Rice black-streaked dwarf virus (RBSDV) disease become epidemic in Jiangsu and Zhejiang provinces. To screen resistant germplasms and discover new resistance genes/QTLs against RBSDV, we evaluated the resistance to RBSDV in 311 japonica varieties in field test. The results showed that no variety was immune to RBSDV. The disease rate of 24 main japonica varieties grown in Jiangsu province at present was 10.0%-29.0% and that of 71.5% varieties in 287 japonica varieties popularized in Jiangsu before was 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 contributed 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).

Small brown planthopper (SBPH) and rice stripe virus (RSV) disease transmitted by SBPH cause serious damage to rice (Oryza sativa L.) in China. In the present study, we screened 312 rice accessions for resistance to SBPH. The indica variety, N22, is highly resistant to SBPH. One hundred and eighty two recombinant inbred lines (RILs) derived from a cross of N22 and the highly susceptible variety, USSR5, were used for quantitative trait locus (QTL) analysis of resistances to SBPH and RSV. In a modified seedbox screening test, three QTLs for SBPH resistance, qSBPH2, qSBPH3 and qSBPH7.1, were mapped on chromosomes 2, 3 and 7, a total explaining 35.1% of the phenotypic variance. qSBPH7.2 and qSBPH11.2, conferring antibiosis against SBPH, were detected on chromosomes 7 and 11 and accounted for 20.7% of the total phenotypic variance. In addition, qSBPH5 and qSBPH7.3, expressing antixenosis to SBPH, were detected on chromosomes 5 and 7, explaining 23.9% of the phenotypic variance. qSBPH7.1, qSBPH7.2 and qSBPH7.3, located in the same region between RM234 and RM429 on chromosome 7, using three different phenotyping methods indicate that the locus or region plays a major role in conferring resistance to SBPH in N22. Moreover, three QTLs, qSTV4, qSTV11.1 and qSTV11.2, for RSV resistance were detected on chromosomes 4 and 11. qSTV11.1 and qSTV11.2 are located in the same region between RM287 and RM209 on chromosome 11. Molecular markers spanning these QTLs should be useful in the development of varieties with resistance to SBPH and RSV.

F(2) and BC(1) populations derived from the cross between 02428 / Rathu Heenati were used to investigate small brown planthopper (SBPH) resistance. Using the F(2) population, three QTLs for antixenosis against SBPH were located on chromosomes 2, 5 and 6, and accounted for 30.75% of the phenotypic variance; three QTLs for antibiosis against SBPH were detected on chromosomes 8, 9 and 12. qSBPH5-c explaining 7.21% of phenotypic variance for antibiosis was identified on chromosome 5 using the BC(1) population. A major QTL, qSBPH12-a1, explained about 40% of the phenotypic variance, and a minor QTL, qSBPH4-a, was detected by the SSST method in both the F(2) and BC(1) populations. The QTLs indentified in the present study will be useful for marker assisted selection of SBPH resistance in rice.