34. Identification of a new resistance gene to brown planthoppers in Japan

2) Tohoku National Agricultural Experiment Station, Yotsuya, Ohmagari, 014-01 Japan

The brown planthopper (BPH, Nilaparvata lugens Stal.) is a great threat to rice culture in southern Japan. Breeders are engaged in developing resistant varieties. Four resistance genes (Bph-1, bph-2, Bph-3, and bph-4) are being used in breeding programs, but more resistance genes would be needed in the future. Ikeda (1985) and Kaneda (1984) screened rice germplasm for BPH resistance by testing the reactions of varieties to BPH biotype I (wild type), biotype II (infesting rice with Bph-1), and biotype III (infesting rice with bph-2). They then crossed the varieties with certain test-strains having known genotypes to identify the resistance genes involved. Three varieites, Thai Collection 5, Thai Collection 11 and Chin saba, showed resistance to all three biotypes, indicating that their resistance genes were different from either Bph-1 of bph-2. Their test-cross with Milyang 23 having no resistance gene showed that their resistance genes were recessive. They were then testcrossed with Babawee having bph-4. The F\2\ populations showed a 7 resistant: 9 susceptible ratio, indicating that their resistance genes were different from bph-4. Since they were neither bph-2 nor bph-4, they must be new genes.

To determine whether one or more gene(s) exist in the three varieties, they were intercrossed in reciprocal directions. In the bulk seedling test for resistance, materials were seeded in 20 rows including two rows of check varieties on a plastic tray (15.5x26cm) with 13 seeds per row. Nipponbare was used as the susceptible check and BP 4 with Bph-1 as the resistant check. The seedings at the first-leaf stage were inoculated with second to third instar nymphs of BPH of biotype I. The reaction of seedlings was recorded seven days after inoculation when the susceptible check was killed while the resistant seedlings had little visible injury. The test showed that almost all the F\1\ and F\2\ plants of crosses between the three varieties mentioned above (6 crosses in total, including reciprocals) were resistant. Although a few F\3\ seedlings died or wilted after unfolding the second leaf, such death was also seen in the resistant check possible as the result of deterioration under low light intensity.

If the parental varieties of a cross had different recessive genes for resistance, the F\1\ would be susceptible and the F\2\ would segregate into 7 resistant: 9 susceptible types. The observed reactions of the crosses demonstrate that the three varieties have an identical recessive gene for BPH resistance. Khush et al. (1985) reported a new recessive gene bph-5, which was found in ARC 10550. It is effective to a Bangladesh biotype, but not effective to other biotypes of East and Southeast Asia. Therefore, the new gene we have found differs from bph-5. It will be named after some more tests.

Ikeda, R., 1985. Studies on the inheritance of resistance to the rice brown planthopper (Nilaparvata lugens Stal) and the breeding of resistant rice cultivars. Bull. Nat. Agric. Res. Cent. 3: 1-54.

Ikeda, R. and C. Kaneda, 1985. New genes for resistance to the brown planthopper in rice. Jpn. J. Breed. 32, Supple. 2: 130-131 (in Japanese).

Kaneda, C., 1984. Studies on breeding japonica rice resistant to the brown planthopper. Bull. Nat. Agric. Res. Cent. 2: 1-74.

Khush, G.S., A.N.M., Reqaul Karim and E.R. Angeles, 1985. Genetics of resistance of rice cultivar ARC10550 to Bangladesh brown planthopper biotype. J. Genet. 64(2&3):121-125.