Identification of a gene ovicidal to whitebacked planthopper, Sogatella furcifera Horvath in rice, Oryza sativa L.

39. Identification of a gene ovicidal to whitebacked planthopper, Sogatella furcifera Horváth in rice, Oryza sativa L. M. Yamasaki, A. Yoshimura and H. YASUI Plant Breeding Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan The whitebacked planthopper (WBPH), Sogatella furcifera Horváth is a serious insect pest of rice, Oryza sativa L. The rice ovicidal effect to WBPH is associated with the formation of watery lesions at the oviposition site (Suzuki et a!. 1996). The ovicidal effect is especially prevalent in Japonica varieties of Japan and most prominent at the maximum tillering stage. In the present study, a gene for ovicidal effect was identified and designated as Ovc. It was located on chromosome 6 through RFLP linkage analysis. We previously identified a major QTL for ovicidal effect on chromosome 6 (Yamasaki er a!. 1999) using recombinant inbred lines (RILs) derived from a cross between ovicidal Japonica variety Asominori and non-ovicidal Indica variety IR24 (Tsunematsu er a!. 1996). To identify the gene for ovicidal effect, the near-isogenic line which was heterozygous only for the QTL region on chromosome 6 was developed. For this purpose, one of the RILs was used for the original cross and the backcrosses with IR24 as a male parent were made to obtain BC2F1 plants. The BC2F1 plants which showed watery lesions were selected and backcrossed with IR24 as a female parent to generate BC3F1 plants. Finally, an isogenic plant which was heterozygous only for the chromosome 6 QTL was selected using 138 RFLP markers scattered on different rice chromosomes. The self-pollinated BC3F2 population(n = 99) was phenotyped for ovicidal effect. The WBPH population originated from adults collected from the paddy fields of Kyushu National Experiment Station in Chikugo, Fukuoka, in 1989. This population was maintained and used for infestation. Plants were infested at 11 weeks after seeding with 10 to 12 cultured WBPH females for two days in the room at 30°C and a 16h light:8h dark photoregime. After removing the insects, the plants were kept in the same room for three days. WBPH egg mortality was calculated for each individual of the mapping population. Both parents, Asominori and IR24 showed high and low egg mortality, respectively. The F1 plants showed high egg mortality. The BC3F2 plants showed a clear bimodal distribution for egg mortality and were classified into two groups; high and low egg mortality types (Fig. 1). The numbers of individuals showing high egg mortality (40-80%) and low egg mortality (0-20%) were 72 and 27, respectively. This ratio fitted the expected 3:1 ratio for single dominant gene segregation (f= 0.27, P 0.60), suggesting that the ovicidal effect was controlled by a single dominant gene. The dominant allele from Asominori caused the ovicidal effect. There is no previous report of a gene for resistance to insect oviposition in rice. Therefore, this gene is new and we designated it as Ovc (Ovicidal gene). RFLP linkage analysis revealed that the Ovc is tightly linked to RFLP marker R1954 on chromosome 6 (Fig. 2). The Ovc was located at the same position as the major QTL detected by QTL analysis. The marker R1954 can be useful for screening plants with Ovc. We are grateful to Drs. K. Sogawa and Y. Suzuki for providing insects and helpful comments. References Harushima, Y., M. Yano,A. Shomura, M. Sato, T. Shimano,Y. Kuboki, T. Yamamoto, S. Y. Lin, B. A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamanioto, Y. Nagamura, N. Kurata, 0. S. Khush and T. Sasaki, 1998. A high-density rice genetic linkage map with 2275 markers using a single F2 population. Genetics 148: 479-494. Suzuki, Y., K. Sogawa andY. Seino, 1996. Ovicidal reaction of rice plants against the whitebacked planthopper, Sogoieila furcifera HORVATH (Homoptera: Delphacidae). Appl. Entomol. Zool. 31: 111-118. Tsunematsu, H., A. Yoshimura, Y. Harushima, Y. Nagamura, N. Kurata, M, Yano, T. Sasaki and N. Iwata, 1996. RFLP framework map using recombinant inbred lines in rice. Breed. Sci. 46: 279-284. Yamasaki, M., H. Tsunematsu, A. Yoshimura, N. Iwata and H. Yasui, 1999. Quantitative trait locus mapping of ovicidal response in rice (Oryza sativa L.) against whitebacked planthopper (Sogatella furcifera Horváth). Crop Sci. 39: 1178-1183.

39. Identification of a gene ovicidal to whitebacked planthopper, Sogatella furcifera

Horváth in rice, Oryza sativa L.

M. Yamasaki, A. Yoshimura and H. YASUI

Plant Breeding Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan

The whitebacked planthopper (WBPH), Sogatella furcifera Horváth is a serious insect pest of rice, Oryza sativa L. The rice ovicidal effect to WBPH is associated with the formation of watery lesions at the oviposition site (Suzuki et a!. 1996). The ovicidal effect is especially prevalent in Japonica varieties of Japan and most prominent at the maximum tillering stage. In the present study, a gene for ovicidal effect was identified and designated as Ovc. It was located on chromosome 6 through RFLP linkage analysis.

We previously identified a major QTL for ovicidal effect on chromosome 6 (Yamasaki er a!. 1999) using recombinant inbred lines (RILs) derived from a cross between ovicidal Japonica variety Asominori and non-ovicidal Indica variety IR24 (Tsunematsu er a!. 1996). To identify the gene for ovicidal effect, the near-isogenic line which was heterozygous only for the QTL region on chromosome 6 was developed. For this purpose,

one of the RILs was used for the original cross and the backcrosses with IR24 as a male parent were made to obtain BC2F1 plants. The BC2F1 plants which showed watery lesions were selected and backcrossed with IR24 as a female parent to generate BC3F1 plants. Finally, an isogenic plant which was heterozygous only for the chromosome 6 QTL was selected using 138 RFLP markers scattered on different rice chromosomes. The self-pollinated BC3F2 population(n = 99) was phenotyped for ovicidal effect. The WBPH population originated from adults collected from the paddy fields of Kyushu National Experiment Station in Chikugo, Fukuoka, in 1989. This population was maintained and used for infestation. Plants were infested at 11 weeks after seeding with 10 to 12 cultured WBPH females for two days in the room at 30°C and a 16h light:8h dark photoregime. After removing the insects, the plants were kept in the same room for three days. WBPH egg mortality was calculated for each individual of the mapping population.

Both parents, Asominori and IR24 showed high and low egg mortality, respectively. The F1 plants showed high egg mortality. The BC3F2 plants showed a clear bimodal distribution for egg mortality and were classified into two groups; high and low egg mortality types (Fig. 1). The numbers of individuals showing high egg mortality (40-80%) and low egg mortality (0-20%) were 72 and 27, respectively. This ratio fitted the expected 3:1 ratio for single dominant gene segregation (f= 0.27, P 0.60), suggesting that the ovicidal effect was controlled by a single dominant gene. The dominant allele from Asominori caused the ovicidal effect. There is no previous report of a gene for resistance to insect oviposition in rice. Therefore, this gene is new and we designated it as Ovc (Ovicidal gene). RFLP linkage analysis revealed that the Ovc is tightly linked to RFLP marker R1954 on chromosome 6 (Fig. 2). The Ovc was located at the same position as the major QTL detected by QTL analysis. The marker R1954 can be useful for screening plants with Ovc.

We are grateful to Drs. K. Sogawa and Y. Suzuki for providing insects and helpful comments.

References

Harushima, Y., M. Yano,A. Shomura, M. Sato, T. Shimano,Y. Kuboki, T. Yamamoto, S. Y. Lin, B. A. Antonio, A.

Parco, H. Kajiya, N. Huang, K. Yamanioto, Y. Nagamura, N. Kurata, 0. S. Khush and T. Sasaki, 1998. A

high-density rice genetic linkage map with 2275 markers using a single F2 population. Genetics 148:

479-494.

Suzuki, Y., K. Sogawa andY. Seino, 1996. Ovicidal reaction of rice plants against the whitebacked planthopper, Sogoieila furcifera HORVATH (Homoptera: Delphacidae). Appl. Entomol. Zool. 31: 111-118.

Tsunematsu, H., A. Yoshimura, Y. Harushima, Y. Nagamura, N. Kurata, M, Yano, T. Sasaki and N. Iwata, 1996. RFLP framework map using recombinant inbred lines in rice. Breed. Sci. 46: 279-284.

Yamasaki, M., H. Tsunematsu, A. Yoshimura, N. Iwata and H. Yasui, 1999. Quantitative trait locus mapping of ovicidal response in rice (Oryza sativa L.) against whitebacked planthopper (Sogatella furcifera Horváth). Crop Sci. 39: 1178-1183.