In recent years, mosaic became one of the most important diseases affecting maize (Zea mays) crops. It is caused by a potyvirus complex transmitted by aphid species. The aim of this work was to identify factors that may contribute to increase the incidence and dissemination of this disease. Seedlings of 115 cultivars from three different National Maize Cultivars Trials were tested for their susceptibility to the virus complex via mechanical inoculation of five plants of each cultivar, between October/97 and February/98. Most cultivars were susceptible and showed mosaic symptoms 15 days after inoculation. Several graminaceous species were also inoculated and showed to be hosts of the potyvirus complex. Using the dot-ELISA test, the virus complex could be detected in maize plants collected from different regions of São Paulo, Minas Gerais and Goias states. Between March/97 and February/98 two maize inbred lines were planted monthly and incidence of mosaic was evaluated weekly. The highest incidence was observed in the summer, coinciding with the increase of temperature and the levels of rainfall. These results may contribute to recommending control measures.
