ABSTRACT
Helminthosporiosis is among the major corn diseases. Two experiments were carried out with the aim of evaluating fungal sporulation in different culture media, inoculation methods and inoculum concentrations for Exserohilum turcicum. For sporulation in different culture media, six different substrata were tested: potato sucrose agar (BSA), maize leaf extract (FM), potato dextrose agar (PDA), V8 juice agar (V8), lactose casein hydrolysate agar (LCHA) and semi-selective medium De Rossi and Reis (DRR) subjected to two light regimes, 12 hours photoperiod and continuous dark. In the second assay, two inoculation methods were evaluated: spray and deposition of the inoculum in the seedling cartridge, testing the concentrations of 5x103, 10x103, 15x103 20x103, 25x103 conidia / mL, and in the second one, 0.5 mL at the concentration of 20x103 conidia/mL were deposited in the cartridges. For both methods, inoculation was done in stage V4 (fourth expanded leaf, showing collar, ligule and visible auricles) and kept in a humid chamber for 24 hours at the temperature of 25 0C. Fifteen days after inoculation, the estimated severity and the lesion area were evaluated. The experimental design was completely randomized with four replicates, and data were subjected to analysis of variance and regression. The highest number of conidia.cm-2 was obtained in the DRR medium, independent of the light regime. The spray method was effective at the concentrations of 15x103, 20x103 and 25x103 conidia/mL.
Keywords
inoculum concentration; helminthosporiosis; Helminthospooium turcicum; culture medium; Zea mays
