Abstract
The effect of host age on the expression of resistance to seven isolates (races) of Xanthomonas campestris pv. oryzae, causing bacterial blight, in nine rice cultivars/lines was studied. Seedling and aduJt plant resistance was distinct and distinguishable. Stability of seedling resistance varied in different cultivar isolate combinations. The growth stage of the plant when adult plant resistance became operative ranged from maximum tillering (50 days after sowing, DAS) to the booting stage (70 DAS) in different cultivar/isolate combinations. The disease severity in some cultivar/isolate combinations gradually decreased from seedling to boot stage, whereas in others an abrupt decline in disease severity was noticed at/or after maximum tillering. The expression of adult plant resistance was differential.
