Silício e Azospirillum brasilense associado ao controle químico sobre a severidade de Pantoea ananatis em milho

Abstract

The maize white spot (MWS) (Pantoea ananatis) is the main disease of culture, under severe conditions, significantly reduces your productivity. The use of hybrids susceptible to MWS makes it necessary to use chemicals to control the disease. Several biotic and abiotic agents are considered defensive inducers. Inducing the defences of maize plants can be an alternative in the control of the disease, aiding the chemical products. The objective of the paper was to evaluate in reducing the severity of MWS by silicon and Azospirillum brasilense, associated or not to two fungicides (picoxystrobin + ciproconazole and mancozebe) and an antibiotic (casugamycin). The experiments were divided into greenhouse, field and laboratory. In greenhouse were evaluated the effects of possible defence inducers, silicon and Azospirillum brasilense, on the reduction of MWS severity, by the inoculation of a Pantoea ananatis isolate in three susceptible maize hybrids (P1680YH, AG8780 e SUPREMO). The treatments with silicon and A. brasilense significantly reduced the severity of MWS in the hybrid P1680YH. However, in the other hybrids there was not significant difference between the treatments. The field experiment evaluated the combination of silicon, Azospirillum brasilense and chemicals in reducing severity of MWS and productivity, using hybrid P1680YH. Among the chemical treatments, the fungicide mancozebe had the lowest rate of progress and area below the disease progress curve of MWS, with reflections on crop productivity. The combinations with silicon resulted in a lower MWS severity, aiding the chemicals, resulting in a higher crop productivity. Azospirillum brasilense combined with the products did not reduce the severity of the MWS, but its effects on the physiology of the culture resulted in a higher productivity, superior to the treatments with silicon. The laboratory experiment evaluated the efficiency of the tested chemicals under the population of Pantoea ananatis colonies in petri dishes. The bacterium presented a high sensitivity to the fungicide mancozebe, a low sensitivity to the antibiotic casugamycin and was insensitive to the active ingredients cyproconazole and picoxystrobin, isolated or associated.