Resistant QTL Mapping Of Rice Stripe And Rice Black-Streaked Dwarf Disease Transmitted By Small Brown Planthopper

Rice black-streaked dwarf virus (RBSDV) disease become epidemic in Jiangsu, Zhejiang, Jiangxi and Fujian province. To screen resistant germplasm and discover new resistance genes/QTL against RBSDV, the resistance to RBSDV was evaluated in 311 japonica cultivars in field test. The results showed that no cultivar was immune to RBSDV. The disease rates of 24 main japonica cultivars from Jiangsu province and most cultivars in 287 japonica cultivars popularized in Jiangsu before were between 10.0% and 30.0%. Furthermore, quantitative trait loci (QTL) analysis was conducted by using 162 recombinant inbred lines (RILs), which derived from a cross between Guichao 2, a susceptible indica variety, and Koshihikari, a japonica variety with resistance to RBSDV. RBSDV resistances were evaluated using natural infection methods by scoring the disease rating. One putative QTL (qRBSDV3) controlling RBSDV resistance was mapped between the marker RM7 and RM5748 on chromosome 3, which explained 17.1% of the total phenotypic variation with LOD score of 5.4. The positive resistant effect came from Koshihikari. Further analysis revealed that the lines harboring the alleles of qRBSDV3 exhibited significantly increased resistance to RBSDV. The results should be very useful for breeding new RBSDV-resistant cultivars by marker-assisted selection (MAS).Rice stripe is one of the most economically devastating and widespread virus disease of rice in temperate rice-growing regions such as China, Japan and Korea. It has severely damaged rice production in growing areas of japonica cultivars, especially in Jiangsu Province, China. Rice stripe is transmitted by some species of planthoppers, of which, the small brown planthopper (SBPH, Laodelphax striatellus Fallen) is the major vector in rice fields. In recent years, along with the alteration of cropping system, the size of SBPH population has increased quickly. The virus-resistant cultivars widely used today only harbor Stvb-i gene on chromosome 11, which is introduced from "Modan", an indica cultivar from Pakistan. Because the occurrence of new virus strains may be able to nullify this gene and threaten these resistant varieties, we must diversify resistance sources to rice stripe. Therefore, it is absolutely necessary to screen the rice resources against rice stripe, investigate the genetic mechanism of new resistant genes, and apply these findings to breeding new virus-resistant cultivars.To discover new resistance genes to rice stripe, quantitative trait loci (QTL) analysis was conducted by using 162 recombinant inbred lines (RILs), which derived from a cross between Guichao 2, an indica variety with moderately resistance to rice stripe, and Koshihikari, a susceptible japonica variety. Rice stripe resistances were evaluated using both artificial inoculation and natural infection methods by scoring the ratio of the disease rating index. Three QTL controlling rice stripe resistance were detected by artificial inoculation and natural infection methods, which located on chromosomes 4(qStv4),9(qStv9) and 12(qStvl2), respectively. The qStv9 and qStv12 were repeatedly detected in the artificial inoculation test in 2006 and 2008. In the natural inoculation test, the qStv4 and qStv9 were detected in 2006, and the qStv12 was detected in 2008. Since the qStv9 and qStv12 explained 11.3%-32.1% of the resistance effect from Guichao 2 across two environments, they should be useful genetic resource in rice MAS breeding programs against rice stripe. Further analysis revealed that the lines harboring the alleles of qStv9 and qStv12 exhibited significantly increased resistance to rice stripe, implying the possibility of breeding new resistant varieties by pyramiding resistant QTL through marker-assisted selection.By quantitative trait loci (QTL) mapping and analysis of rice stripe resistance, three QTLs (qSTV3, qSTV7, qSTV11-i) were detected and located on chromosome 3, 7,11, respectively, using 71 recombinant inbred lines (RILs), which derived from a cross between IR24, a indica variety with moderate resistance to rice stripe, and Koshihikari, a susceptible japonica variety. The positive resistance effects at qSTV3, qSTV7 and qSTV11-i were all from IR24, the marker regions of qSTV3, qSTV7 and qSTV11-i coincided with IR24 segment in chromosome segment substitution lines (CSSLs) 17,39 and 62 with Asominori genetic background, respectively. In order to dissect these quantitative trait loci, we identify qSTV3, qSTV7 and qSTV11-i using three backcross advanced secondary population, Asominori/CSSL17 F2:3 (BC4F2:3), Asominori/CSSL39 F2:3 (BC4F2:3) and Asominori/CSSL62 F2:3 (BC4F2:3).The results indicated qSTV3 and qSTV11-i were detected in the advanced populations, but qSTV7 not. By Allelic Analysis, qSTVll-i and Stvb-i (a well known RSV resistant gene) were not allelic. Finally, the qSTVll-i was fine mapped to a 73.6kb region by using 5 new developed indel (insert and delete) markers and a F2:3 (BC4F2:3) population consisting of 2780 individuals. The markers used for fine mapping qSTV11-i will be convenient tools for marker-assisted selection of qSTV11-i in breeding programs of RSV-resistant rice.