All-India Coordinated Rice Improvement Project, Hyderabad-30, Andhra Pradesh
*AICRIP Publication No. 45.
Genetics of resistance to bacterial leaf blight was studied in two crosses involving two resistant donor parents, BJ 1 and Sigadis, each crossed with IR 8. Due to the existence of pathogenic specialization of the causal organism, X. oryzae, the studies were carried out through artificial inoculation with specific isolates. Isolates H 14, H 89 and H 146 were employed in the cross IR 8 × BJ 1, and isolates H 66 and H 125 in the cross IR 8 × Sigadis, IR 8 being susceptible to all the five isolates.
In the cross IR 8 × BJ 1 digenic (3 resistant: 13 susceptible), trigenic (9 resistant: 55 susceptible) and tetragenic (27 resistant: 229 susceptible) inhibitory ratios with complementary action involved in the latter two were obtained for resistance to H 14, H 89 and H 146 respectively. Resistance in all cases was dominant but the expression was controlled by an inhibitory gene. The dominant inhibitory gene and the hypostatic gene involved in all three cases were proved to be the same, and in addition, one of the two non-hypostatic genes involved in resistance to H 146 was revealed to be the same as the non-hypostatic gene involved in resistance to H 89. This system renders a plant resistant to H 146 to be necessarily resistant to H 14 and H 89 and plants resistant to H 89 necessarily resistant to H 14. The importance of genetic studies in plant breeding, which in the present case, identified the key isolate H 146, has been pointed out.
Resistance to two isolates studied in the cross IR 8 × Sigadis was found to be recessive unlike in BJ 1 cross, where resistance to all three isolates involved was dominant. Trigenic inhibitory gene ratio of 55 resistant: 9 susceptible was obtained for resistance to H 66, and trigenic ratio of 45 susceptible: 19 resistant was obtained in the segregation for resistance to H 125.
No restriction was evident, in both the crosses studied on the transfer of resistance to bacterial leaf blight to good genetic background of dwarf plant types.
