Fusarium species infecting soybean roots: Frequency, aggressiveness, yield impact and interaction with the soybean cyst nematode

Abstract

Fusarium root rot is a widespread and common disease in soybean. Several Fusarium species have been reported to infect soybean roots but their occurrence, aggressiveness and impact on yield have not been quantified. To gain a better understanding of the importance of root-infecting Fusarium species in soybean productivity in Iowa, a three year root survey, and greenhouse and field experiments were conducted in order to accomplish the following objectives, 1) characterize the frequency of Fusarium species associated with soybean roots from Iowa soybean fields, 2) determine aggressiveness of predominant Fusarium species towards soybean, 3) estimate the impact of Fusarium species on growth and yield of soybean plants and 4) determine whether there is an interaction between SCN infestation and Fusarium root rot species in soybean roots. Using morphological and molecular techniques, 15 Fusarium species were identified in association with soybean root. Fusarium oxysporum, F. solani, F. acuminatum, and F. graminearum were most frequently isolated and most prevalent at the county and field level. Aggressiveness of isolates representing the most frequent species was tested under greenhouse and field conditions. In the greenhouse, aggressiveness differed between species and among isolates at V3 soybean growth stage; F. graminearum caused the most severe root rot and detrimental effects on root system morphology, followed by F. virguliforme and F. proliferatum. Significant variation in aggressiveness was observed among F. oxysporum isolates, some of which caused severe damping off. In the field, low root rot severity was observed. Mean yield was not significantly reduced but significant linear relationships were found for some isolates between yield and root health measures. To determine whether SCN infestation enhances root rot disease in soybean, greenhouse