EFFECT OF MACROCONIDIAL SUSPENSION VOLUME AND CONCENTRATION ON EXPRESSION OF RESISTANCE TO FUSARIUM-GRAMINEARUM IN MAIZE

The effects of volume and concentration of macroconidial suspensions applied to maize silks on resistance to Fusarium graminearum infection were investigated on three maize hybrids (Pride K127, Pioneer 3953, and Dekalb DK-415). Plants were inoculated in the field by injecting a spore suspension into the silk channel of individual ears. Disease severity and deoxynivalenol (DON) concentration in grain were determined at harvest. In three experiments, plants were inoculated with 1) six conidial suspension volumes ranging from 0.5 to 10 ml in 1991 and 1992; 2) seven spore concentrations ranging from 0 to 2 X 10(6) spores per milliliter in 1990, 1991, and 1992; and 3) three spore concentrations (2 X 10(5), 5 X 10(5), and 2 X 10(6) spores per milliliter) inoculated at six silk ages (1, 3, 5, 7, 12, and 18 days after silk emergence) in 1991 and 1992. On average, Pride K127 was most resistant, followed by Pioneer 3953 and Dekalb DK-415. Disease severity, and in most cases DON, increased with increased conidial suspension volume and concentration, with greater effects in susceptible hybrids. Disease severity decreased with silk age over all spore concentrations. When screening for resistance to infection via the silk, 2 mi of a 5 X 10(5) spores per milliliter suspension injected into the silk channel at approximately 6 days after silk emergence should give adequate differentiation of genotypes.