DNA-FINGERPRINTING TO EXAMINE MICROGEOGRAPHIC VARIATION IN THE MAGNAPORTHE-GRISEA (PYRICULARIA-GRISEA) POPULATION IN 2 RICE FIELDS IN ARKANSAS

DNA fingerprinting was used to analyze microgeographic variation in the Magnaporthe grisea population in Arkansas. One hundred and thirteen isolates were collected from two commercial rice fields (cu. Newbonnet) in 1991. In addition, several reference isolates representing the predominant pathotypes in Arkansas were examined. Total DNA of each isolate was restricted with EcoR1 and probed with a dispersed repeated MGR586 DNA probe. MGR586 DNA fingerprint groups were identified based on DNA restriction fragment length polymorphism similarities. Seven distinct fingerprint groups (designated A through G) were identified among the field and reference isolates. These seven fingerprint groups were very similar to seven of the eight fingerprint groups (lineages) previously reported for M. grisea. Four fingerprint groups (A, B, C, and D) were found in both fields. Group A was the predominant group representing 72% and 52% of the isolates collected from the two fields. Hierarchical diversity analysis demonstrated that the majority of genetic variability was distributed within sample locations within a field. Thus, the initial source or sources of inoculum may have been a mixture of the four different fingerprint groups. Isolates representing all of the DNA fingerprint groups were examined for virulence on each of two sets of differential rice cultivars. Although certain fingerprint groups were composed of a single pathotype, the data indicated that other groups in the contemporary population were composed of isolates that are quite heterogeneous with respect to virulence. Furthermore, contemporary isolates in one fingerprint group (group B) were a different pathotype from an older reference isolate of the same fingerprint group. Thus, the relationship between pathotype and DNA fingerprint group in contemporary populations of M. grisea in the United States apparently is quite complex.