Modern maize hybrids have greater yield potential than cultivars used in the past, particularly under stressful conditions such as high plant population and water deficit. It is possible that the yield advantage presented by modern genotypes is partially due to their better ability to resist major maize diseases. This experiment was carried out to evaluate the incidence and severity of maize leaf, stem, and ear diseases on hybrids usually grown in Southern Brazil, under different plant populations. A split plot design was used, with the main plots disposed in randomized complete blocks. Three plant populations, equivalent to 50,000, 75,000 and 100,000pl ha-1, were tested in the main plot. The hybrids Ag 12, Ag 28, Ag 303 and Ag 9012, which were cultivated expressively in the 60's, 70's, 80's and 90's, respectively, were tested in the split plot. The enhancement in plant population promoted increases on the incidence of stem diseases caused by Fusarium moniliforme, Colletotrichum graminicola e Diplodia maydis, especially on Ag 12 and Ag 28, contributing to decrease their stem standability at harvesting. The hybrid Ag 9012 had lower incidence and severity of ear diseases caused by Fusarium moniliforme e Diplodia maydis, regardless of plant population. The hybrid Ag 9012 did not express lower severity levels of leaf diseases in relation to the older hybirds used in the trial.
Zea mays; diseases; cultivars; plant densities
