Factors underlying to increased prevalence of Pythium disease following
non-targeted fungicide application to corn seeds
Abstract
Microbial communities are essential for soil health, but fungicide
application can have major effects on their structure, and it is
difficult to predict whether non-target pathogens in the soil will cause
major crop damage. Using collected soil with a history of poor corn (Zea
mays) seedling emergence, we demonstrate that the poor emergence of corn
seedlings from seeds coated with the fungicide tebuconazole is primarily
due to infection of surviving soil pathogens, particularly Pythium
complexes that are not targeted by fungicide tebuconazole. We determined
that the bases for the increased infection by non-target species of
Pythium were: 1) the selective fungicidal activity of seed-applied
tebuconazole showed a low level of control against Pythium species but
had a significant effect on soil fungi, thereby releasing Pythium spp.
from competition with other soil microorganisms; 2) the growth of the
natural enemies in soil, Trichoderma spp., was strongly inhibited by
tebuconazole; and 3) low temperature was the key factor of triggering
fatal injury of Pythium pathogens to corn seeds. Taken together, the
non-target effects of tebuconazole are likely not significant under
favorable plant growing conditions, but are considerable as a result of
low temperature stress.