Ryoichi IKEDA and Duncan A. VAUGHAN
International Rice Research Institute, P.O. Box 933, Manila, Philippines
The brown planthopper (BPH) is one of the most serious rice pests in tropical and temperate Asia. Since Athwal et al. (1971) identified Bph-1 and bph-2 genes in Mudgo and ASD 7, respectively, nine resistance genes have been reported to date. Four biotypes of BPH are known. Biotypes 1 is widely distributed in East and Southeast Asia; biotype 2 originated in Philippines after widescale cultivation of varieties with Bph-1 gene and biotype 3 was produced in laboratories in both Japan and the Philippines. Biotype 4 is found only in South Asia. The varieties have been classified into three groups in the Philippines and Japan as follows: (1) Bph-1 group; resistant to biotypes 1 and 3 but susceptible to biotype 2, (2) bph-2 group; resistant to biotypes 1 and 2 but susceptible to biotype 3, and (3) the group with Bph-3, bph-4, bph-8 or Bph-9; resistant to all three biotypes. The other three genes, bph-5, Bph-6 and bph-7 convey resistance to biotype 4 only.
1. Cultivated varieties
In Japan, Kaneda et al. (1981) reported the results of screening about 3,300 cultivars and breeding lines from different regions of the world. Most of the resistant traditional cultivars came from Kerala, Tamil Nadu and Andhra Pradesh states of southern India and Sri Lanka. Based on the reaction patterns of these varieties to different biotypes the proportion of resistance genes found in Sri Lankan traditional varieties was different from those in India. About 60 per cent of the Sri Lankan cultivars were found to possess the bph-2, in contrast only 10 per cent of the Indian cultivars tested had this gene. Heinrichs et al. (1985) also listed the resistant varieties with the reaction to three biotypes at IRRI, the Philippines, and the results are similar to those of Kaneda et al. (1981). Out of 272 resistant varieties, 193 (717o) were from Sri Lanka with most varieties showing resistance to 2 biotypes and 62 (237o) were from India with most varieties showing resistance to all 3 biotypes (Table 1). Khush (1977) also reported that most BPH resistant varieties came from Sri Lanka and neighboring states of India.
South India and Sri Lanka may be considered a secondary center for rice diversity with a wealth of wild species and rice cultivation dating back to more than several thousand years. Irrigation tanks which may have permitted double cropping of rice were built by the fifth century AD in Sri Lanka (Watabe 1990). Under intensive cultivation BPH biotypes and resistant cultivars evolved. The Palk Strait between Sri Lanka and India, although narrow, acts, as a barrier to biological movement. There are many differences between the flora of Sri Lanka and Tamil Nadu. Currently Sri Lankan breeders are using sources of resistance to BPH from India, such as Ptb33, since Sri Lankan traditional varieties are now susceptible to the BPH diversity of Sri Lanka (D. Senadhira, pers. comm.).
Table 1. Distribution of BPH resistant varieties in India and Sri Lanka =============================================================================== Reactions to three biotypes2) Origin of Country Location of test1) ======================================= RRR RSR RRS Total =============================================================================== India NARC 20 12 5 37 (54%) (32%) (14%) IRRI 32 25 5 62 (52%) (40%) (8%) Sri Lanka NARC 15 24 49 88 (17%) (27%) (56%) IRRI 52 57 84 193 (27%) (29.5%) (43.5%) =============================================================================== 1) NARC, IRRI; cited from Kaneda et al. (1981), Heinrichs et al. (1985), respectively, 2) reactions to biotypes 1, 2, and 3.
2. Wild relatives of rice
Resistance to each BPH biotype is encountered about 30 times more frequently in populations of wild rices than in cultivated varieties. However, the resistance to all three biotypes in wild relatives was found to be even higher; more than 50 times the occurrence in traditional varieties (IRRI, 1991) (Table 2). Broad resistance to BPH biotypes is thus more common in wild than in the cultivated rices.
Heinrichs et al. (1985) listed 12 species and natural species hybrids resistant to BPH. Five species, O. nivara, O. ridleyi, O. officinalis, O. minuta, O. australiensis, and natural hybrids are distributed in Asia or tropical Australia. This may be considered sympatric resistance since the distribution of these species matches the distribution of the BPH. However, the other species of Africa and tropical America, O. brachyantha, O. barthii, O. punctata, O. glumaepatula, O. latifolia, O. alta, and African strains of O. eichingeri exhibit allopatric resistance (Table 3). In particular, the BPH resistance in populations of O. latifolia showed differential reaction patterns as five accessions were resistant to all three biotypes, four exhibited the reaction pattern associated with Bph-1, four showed the reaction pattern associated with bph-2. This reveals that BPH is compatible with O. latifolia and this resistance is not a species characteristic (Table 3).
When sources of resistance to a stress can be found both where the stress is present and where it is absent, it may be worthwhile analyzing gene differences from both sources. Genes arising from coevolution in a gene for gene manner can be overcome by a pathogen. A stress tolerance which arises independently of the stress may be more difficult to breakdown (Harris 1975).
Table 2. Screening of varieties and wild relatives for resistance to BPH at IRRI 1991 (from database for GEU program) =============================================================================== Variety Wild relatives =========================== ============================ Total Resistant (%) Total Resistant (%) =============================================================================== Biotype1) 1 44,335 682 (1.5) 723 302 (41.8) 2 10,053 187 (1.9) 724 242 (33.4) 3 13,021 236 (1.8) 730 272 (37.3) Reaction patterns2) 7,022 579 RRR 48 (0.7) 219 (37.8) RSR (Bph-1) 121 (1.7) 14 (2.4) RRS (bph-2) 83 (1.1) 3 (0.5) =============================================================================== 1)reactions to each biotype 2)reactions to 3 biotypes (biotypes 1, 2 and 3)
Table 3. Wild rice species resistant to BPH (cited from Heinrichs et al. 1985) =============================================================================== Species complex Genome Resistant to BPH Taxa group ========================================= RRR RSR RRS =============================================================================== O. branchyantha FF 2 O. sativa complex O. nivara AA 9 1 Natural hybrids AA 3 1 O. barthii AA 2 1 O. glumaepatula AA 1 O. ridleyi complex O. ridleyi tetraploid 2 O. officinalis complex O. officinalis CC 37 2 O. eichingeri CC 5 2 O. minata BBCC 28 O. punctata BB,BBCC 7 5 O. latifolia CCDD 5 4 4 O. alta CCDD 1 O. australiensis EE 4 ===============================================================================
Athwal, D. S., M. D. Pathak, E. H. Bacalangco and C. D. Pura, 1971. Genetics of resistance to brown planthoppers and green leafhoppers in Oryza sativa L. Crop Sci., 11: 747-750.
Harris, M. K., 1975. Allopatric resistance: searching for sources of insect resistance for use in agriculture. Environ. Entom. 4: 661-669.
Heinrichs, E.A., F.G. Medrano and H.R. Rapusas, 1985. Genetic evaluation for insect resistance in rice. pp. 356, IRRI, Los Banos, Lagna, Philippines.
IRRI 1991. Database for GEU program at IRRI.
Kaneda, C., K. Ito and R. Ikeda, 1981. Screening of rice cultivars for resistance to the brown planthopper, Nilaparvata lugens Stal., by three biotypes. Jpn. J. Breed. 31(2): 141-151.
Khush, G. S., 1977. Disease and insect resistance in rice. Advances in Agronomy 29: 265-341.
Watabe, T., 1990. The roots of the rice we eat. Tracing the history of rice cultivation. pp. 219, PHP Res. Inst. Tokyo, Japan (in Japanese).