DOENÇAS FOLIARES E PODRIDÃO DE GRÃOS COM USO DE FUNGICIDA EM HIBRIDOS DE MILHO E ASSOCIAÇÃO À EXPRESSÃO DE ENZIMAS NO GRÃO EM DIFERENTES ESPAÇAMENTOS

Abstract

The objective of this study was to evaluate the effect of fungicide application on the incidence of foliar diseases in commercial corn hybrids and the relationship between damaged grains and expressão de enzymes in the grain in normal and reduced spacing, in Guarapuava - PR. The experimental design was a randomized complete block design with three replications in a factorial 3 x 8, totaling 24 treatments. The first factor is constituted by three levels, with the first foliar application of fungicides (Trifloxystrobin 150.0 g / l (15.0% w / v) + (Prothioconazole) 175.0 g / l (17.5% w / v) at a dose of 0.4 L ha-1in V8-eight stage expanded leaves, the second used if applied at a dose of 0.5 L ha-1 in phase VT - bolting, phenological scale of Ritchie and Hanway Benson ( 1993), and another control (without fungicide). The second factor consists of eight corn hybrids were divided into two groups according to their reaction to causative fungi of burned grain complex tolerant (AG 9045PRO AG 8041PRO, DKB 245PRO2 and 2B707PW) and susceptible (P 32R48H, DKB 390PRO, P 30F53H and P 30R50H), totaling 72 plots in each environment, in the 2013/2014 harvest. The first experiment was installed in the experimental area of the Universidade Estadual do Centro Oeste (UNICENTRO), Campus CEDETEG (conventional spacing of 0.70 m between rows), the second experiment was conducted on the Três Capões Farm, owned by the Company MLCV (Santa Maria Group) (reduced spacing 0.45 m), both in Guarapuava, PR. The experimental plot consisted of 4 rows of 5 m in length, with the floor area of the two central lines. The following characteristics were assessed: total chlorophyll content; area under the leaf disease progress curve (common rust and leaf spot Diplodia); percentage of damaged kernels; thousand kernel weight; grain yield and the expression of the enzymes catalase (CAT); alcohol dehydrogenase (ADH); malate dehydrogenase (MDH) and lipoxigenase (LOX) in the grain. There was a reduction in the area under disease progress curve (AUDPC) of common rust and leaf spot of Diplodia, with the use of fungicide (Trifloxystrobin Prothioconazole +), which is dependent on the hybrid and spacing used. Grain yield, percentage of damaged kernels, chlorophyll content and thousand kernel weight were influenced by the hybrid and the used fungicide. The fungicide (Trifloxystrobin + Prothioconazole) reduced the incidence of damaged kernels, with the largest reduction in hybrids considered susceptible. There is a relationship between increased expression of CAT enzyme and increased incidence of damaged kernels, because of the deterioration of grain, this being dependent on the hybrids tested. There is increased expression of enzymes (ADH) (MDH) and (LOX) for corn hybrids belonging to the group considered tolerant to fungi that cause rot grains. The application of fungicide (Trifloxystrobin + Prothioconazole) in two applications, V8 (eight sheets) and VT (bolting), increased the intensity of the LOX enzyme, being more evident in the reduced spacing.