Effects of inoculation position, timing, macroconidial concentration, and irrigation on resistance of maize to Fusarium graminearum infection through kernels

To standardize a kernel wound inoculation technique for evaluation of maize genotypes for resistance to gibberella ear rot, four parameters associated with its application were investigated: inoculation position, time of inoculation after silk emergence, macroconidial concentration, and irrigation. Two moderately resistant (Pride K127 and Funk G4106) and two susceptible (Pioneer 3953 and Dekalb DK-415) hybrids were inoculated through the husk by wounding 3-4 kernels in the centre of the ear with four stainless steel pins that had previously been dipped in a macroconidial suspension of Fusarium graminearum. Disease severity was determined at harvest. In four experiments conducted in 1993 and 1994, ears were inoculated using three inoculation positions (tip, centre, and butt of the ear); seven conidial suspension concentrations ranging from 0 to 2 X 10(6) conidia/mL; 12 (1993) and 9 (1994) different times of inoculation, ranging from 0 to 44 days post-silk emergence; and wounding and a silk channel injection techniques under irrigated and nonirrigated conditions. Disease severity was highest with inoculations made in the centre of the ear. Disease severity increased with increasing conidial concentrations but decreased with increasing kernel/silk age. Irrigation tended to lower disease severity and did not significantly enhance differentiation between genotypes. Best differentiation between genotypes was obtained when inoculations were made in the centre of the ear at approximately 15 days post-silk emergence and with a suspension of at least 10(5) conidia/mL suspension.