Kanto PL10, resistant line to green rice leafhopper (GRH), was bred from crosses between SML17 and Nipponbare. Its cross combination is represented as SML17/3*Nipponbare. In the present study, we determined the chromosomal location of a new GRH resistance gene in Kanto PL10.

For the linkage analysis of the GRH resistance gene with rice RFLP markers, we used 87 F₂ plants derived from the cross between Kanto PL10 and Nipponbare. To evaluate GRH resistance, we employed a newly developed technique, in which both nymph survival and growth rates were used as criteria (Hirae et al. 2002). 87 F₂ plants showed a discrete distribution, segregating into 69 resistant and 18 susceptible plants (Fig. 1). The segregation ratio fitted to a 3:1 ratio (chi²=0.97), indicating that the GRH resistance was controlled by a single dominant gene. From the result of progeny test using F₃ strains, 69 resistant plants were classified into 17 homozygote and 52 heterozygote.

To determine the chromosomal location of the resistance gene, we first analyzed the graphical genotype of Kanto PL10 using 144 markers. Several segments originated from SML17 were detected. Segregation of the markers located in these segments and the resistance gene was

analyzed with the software MAPMAKER/EXP ver.3.0. RFLP analysis using F₂ plants showed that the resistance gene was located between Y3635R and C708 on chromosome 4 (Fig. 2). So far, five genes for resistance to GRH have been mapped on rice chromosomes using RFLP or simple sequence repeats (SSR) markers, Grh1 on chromosome 5(Tamura et al. 1999), Grh2 and Grh4 on chromosome 11 and 3, respectively (Fukuta et al. 1998; Yazawa et al. 1998), Grh3 (t) on chromosome 6 (Saka et al. 1996), and Grh5 on chromosome 8 (Fujita et al. 2003). There have been no genes for resistance to GRH on chromosome 4. Therefore, we designated the new resistance gene as Grh6 (Green rice leafhopper resistance 6).

References

Fujita, D., K. Doi, A. Yoshimura and H. Yasui, 2003. Mapping of a new resistance gene for green rice leafhopper introgressed from Oryza rufipogon Griff. into cultivated rice, Oryza sativa L. RGN 20: 79-80.

Fukuta, Y., K. Tamura, M. Hirae and S. Oya, 1998. Genetic analysis of resistance to green rice leafhopper (Nephotettix cincticeps Uhler) in rice parental line, Norin-PL6, using RFLP markers. Breed. Sci. 48: 243-249.

Hirae, M., Y. Fukuta, K. Tamura and S. Oya, 2002. A method for evaluation of rice resistance to Green rice leafhopper Nephotettix cincticeps(Uhler), based on nymphal growth. Jpn. J. Appl. Entomol. Zool. 46: 178-181 (Japanese with English summary).

Saka, N., T. Toyama, T. Tuji, H. Nakamae and T. Izawa, 1997. Fine mapping of green ricehopper resistant gene Grh-3 (t) and screening of Grh-3 (t) among green ricehopper resistant and green leafhopper resistant cultivars in rice. Breed. Sci. 47 (suppl. 1): 55 (in Japanese).

Tamura, K., Y. Fukuta, M. Hirae, S. Oya, I. Ashikawa and T. Yagi, 1999. Mapping of Grh1 locus for green rice leafhopper resistance in rice using RFLP markers. Breed. Sci. 49: 11-14.

Yazawa, S., H. Yasui, A. Yoshimura and N. Iwata, 1998. RFLP mapping of genes for resistance to green rice leafhopper (Nephotrttix cincticeps Uhler) in rice cultivar DV85 using near isogenic lines. Sci. Bull. Fac. Agr. Kyushu Univ. 52:169-175 (Japanese with English summary).