RAPD analysis was used to characterize the blast fungus populations attacking rice and its associated
weeds. Twenty eight M grisea isolates infecting four different hosts viz Oryza sativa, Eleusine coracana,
Echinocloa colonum and Digitaria sanguinalis were collected from contiguous rice fields. DNA of each
isolate was amplified using seven random primers. The DNA fingerprints generated using 7 primers
suggested that all the isolates were genetically distinct. Cluster analysis delineated the isolates into four
distinct groups each corresponding to the host specificity of the isolates. Several host specific bands
were also observed. These results indicate that isolates were strictly delimited by their host specificity
and gene flow among them was restricted.