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 th e 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 pr edominant pathotypes in Arkansas were examined. Total DNA of each isol ate was restricted with EcoR1 and probed with a dispersed repeated MGR 586 DNA probe. MGR586 DNA fingerprint groups were identified based on DNA restriction fragment length polymorphism similarities. Seven disti nct 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) previ ously reported for M. grisea. Four fingerprint groups (A, B, C, and D) were found in both fields. Group A was the predominant group represen ting 72% and 52% of the isolates collected from the two fields. Hierar chical diversity analysis demonstrated that the majority of genetic va riability 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 t he DNA fingerprint groups were examined for virulence on each of two s ets of differential rice cultivars. Although certain fingerprint group s were composed of a single pathotype, the data indicated that other g roups in the contemporary population were composed of isolates that ar e quite heterogeneous with respect to virulence. Furthermore, contempo rary isolates in one fingerprint group (group B) were a different path otype from an older reference isolate of the same fingerprint group. T hus, the relationship between pathotype and DNA fingerprint group in c ontemporary populations of M. grisea in the United States apparently i s quite complex.