Progress of bacterial blight on rice cultivars carrying different Xa genes for resistance in the field

Progress of bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae, was studied in the Philippines by planting six rice cultivars (IR24, IR36, IR54, IR60, IR64, and IR1695) carrying different Xa genes for resistance during the 1988 and 1990 seasons. Four epidemiological parameters, 1) disease incidence, 2) disease severity, J) area under the disease progress curve (AUDPC), and 4) apparent infection rate (r), were used to rank rice cultivars'resistance to X. o. oryzae. The susceptible check IR24 and resistant check IR1695 differed greatly in reaction to X. o. oryzae in the field during the 2-yr study. In the field, IR36, IR54, IR60, and IR64 showed high levels of resistance to X. o. oryzae compared with IR24