Indução de resistência em milho safrinha por acibenzolar-s-metil e mananoligossacarídeo fosforilado

Abstract

In recent years farmers have gradually increased the use of chemical pesticides to mitigate the losses from diseases in corn. An alternative to reduce the use of such products may be the application of resistance inducer, taking advantage of latent genetic resistance, causing less negative impact on the environment and human health. Although, there may be an energetic expense with this induction which could hold up this form of control. With the objective of verifying the resistance induction in off-season (safrinha) corn by acibenzolar-S-methyl (ASM) and phosphorylated mannanoligosaccharide (MOS), experiments were conducted with four corn hybrids (30F90H, 30K64H, 30K73H and P4042H) in two consecutive years (2011 and 2012) in off-season environment in the municipality of Toledo - PR. In addition to the resistance inducers, a fungicide (azoxystrobin + ciproconazole) was applied, as well as water as a check. A randomized block design, with a triple factorial scheme, plus an additional treatment and three replications was used. The factors were: (A) hybrid in four levels (B) product in three levels and, (C) dose in three levels. The additional treatment was carried out with water spray, representing the level zero of the dose factor. The application of the products happened in phenological stages V8 and VT. There was observed an incidence of diverse plant pathogens in the two consecutive years, on the same hybrids, in the same location and under the same manageable conditions, probably due to diverse climatic conditions from one year to another, although hypersensitive response occurred in both years under MOS treatment. In the 2011 off-season, there was an incidence of Exserohilum turcicum, a necrotrophic pathogen, and no damaged kernels were found, while in the 2012 off-season, there was an incidence of Puccinia polysora, a biotrophic pathogen, plus significant percentage of damaged kernels. None of the applied products affected the traits plant height, ear placement, content of foliar nitrogen and percentage of damaged kernels. There was significant effect of resistance inducers on the hypersensitivity response and root lodging, without reducing the productivity compared to the water treatment. MOS increased hypersensitivity response severity and ASM reduced root lodging. The fungicide treatment (azoxystrobin + ciproconazole) showed better control of foliar diseases (P. polysora and E. turcicum) and higher yield in both years, and in 2011 it reduced stalk lodging and increased the mass of thousand kernels