QTL Analysis For Rice Stripe Disease Resistance

Rice stripe disease transmitted by small brown planthopper (Laodelphax striatellus Fall.) is one of the most serious viral diseases in East Asia. The virus is readily transmitted to test plants by the planthopper, Laodelphax striatellus, but is difficult to transmit mechanically. The virus passes through a high percentage of eggs to progeny, about 90% in L. striatellus. RSV occurs naturally in rice, maize, wheat, oat, foxtail millet and wild grasses The virus is reported to infect 37 species of the family Gramineae.The disease was first recognized in the early 1900s in central Japan, where severe damage was caused to rice crops. Since the 1950s the extension of early planting favoured the occurrence of the disease in Japan and during the 1960s and 1970s about 200,000 ha of rice was affected each year. In Korea, the disease affected 40% of rice hills in 1965. Stripe disease incidence in Taiwan was most severe around 1970: 1045 ha were affected in 1973. Stripe disease is broadly prevalent all over the rice-growing areas in China and the ex-USSR.The disease is severely epidemic in most rice growing areas where the main cultivars are susceptible or moderately susceptible to rice stripe virus.In this research, a recombinant inbred lines (RILs) mapping population including 81 lines derived from a cross of Kinmaze (japonica)/DV85(indica) by the single seed descent method was used to detect quantitative trait loci (QTL) conferring resistance to rice stripe virus. The reaction of the two parents and 81 RILs to rice stripe virus were investigated by inoculating seedlings with viruliferous small brown planthopper insects, and scored by the disease rate index. The quantitative trait loci for rice stripe disease resistance were analyzed by QTL Cartographer software. Three QTL controlling RSV resistance were detected on chromosomes 1,7 and 11, respectively. Individual QTL accounted for 19.8% ~ 30.9% of the phenotypic variance in the RILs population. The direction of the additive gene effects at two loci qStv7 and qStvll coincided with that predicted by phenotypes of the parents. At these two loci, the DV85 alleles increased the resistance to RSV, while at qStvll, the Kinmaze alleles increased the resistance to RSV.Another mapping population, the backcross recombinant inbred lines(BIL) derives from a cross of Nipponbare/Kasalath//Nipponbare by the single seed descent method, was used to detect quantitative trait loci (QTL) conferring resistance to rice stripe virus, too. This population was inoculated by both manual method in lab and natural method in field. By manual inoculation, two QTL controlling RSV resistance were detected on chromosomes 7 and 11, respectively. By natural inoculation, one QTL was detected on the same location as above on chromosome 11. The results indicated that this QTL on chromosome 11 was important to control the resistance to RSV.These QTL should be useful in breeding rice varieties resistant to RSV in marker-assisted selection (MAS) program.