensis-D. rotundata complex, whereas the damages caused by leaf wor (Pseudoplusia oo), present in all fields, were higher on cv. São Tomé of D. alata plants. The seed tubers of both yam species, collected in five farms representative of the growing areas of Pernambuco and Paraíba, after 60 days of storage, presented serious problems of green rot caused by Penicilium sclerotigenum, mealybugs (Planoccocus sp.) and tuber worms (Araecerus fasciculatus). It was identified the potyviruses YMV and YMMV, occurring in single and mixed infections with badnavirus, consisting the first detailed report with molecular information on theseviruses in Brazil.