Submitted to: National Fusarium Head Blight Forum Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/10/2001
Publication Date: N/A
Technical Abstract: Routine surveys of seed quality of soybean (Glycine max) grown in South Brazil revealed unexpected infection with Fusarium graminearum. Seemingly symptomless seeds were surface disinfested with 1.0% sodium hypochlorite for 2 minutes and plated on water agar or 1/4 PDA. After 8 days, spores were examined from fungal colonies growing from the seeds and determined to be members of the F. graminearum species complex. Seed lots varied in the percentage of infected seed, ranging from 0 - ca. 20%. To determine if the fungus was pathogenic to soybean, 8 strains of the fungus derived from soybean were added to soil at a rate of 103 macroconidia/ ml or pods were inoculated each with 104 macroconidia. Seedlings grown in infested soil developed small necrotic lesions in the crown and upper tap root. Pods inoculated with the fungus developed large (greater than 1 cm), dark brown, necrotic lesions. Younger pods inoculated with the fungus blighted and dropped from the plant. Cultures of F. graminearum were recovered fro lesions on the crown, roots and pods of inoculated plants. The lineage of the F. graminearum fungus infecting soybean was determined by obtaining the DNA sequence from the EF1-alpha gene from five strains and comparing it to strains of known lineage. Strains of the fungus from soybean grown in Brazil were from lineage 2 or lineage 8. Two strains of F. graminearum lineage 7 from the U.S. caused similar symptoms on soybean. Mycotoxin tests on naturally and artificially infected seed are being conducted.