Vegetative compatibility among Fusarium graminearum (Gibberella zeae) isolates from barley spikes in southern Manitoba

Vegetative compatibility groups (VCGs) were determined for 43 Fusarium graminearum Schwabe (Gibberella zeae (Schwein.) Fetch) isolates from barley using nitrate-nonutilizing mutants. Single isolates from 22 fields throughout southern Manitoba were used to evaluate regional diversity, and an additional 21 isolates from 10 spikes in 4 fields were used to estimate local diversity. Of 183 mutants generated, 67 utilized both nitrite and hypoxanthine (nit1), 89 utilized hypoxanthine but not nitrite (nit3), and 27 utilized nitrite but not hypoxanthine (NitM). A nit1 mutant from each isolate was paired on nitrate medium to either a nit3 or NitM mutant from all isolates. There were 21 VCGs among 22 isolates collected throughout Manitoba and 16 VCGs among 21 isolates used to estimate local diversity. When the 43 isolates were combined, 34 VCGs were identified. The average ratio of VCGs to isolates was 0.95 for isolates from different fields, 0.94 for isolates from different spikes within a field, and 0.90 for isolates within the same spike. The results indicate a high degree of VCG diversity in the F. graminearum population from barley spikes at the regional, local, and within-spike levels. This diversity should be considered when screening barley germplasm for fusarium head blight resistance.