Abstract
Infection from strains of Xanthomonas campestris pv. oryzae on IR8, IR20 and IR1545 by the leaf clipping, pin-pricking and spray methods of inoculation suggested that neither lesion length nor disease score were affected. The incubation period was varied by methods of inoculation, but not by varietal resistance. Breeding lines derived from TKM 6 for Xa4 and DZ192 for xa5 sources of resistance were consistent with respective bacterial strains of the same virulence group, at maximum tillering stage of plant growth. The resistance was not complete. Significant differences in virulence between group 1 strains to TKM 6 and its derivatives and group 2 strains to TKM 6, DZ192 and their derivatives were observed. The effect of leaf age, as well as plant age, to infection varied from young to old, but the significant lesion length was observed only in compatible rice cultivar and bacterial strain combinations. The lesion length of breeding lines having “adult plant” resistance, such as IR1695 and IR944, gradually decreased from vegetative stage to reproductive stage against strains of all virulence groups evaluated. Lesion length of cultivars of moderate susceptibility comparable to partial resistance, was decreased significantly when inoculum dosage was lower, while the lesions on lines with adult plant resistance were not different from IR 8, the check variety.
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