IMPORTANCE OF DIFFERENT PATHWAYS FOR MAIZE KERNEL INFECTION BY FUSARIUM-MONILIFORME

The relative importance of several infection pathways (silks, stalks, and seed) leading to kernel infection of maize hybrids by Fusarium mon iliforme was investigated in field experiments in 1993 and 1994. Syste mic movement of specific fungal strains within plants was detected by using vegetative compatibility as a marker. Transmission of F. monilif orme from inoculated seed to stalks and developing kernels was detecte d in two of three field experiments; the seed-inoculated strain was de tected in kernels on approximately 10% of ears. The percentage of kern els infected with the seed-inoculated strain ranged from 0 to 70%, wit h a mean of 0 to 2.5% (0 to 8.3% of F. moniliforme-infected kernels). Other pathways to kernel infection were more effective than seed trans mission and systemic infection. F. moniliforme strains inoculated into the crowns and stalks of plants were found throughout the stalks and in up to 95% of the kernels in individual plants. Infection through th e silks was clearly the most effective pathway to kernel infection. Th is was the only inoculation method that significantly increased overal l incidence of F. moniliforme infection in kernels; the silk-inoculate d strain infected up to 100% of the kernels in individual ears, with a treatment mean as high as 83.7% of kernels. When plants were silk-ino culated the percentage of kernels infected by other F. moniliforme str ains from the seed or stalk was reduced, apparently due to competition among strains. This study provides evidence that systemic development of F. moniliforme from maize seed and stalk infections can contribute to kernel infection, but silk infection is a more important pathway f or this fungus to reach the kernels.