|Bowden, Robert - Bob|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2002
Publication Date: 2/15/2003
Citation: ZELLER, K.A., BOWDEN, R.L., LESLIE, J.F. DIVERSITY OF EPIDEMIC POPULATIONS OF GIBBERELLA ZEAE FROM SMALL QUADRATS IN KANSAS AND NORTH DAKOTA. PHYTOPATHOLOGY. 2003. 93:874-880. Interpretive Summary: The fungus Gibberella zeae (also known as Fusarium graminearum) causes Fusarium head blight (FHB) of wheat and barley. This disease has caused billions of dollars in losses in the USA in the last decade. We isolated G. zeae from the top, middle, and bottom positions of infected wheat heads from small quadrats during severe FHB epidemics in Kansas in 1993 (KS) and North Dakota in 1994 (ND). We used a fingerprinting technique called AFLP to characterize the fungal strains. We found an average of about two strains of the fungus in each infected head, indicating that heads had multiple infections. Although genetic diversity of the fungus was high, there were no significant differences between the populations from North Dakota and Kansas. Our results suggest that these populations are parts of a single, well-mixed population that experiences frequent sexual recombination.
Technical Abstract: Gibberella zeae (anamorph Fusarium graminearum) causes Fusarium head blight (FHB) of wheat and barley. We isolated G. zeae from the top, middle, and bottom positions of wheat heads from 0.25 m² quadrats during severe FHB epidemics in Kansas in 1993 (KS) and North Dakota in 1994 (ND). We used three selective AFLP primer pairs to resolve 94 polymorphic loci among a total of 253 isolates. A subset of 26 isolates was also tested for vegetative compatibility groupings. Both methods indicated high genotypic variability and identified the same sets of isolates as probable clones. The mean numbers of AFLP multilocus genotypes per head were approximately 1.8 in each population, but were probably underestimates of the true means due to small sample size. We often recovered the same AFLP genotype from different positions in a single head, but only rarely from more than one head in the quadrat, suggesting a genetically diverse initial inoculum and limited secondary spread. The KS and ND samples shared no AFLP genotypes. All G. zeae isolates had high AFLP fingerprint similarity to reference isolates of G. zeae lineage VII. The genetic identity between the KS and ND populations was > 99% and the estimated effective migration rate was high (Nm ~70). Tests for linkage disequilibrium provide little evidence for nonrandom associations between loci. Our results suggest that these populations are parts of a single, panmictic population that experiences frequent recombination. Our results also suggest that a variety of population sampling designs may be satisfactory for this fungus.