Genetic Analysis For The Resistance To Small Brown Planthopper(Laodelphax Striatellus Fallen) In Two Rice Varieties

Rice (Oryza sativa L.) is the staple food for more than 50% of the world’s population, although insect pests are the major biotic constraints to production of this crop. The Small brown planthoper, Laodelphax striatellus Fallen (Homoptera:Delphacide), is one of the most destructive and wide spread insect pests found throughout the temperate rice-growing regions such as China, Japan and Korea. The population of Laodelphax striatellus Fallen has increased steadily due to alteration of the cropping system and infested South East China. The dults and nymphs of Laodelphax striatellus Fallen suck rice sap causing yellowing of leaves, wilting and eventually death resulting in yield loss.The pest also transmits viral diseases such as Rice stripe virus, and rice black streaked dwarf virus causing further yield loss. Chemicals have mostly been used to control Laodelphax striatellus Fallen, although it has developed resistance to most of them. Use of these chemicals has also resulted into death of natural enemies and pollution of the environment leading to the resurgence of the pest. Development of resistant varieties is the most effective and economical way in controlling this pest. The feeding behavoiur of the pest was evaluated on two rice varieties bearing resistance genes derived from three basic resistance mechanisms:antibiosis, antixenosis and tolerance by identifying the resistance genes in rice varieties with the help of the QTL1. A set of F2 and BC1 population derived from the cross between 02428 and Rathu Heenati were used to investigate the small brown planthopper resistance loci. Using the F2 population, three QTLs for antixenosis resistance were located on chromosome 2,5 and 6, respectively accounting for 30.75% of the phenotypic variance. The QTL on chromosome 2 was also identified in BC1 population. Three QTLs for antibiosis against the pest were detected on chromosome 8,9 and 12, respectively in F2 population. qSBPH5-c explaining 7.21% of phenotypic variance for antibiosis against the insect was identified on chromosome 5 using BC1 population. A major QTL qSBPH12-al explained about 40% of phenotypic variance and a minor QTL (qSBPH4-a) were detected by SSST method using both the F2 and BC1 population. The QTLs identified in present study will be useful for mark assisted selection for SBPH resistance in rice.2. The Japonica rice 02428 and the indica rice Changhui891, was used to detect quantitative trait loci (QTLs) for the resistance to SBPH. Modified seedling screening test (MSST), along with antixenosis test and antibiosis test were applied to evaluate the resistance response of the two parents and 149 plant F2 to the insect and composite interval mapping (CIM) was used for QTL analysis. When the resistance was measured by MSST method, two QTLs conferring resistance to Small brown planthopper were mapped on chromosome 6 and chromosome 7 namely qSBPH6-a and qSBPH7-a, with log of odds (LOD) scores 2.61 and 2.91, respectively; and two QTLs explained 8.75% and 13.1% of the phenotypic variance in this population, respectively. Two QTLs, namely qSBPHI-c and qSBPH2-c, expressing antibiosis to SBPH were mapped on chromosomes 1 and 2, respectively, explaining 30.16% of the total phenotypic variance.