Miyazaki Agric. Experiment Station, Sadohara, Miyazaki-gun, 880-02 Japan
The green rice leaf hopper (Nephotetti x cincticeps Uhler) became an important pest of rice in Japan after the Second World War. Breeding for resistance to this insect has been carried out to develop resistant strains. We are also investigating the inheritance of resistance to this insect.
Two new biotypes of this insect infesting resistant strains were isolated in our nursery. The ordinary unselected colony is called biotype 1 in this paper. Biotype 2 infests Aichi 42 (Aichi 42 colony), and biotype 3 infests Saikai 182 (Saikai 182 colony). The reactions of resistant strains to these biotypes are examined by the antibiosis test. A seedling is inoculated with five second- instar nymphs of the leafhopper in a test tube 18 cm long, 1.8 cm in diameter), watered and stoppered with a cotton ball. Mortality of the insects is recorded 4 days after inoculation. Five replications were made.
The reactions of rice strains to the three biotypes appeared to be specific or vertical. Norin-PL2, Kanto PL6 and Aichi 42 showed similar reactions although they had different donors for resistance (Table 1). They were resistant to biotypes 1 and 3, but were susceptible to biotype 2. In contrast, Saikai 182 was resistant to biotypes 1 and 2 and susceptible to biotype Norin-PL5 was resistant to all the three biotypes. It is known that Norin-PL2 has a resistance gene Grh-1 and Norin-PL5 has Grh-2 (RGN 1, p. 45; Kobayashi et al. 1980). We reported further that Norin-PL5 has two dominant resistance genes, Grh-2 and another unknown gene (Takita and Nishiyama 1989).
Crosses were made between Kanto PL6, Aichi 42 and Saikai 182, and each of the F2 seedlings were tested in a test tube for insect mortality 7 days after
Table 1. Reactions of rice strains to 3 biotypes of green rice leafhoppers and their assumed resistance genes
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Mortality of leafhoppers (%)
Source of ================================ Resistance
Rice strain Biotype 1 Biotype 2 Biotype 3 gene
resistance (Unselected (Aichi 42 (Saikai 182 assumed
colony0 colony) colony)
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Norin-PL2 Pe-bi-hun 52% 4 80 Grh-1
Kanto-PL6 Tadukan 80 4 80 "
Aichi 42 Rantaj-emas 2 80 0 92 "
Saikai 182 C203-1 72 72 0 Grh-2
Norin-PL5 C203-1 100 100 100 Grh-1& amp;Grh-2
Nishihomare 0 0 0 none
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Table 2. Reactions of F2 populations to green rice leafhopper (biotype 1)
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No. of F2 plants
Cross ===========================Ratio X2 from 15:1
Resistanta Susceptibleb
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Saikai 182XAichi 42 98 9 15:1 0.85(P>0.25)
Saikai 182XKanto PL6 98 7 15:1 0.03(P>0.75)
Aichi 42XKanto PL6 105 0 1:0
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a-(R), mortality>40%; b-(S), mortality<20% (7 days after inoculation).
inoculation, using insects of biotype 1 (Table 2). Two crosses, Saikai 182 X
Aichi 42 and Saikai 182 X Kanto PL6, both showed a 15R: 1S ratio, while the
F2 plants from Aichi 42XKanto PL6 were all resistant suggesting that the both
parents had the same resistance gene. It may be assumed tentatively that
Aichi 42 and Kanto PL6 have Grh-1 similary as has Norin-PL2, while Saikai 182
has Grh-2. The resistance of Saikai 182 to biotypes 1 and 2 suggests that
Grh-2 confers resistances to biotypes 1 and 2. Gene Grh-1 in Norin-PL2,
Kanto PL6 and Aichi 42 confers resistances to biotypes 1 and 3.It is known that Salkai 182 was derived froni North-PL5, which has Grh-2 and another resistance gene. If it is assumed that Norin-PL5 has both Grh-1 and Grh-2, its resistance to biotypes 1, 2 and 3 can be explained. Further studies are needed to verify this assumption.
References
Kobayashi, A., C. Kaneda, R. Ikeda and H. Ikehashi, 1980. Inheritance of resistance to green rice leafhopper, Nephotetti x cincticeps, in rice. Jpn. J. Breed. 30, Suppl. 1: 56-57. (in Japanese)
Takita, T. and H. Nishiyama, 1989. Selection of biotypes of green rice leafhopper and genetic analysis for the resistance in rice. Bull. Kyushu Natl. Agric. Exp. Station 25: 251-259.