| The brown planthopper (BPH), Nilaparvata lugens (Stal), is one of the most serious insect pests of rice (Oryza sativa L.) in Asian rice growing areas. It not only causes direct damage by sucking plant sap but also transmits several viral diseases such as rice grassy stunt and rugged stunt. BPH has been called a pest of the green revolution because of the adoption pf modern agricultural practices (e.g., flooding fields, increased use of nitrogenous fertilizer, and the use of high yielding varieties). Prior to 1970, the rice BPH was not regarded as a pest of tropical rice and received only a brief mention in an illustrated field guide to rice pests in the Philippines. Since 1970s, however, this monophagous planthopper has achieved major pest status, causing massive losses in rice production throughout Asia.Protection against BPH pest insects has depended mostly on insecticides in the past. However, one common cause of insect pest outbreaks is the resurgence of insect pest population in response to inecticide application. One of the primary factors responsible for pest resurgence has long been believed to be the elimination of natural enemies as a result of inecticide application. Another implicated resurgence mechanism is the enhancement of insect fecundity by chemical stimulation, and researchers have demonstrated that certain chemicals, such as decamethrin, methyl parathion and diazinon, could stimulate reproduction of planthopper females.Outbreaks of BPH promoted the international Rice Research Institute (IRRI) to initiate a breeding program for the development of resistant varieties of rice. To slow down the evolution of BPH population, several approaches have been proposed over the years, such as rotating different cultivars, planting multiple resistant lines within the same field, and combing different resistance genes within the same cultivar. It also has been proposed that moderate and/or polygenic resistance to insect pests, including BPH, should provide more durable resistance than single major genes. Therefore, new genes and quantitive trait locus (QTL) for BPH resistance must be constantly identified and incorporated into breeding program.In this study, SSR mapping and marker-assisted selection of a brown planthopper resistance gene bph2 in ASD7. Fine mapping of Bph3 in Rathu Heenati and analysis ofQTL for resistance to BPH in an indica rice Co1.5 Thailand were the other two main research topics in this study. The results were as folio wings:(1) In the study reported here, ASD7 harboring a BPH resistance gene bph2 was crossed to a susceptible cultivar C418, a japonica restorer line. A F2 segregating population composed of 134 plants was constructed from the cross between ASD7 and C418, and each F2 plant was selfed to obtain F2:3 line. BPH resistance was evaluated using 134 F2:3 lines, and the genotype of each F2 plant was inferred from the phenotype of corresponding F2.3 line. SSR assay and linkage analysis were carried out to detect bph2. As a result, the resistant gene bph2 in ASD7 was successfully mapped between RM7102 and RM463 on the long arm of chromosome 12, with distances of 7.6cM and 7.2 cM, respectively. Meanwhile, both phenotypic selection and marker assisted selection (MAS) were conducted in the BC1F1 and BC2F1 populations. Selection efficiencies of RM7102 and RM463 were determined to be 89.9% and 91.2% respectively. It would be very beneficial for BPH resistance improvement by using MAS of this gene.(2) A Sri Lankan indica rice (Otyza sativa L.) cultivar Rathu Heenati harboring a brown planthopper (BPH) (Nilaparvata lugens Stal) resistance gene Bph3, showed resistanqe to all the four biotypes of BPH. But Bph3 has not been mapped with molecular markers to date. In this study, we constructed a linkage map to determine the locus for BPH resistance gene, using an F2 population from a cross between 'Rathu Heenati' and a susceptible cultivar '02428'. Insect resistance was evaluated using 156 F23 lines and the genotype of each F2 plant was inferred from the phenotype of corresponding F2:3 lines. The e...
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