High-Resolution Mapping Of The Brown Planthopper Resistance Gene BPH22(T) In Rice

Nilaparvata lugens Stal, the brown planthopper (BPH), is one of the most destructive phloem-feeding insect pests of rice (Oryza sativa L.) throughout Asia. It attaches by preference to the stem, from where it penetrates the phloem through its stylet. BPH feeding interferes with the translocation of assimilate, thereby damaging plant growth and development. Where a large number of BPH individuals feed on a single plant, a common outcome is leaf desiccation and stem wilting, a condition called hopper-burn. BPH is also a carrier of two viruses, one responsible for the disease rice grassy stunt, and the other rugged stunt. Chemical control of BPH is commonly practiced, but is both costly and harmful to environment. The use of genetically resistant cultivars has proven to be a more economical, efficient and environmentally friendly means to control this pest.Non-durability of many of the major resistance genes due to changes in the pest biotype remains a problem. The frequency damaged on rice production by BPH infestation, has driven the search for new sources of genetic resistance. It has been suggested that quantitative resistance may,be more durable than that determined by major genes, but these genes are more difficult to handle in a breeding program. Fine mapping is the key step for mapping based cloning, and the development of resistance gene closed linked molecular marks would provid the useful tools for the application of resistance gene.The identification and cloning of insect resistance is not only helpful for elucidating the molecular mechanism, and also can speed up the application in breeding program. Even a gene has been fine mapped, but there would still be a number of candidate genes. However, if the mechanism of the gene has been clear, it would be able to provide a basis for cloning of the target gene and also can improve the efficiency in production.In this study, we evaluated the feeding behavior of BPHs on rice varieties Balamawee, Kaharamana and Pokkali with the same BPH resistant gene Bph9according to the previous report, and accomplished the genetic analysis and high-resolution mapping of a novel brown planthopper resistance gene Bph22(t).1. The Feeding Behaviors of Brown Planthopper on Resistance Rice CultivarsIn this study, we evaluated the resistance mechanism of three rice cultivars Balamawee, Kaharamana and Pokkali containing the same dominant brown planthopper resistance gene Bph9based on the understanding of the mechanisms of plant resistance to herbivorous insects:antibiosis, nonpreference and tolerance. It was shown that Balamawee was a typical antibiosis and nonpreference cultivar, while Kaharamana and Pokkali were tolerance cultivar. Although it was previously reported that Balamawee, Kaharamana and Pokkali contained the same dominant brown planthopper resistance gene Bph9, the feeding behavior of brown planthopper on Balamawee and Kaharamana as well as Pokkali were significantly different.2. Genetic analysis and preliminary mapping of a dominant brown planthopper (BPH) Nilaparvata lugens Stal resistance Bph22(t)in riceSri Lanka rice cultivar Balamawee showed broad-spectrum resistance to BPH biotype1,2and3in East and Southeast Asia. Analysis of the mechanism of resistance to brown planthopper showed that Balamawee was a typical antibiosis and nonpreference cultivar. Genetic analysis of gene controlling the resistance to brown planthopper in Balamawee via F2segregating population showed that the resistance gene in Balamawee was a dominant gene. It was mapping between SSR marker RM471and RM5742on the long arm of chromosome4, with the distance of12.0cM and4.7cM to each marker respectively. This interval of chromosome4had not been reported containing brown planthopper resistance gene previously. The resistance gene was a novel brown planthopper resistance gene designated as Bph22(t).3.Fine mapping of a brown planthopper (BPH)Nilaparvata lugens Stal resistance gene, Bph22(t)in riceIn order to fine-map the gene Bph22(t), a F2segregation population with8761individuals derived from a cross of Balamawee/02428was used. Based on the initial mapping information, the polymorphism analysis of public SSR primers between RM471and RM5742was made, and sevaral SSR markers and InDel markers were newly developed according to the publicly available rice genomic sequences. Recombination analysis using the existing and newly developed markers of all individuals in F2segregation population were carried out. The results of reconbination analysis combined with phenotype identification indicated that Bph22(t)was delimited in an63Kb interval between two InDel marker Q52and Q20.