ABSTRACT
The performance of seed treatment products for maize usually is evaluated in field experiments, where it is difficult to assess their effects on specific important pathogens such as fungi in the genus Fusarium. To evaluate three fungicidal seed treatments (captan, difenoconazole, and fludioxonil) against six Fusarium species that infect maize seed or seedlings, we conducted experiments in the laboratory and in growth chambers. In the laboratory experiments, treated and nontreated seeds of two maize hybrids were incubated on the surface of an agar medium colonized by each of 12 Fusarium isolates. The fungi did not reduce seed germination, but most Fusarium isolates caused decay of the seed and radicle, and arrested the development of the radicle. All three fungicides significantly reduced the colonization and decay of the seeds and radicles by Fusarium isolates and resulted in greater radicle lengths, but there were significant interactions between the effects of fungicide treatments and Fusarium isolates. Overall, difenoconazole was the most effective fungicide for the prevention of seed colonization and decay. Fludioxonil was overall the most effective fungicide in terms of increased radicle length, particularly when seed was exposed to isolates of F. graminearum, which were among the most aggressive isolates in the experiments. In the growth chamber experiments, seeds were planted in a Fusarium-infested potting medium, which resulted in lower emergence, shoot length, root length, and dry weight of seedlings compared to the noninfested control. Some isolates also caused root rot symptoms. All three fungicides significantly improved shoot and root length and root health, difenoconazole and fludioxonil significantly improved emergence, and only difeno-conazole significantly improved dry weight compared to the nontreated control. There were significant rank correlations between the results of the laboratory and growth chamber experiments in terms of relative aggressiveness of the isolates and relative efficacy of the fungicides. The laboratory experiments were more sensitive in terms of detecting differences in fungicide performance. These results indicate that all three fungicides were effective against Fusarium, but difenoconazole and fludioxonil generally were more effective than captan; the fungicides also differed in efficacy against different Fusarium species.
