RELATIONSHIP BETWEEN PHYLOGENY AND PATHOTYPE FOR THE BACTERIAL-BLIGHTPATHOGEN OF RICE

Several transposable elements were isolated from the genome of Xanthom onas oryzae pv. oryzae. These elements and an avirulence gene isolated from X. oryzae pv. oryzae were used as hybridization probes for a col lection of X. oryzae pv. oryzae strains from the Philippines. Each of the sequences was present in multiple copies in all strains examined a nd showed distinct patterns of hybridizing bands. Phenograms were deri ved from the restriction fragment length polymorphism data obtained fo r each of the individual probes and for pooled data from multiple prob es. The phenograms derived from the different probes differed in topol ogy and, on the basis of bootstrap analysis, were not equally robust. For all of the probes, including the avirulence gene, some groups (eve n some haplotypes) consisted of multiple races. The strains were group ed into four major clusters on the basis of the two probes giving the highest bootstrap values. These groups were inferred to represent phyl ogenetic lineages. Three of the six races of X. oryzae pv. oryzae appe ared in more than one of the lineages, and another was present in two sublineages. For three of the races, strains representing different ph enetic groups were inoculated on rice cultivars carrying 10 resistance genes. Two new races were differentiated, corresponding to pathogen l ineages identified by DNA typing. On the basis of DNA and pathotypic a nalyses, together with information on the spatial and temporal distrib ution of the pathogen types from this and other studies, a general pic ture of X. oryzae pv. oryzae evolution in the Philippines is presented .