A New Gene for Resistance to Bacterial Blight in Rice1

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Abstract
The mode of inheritance and allelic relationships of the genes for resistance to bacterial blight caused by Xanthomonas campestris pv oryzae (Ishiyama 1922) Dye 1978 in 58 rice (Oryza saliva L.) cultivars were studied in the field. The analysis of F1 and F2 populations from the crosses of resistant cultivars and susceptible ‘TN1’ revealed that single dominant genes conditioned resistance in each of 48 cultivars whereas single recessive genes conveyed resistance in 10 remaining cultivars. The allele tests indicated that the 48 cultivars have the Xa 4 gene for resistance. The recessive genes for resistance in eight cultivars are allelic to xa 5. However, the recessive genes for resistance in ‘Khao Lay Nhay’ and ‘Sateng’ are allelic to each other but are nonallelic to and segregate independently of Xa 3, Xa 4, xa 5, Xa 7, and xa 8. This new recessive gene is linked with Xa 6 with a crossover value of 5.9%. Thus cultivars Khao Lay Nhay and Sateng have a new gene for resistance, which was designated xa 9.