Rice breeding for brown planthopper resistance with induced mutations

Brown planthopper, Nilaparvata lugens (Stal), has become the most serious pest of rice in Asia. Damage by this insect caused severe yield losses in several countries. In Thailand no severe damage from BPH was noticed prior to 1974. Up to the present, the recommended RD 9, RD 21 and RD 23 rice varieties resistant to BPH are popular among rice growers. Mutation breeding for BPH resistance in rice began in 1979 under a research contract between the Rice Research Institute, Department of Agriculture, Thailand and the International Atomic Energy Agency, Vienna, Austria. Seeds of RD 7 were treated with either 20 krads of gamma rays or 0.2 percent solution of the chemical EMS in an attempt to induce BPH resistance in this variety. Selections for BPH resistance are started from M2 to M5 generation. After the BPH susceptible lines were discarded, good grain qualities with long slender clear grain are simultaneously selected along with the BPH resistance character in M5 generation. Mutant lines with BPH resistance are further selected. In the 1983 wet season, 32 promising mutant lines with recommended RD 7 and RD 23 check varieties were put in two Intra Station Non-sensitive Yield Trials (4-row with 3 replications) at Suphan Buri Rice Experiment Station (SPR). Two of the mutant lines (promising lines), RD 7'79-G1Cs-10-6-1-2 and RD 7'79-G1Cs-10-6-1-3 ranked first and second in average yields but not significantly outyielded the original rice variety RD 7 and other recommended rice variety checks. Two outstanding yields were 4.98 and 4.94 ton/ha. (rank 1 and 2) as the RD 23, the resistance check variety and RD 7, the original variety was 4.84 and 4.53 ton/ha. respectively. Six hundred and 69 mutant lines (the M4 generation seeds from M3 generation plants) were rescreened again in the screenhouse at Bangkhen Rice Experiment Station in order to confirm their resistance to BPH. From these, the 397 resistant to BPH M4 plants from 496 lines were transplanted and harvested in the 1983 wet season. Seeds in M5 generation will also be tested for blast resistance in Upland Short Row in the 1984 wet season; the original RD 7 is not resistant to blast.