Wild relatives are sources of genes for resistance to diseases and insect
pests. The Nephotettix cincticeps Uhler (Green rice leafhopper:
GRH) is one of the serious insect pests of rice in temperate Asia. An
accession of wild relative, Oryza rufipogon Griff. (W1962) was
found to be highly resistant to GRH by antibiosis test. In the present
study, we found a new resistance gene for GRH introgressed from O.
The introgression lines derived from a cross between a resistant accession
of O. rufipogon (W1962) and a susceptible Japonica variety Taichung
65 were used for the analysis. To evaluate nymph mortality as GRH resistance,
leaf blades of 98 BC4F2 plants were excised and
infested with 7-10 first- or second-instar nymphs. The insect population
was collected in Fukuoka Prefecture in 1991, and was maintained by continuously
rearing at 25C and 16h light: 8h dark condition. The nymph mortality in
BC4F2 individuals showed a discrete distribution,
segregating into 69 resistant and 29 susceptible plants. The segregation
ratio fitted to a 3:1 ratio (chi2=1.35), indicating that the
GRH resistance was controlled by a single dominant gene. To determine
the chromosomal location of the resistance gene, BC3F1
plants were analyzed using 767 simple sequence repeats (SSR) markers (McCouch
et al. 2002) by bulked segregant analysis. The linkage between
the resistance gene and one SSR marker, RM4154 was detected. Further
SSR analysis using BC4F2 individuals revealed that
the resistance gene was
located between RM1615 and RM6845 and tightly
linked to RM3754 and RM3761 on the distal region in long
arm of chromosome 8 (Fig. 1). So far, five genes for resistance to GRH
have been mapped on rice chromosomes using RFLP markers, Grh1 on
chromosome 5 (Tamura et al. 1999a), Grh2 and Grh4
on chromosomes 11 and 3, respectively (Fukuta et al. 1998; Yazawa
et al. 1998), Grh3(t) on chromosome 6 (Saka et al.
1997), and Grh(t) on chromosome 4 (Tamura et al. 1999b).
There have been no genes for resistance to GRH on chromosome 8. Therefore,
we designated the new resistance gene as Grh5 (Green rice leafhopper
resistance 5). Nearly isogenic line (NIL) for Grh5 was selected
in BC4F2 population. The nymph mortality in the
NIL was more than 90%. It was higher than those of varieties each carrying
single GRH resistance genes reported previously (unpublished data). Thus,
Grh5 introgressed from O. rufipogon is a favorable gene
resource for rice improvement.
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resistance to green rice leafhopper (Nephotettix cincticeps Uhler)
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