THE RELATIONSHIP BETWEEN LINEAGE AND VIRULENCE IN PYRICULARIA-GRISEA IN THE PHILIPPINES

The relationship between phylogeny and pathotype was examined for a se lected group of isolates of the blast fungus Pyricularia grisea from t wo sites in the Philippines. Based on DNA fingerprinting and cluster a nalysis with the repetitive DNA probe MGR586, isolates fell into sever al distinct groups. Probing blots of the MGR-defined haplotypes with a virulence genes A VR2- YAMO and PWL2 produced single or multiple copy profiles that grouped identically to those from the MGR analyses. A se t of 234 isolates, representing six of these groups or putative lineag es, was selected for analysis of virulence spectrum. These isolates we re tested on 15 rice cultivars and six near-isogenic lines. A total of 71 distinct pathotypes (virulence patterns) was detected on the 21 ho sts tested. Multiple pathotypes were seen for each of the six lineages analyzed. Although there was no obvious relationship between lineage and pathotype, the distribution of virulence was nonrandom with respec t to lineage for a given cultivar. Although reactions were variable fo r some host-lineage combinations (both compatible and incompatible iso lates were found for 43 of the 123 host-lineage combinations analyzed) , consistent incompatibility was observed for the majority of host-lin eage interactions. In 80 of the 123 host-lineage combinations tested ( 65%), no compatible reaction was found, although an average of 39 isol ates was tested per lineage per host. For each lineage, between nine a nd 16 cultivars were resistant to all isolates. Individual cultivars s howed different spectra of resistance with respect to the pathogen lin eages tested. The indica and japonica cultivars tested appeared to hav e complementary spectra of resistance. The implications of these obser vations for resistance breeding are discussed.