R. I. Hamilton

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 × 10 6 spores per milliliter in 1990, 1991, and 1992; and 3) three spore concentrations (2 × 10 5 , 5 × 10 5 , and 2 × 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 ml of a 5 × 10 5 spores per milliliter suspension injected into the silk channel at approximately 6 days after silk emergence should give adequate differentiation of genotypes

Comparison of techniques for inoculating maize silk, kernel, and cob tissues with Fusarium graminearum

Six inoculation techniques differing in the method of application of a conidial suspension and in the part of the ear inoculated were evaluated for their effectiveness in assessing maize (Zea mays) resistance to ear rot caused by Fusarium graminearum. Silk channel injection and ear-tip flooding inoculation techniques were carried out 7 days after silk emergence. The other four techniques (wound-spray, kernel-stab, pipe cleaner, and cob-tip) were carried out 15 days after silk emergence. A 7-class rating scale was used to assess disease severity at harvest. Significant differences (P < 0.05) in incidence and severity of ear rot symptoms were detected among the inbred lines and inoculation techniques. There were significant inbred x inoculation technique interactions, but inoculation techniques intended to measure the same resistance mechanism ranked inbred lines similarly in three of the four environments. All inoculation techniques except the ear-tip flooding technique identified CO325 as the most resistant inbred. Among the techniques used, the silk channel and the kernel-stab techniques appeared to be the most effective in measuring silk and kernel resistance, respectively.

Resistance of maize hybrids and inbreds following silk inoculation with three isolates of Fusarium graminearum

Maize hybrids and inbred lines, including six quality protein maize (QPM) inbreds, were evaluated for resistance to ear rot after silk inoculation with three Fusarium graminearum isolates. Conidial suspensions were injected into the upper silk channel to approximate natural infection. Although significant isolate effects and genotype × isolate interactions were observed, the rankings of maize genotypes were similar across isolates. One of the isolates appeared to be less aggressive, and this may account for the observed isolate effects and interactions

CO388 and CO389 corn inbred lines

CO388 and CO389 are short-season corn inbred lines with improved resistance to silk infection by Fusarium graminearum. These inbreds are the first to be released from a public breeding program with improved resistance to ear rot; they can be used by maize breeders as a source of resistance. Both inbreds exhibit good combining ability and average to superior lodging resistance in hybrids. Key words: Corn, maize, Zea mays, cultivar description, ear rot, Fusarium

CO430, CO431 and CO432 corn inbred lines

CO430, CO431 and CO432 are short-season corn inbred lines with improved resistance to silk infection by Fusarium graminearum. These inbreds exhibit average combining ability, average to superior lodging resistance in hybrids and were rated as having excellent emergence and seedling vigour. Key words: Corn, maize, Zea mays, cultivar description, ear rot, Fusarium

CO429 corn inbred line

CO429 is a short-season corn inbred line with good combining ability, average to superior lodging resistance in hybrids, and excellent emergence and early season vigour. Key words: Corn, maize, Zea mays, cultivar description

CO427 and CO428 corn inbred lines

CO427 and CO428 are short-season corn inbred lines with excellent combining ability, average to superior lodging resistance in hybrids and excellent emergence and early season vigour. Key words: Corn, maize, Zea mays, cultivar description