ABSTRACT
The variation in the reaction of a bacterial isolate depends on the cultivar of the host plant. The host crop plant with different genetical makeup reacts differently to the same bacterial isolate to produce susceptible or resistant reaction, and this forms the basis for variation in the given bacterial species or pathovars. The isolates of the pathovars, on the basis of their reaction to different genotypes/cultivars/varieties of the host crop, are further subdivided into races. These races are specific in attacking the particular genotype of the crop while not to the other genotype. On the basis of differential reaction of the host cultivars the races of the given pathogen is determined.
