The green rice leafhopper (GRH), Nephotettix cincticeps Uhler
is a serious insect pest of rice in East Asia. The leafhopper causes either
direct damage to the rice plant by sucking the sap or by transmitting
several viral diseases. Germplasm resistant to GRH has been found in Indica
varieties such as IR24 and DV85. To date, four resistance genes, Grh1,
Grh2, Grh3 and Grh4, have been identified (Saka et
al. 1997; Fukuta et al. 1998; Yazawa et al. 1998; Tamura
et al. 1999).
To identify new resistance genes to GRH, four Indica varieties with GRH
resistance were screened by antibiosis test. IR20965-26-1-2, Gadur and
Garia were highly resistant and ASD7 was moderately resistant. The resistant
varieties were crossed with a susceptible Japonica variety Taichung65.
The F2 individuals derived from the respective crosses were
evaluated by antibiosis test at the seedling stage, to find QTLs responsible
for resistance to GRH. Seedlings were infested with 7-10 first- or second-instar
nymphs from an insect population collected in Fukuoka Prefecture in 1991.
Antibiosis was scored as nymph mortality four days after infestation.
After evaluation, the plants were transplanted in the field. Leaf samples
were collected and the genomic DNA was extracted for RFLP genotyping.
A total of 88 RFLP markers scattered in the rice genome were used for
constructing RFLP linkage map of respective crosses. QTL analyses for
resistance to GRH were conducted using MAPMAKER/QTL v1.1, with a threshold
The resistant varieties, IR20965-26-1-2 and Gadur showed high nymph mortality,
nearly 100%, whereas ASD7 showed unstable resistance, 50-100% nymph mortality.
Taichung65 was susceptible, without nymph mortality. Frequency distribution
of nymph mortality in each F2 population was continuous and
did not represent any kind of discrete segregation. A total of eight QTLs
for antibiosis were detected on six different loci in four cross combinations
(Table 1). Each QTL explained 25.2% to 70.0% of the phenotypic variance.
All Indica alleles on the QTLs contributed to the increase in nymph mortality.
Six of the eight QTLs corresponded with the genes resistant to GRH based
on chromosome location. Four QTLs,
qGRH-5, qGRH-6, qGRH-11 and qGRH-3, appeared
to coincide with Grh1, Grh3, Grh2 and Grh4,
respectively (Saka et al. 1997; Fukuta et al. 1998; Yazawa
et al. 1998; Tamura et al. 1999).
The four Indica varieties carried a few genes resistant to GRH. ASD7 had
both Grh1 and Grh3. Although the resistance of ASD7 was
moderate, the F2 segregants carrying both Grh1 and Grh3
were highly resistant. The highly resistant varieties, Gadur and Garia,
carried the same resistance genes, Grh2 and Grh4. The high
level of resistance of IR20965-26-1-2 due to both qGRH-4 and qGRH-2
was noted because there has been no report on GRH resistance gene on chromosome
2. qGRH-4 was located near the gene resistant to green leafhopper
Nephotettix virescens Distant (Sebastian et al. 1995). Development
of isogenic lines for qGRH-4 and qGRH-2 is necessary to
precisely analyze the genetic basis of GRH resistance of IR20965-26-1-2.
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:
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.
Sebastian, L. S., R. Ikeda, N. Huang, T. Imbe, W. R. Coffman and S. R.
McCouch, 1995. Molecular mapping of resistance genes to rice tungro spherical
virus and green leafhopper in rice. Phytopathology 86: 25-30.
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 (Nephotettix cincticeps
Uhler) in rice cultivar DV85 using near isogenic lines. Sci. Bull. Fac.
Agr. Kyushu Univ. 52: 169-175. (Japanese with English summary)