Mapping and pyramiding of two major genes for resistance to the brown planthopper (Nilaparvata lugens [Stål]) in the rice cultivar ADR52

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most serious and destructive pests of rice, and can be found throughout the rice-growing areas of Asia. To date, more than 24 major BPH-resistance genes have been reported in several Oryza sativa ssp. indica cultivars and wild relatives. Here, we report the genetic basis of the high level of BPH resistance derived from an Indian rice cultivar, ADR52, which was previously identified as resistant to the whitebacked planthopper (Sogatella furcifera [Horváth]). An F2 population derived from a cross between ADR52 and a susceptible cultivar, Taichung 65 (T65), was used for quantitative trait locus (QTL) analysis. Antibiosis testing showed that multiple loci controlled the high level of BPH resistance in this F2 population. Further linkage analysis using backcross populations resulted in the identification of BPH-resistance (antibiosis) gene loci from ADR52. BPH25 co-segregated with marker S00310 on the distal end of the short arm of chromosome 6, and BPH26 co-segregated with marker RM5479 on the long arm of chromosome 12. To characterize the virulence of the most recently migrated BPH strain in Japan, preliminary near-isogenic lines (pre-NILs) and a preliminary pyramided line (pre-PYL) carrying BPH25 and BPH26 were evaluated. Although both pre-NILs were susceptible to the virulent BPH strain, the pre-PYL exhibited a high level of resistance. The pyramiding of resistance genes is therefore likely to be effective for increasing the durability of resistance against the new virulent BPH strain in Japan

Anther culture in rice proportionally rescues microspores according to gametophytic gene effect and enhances genetic study of hybrid sterility

BackgroundTo investigate plant hybrid sterility, we studied interspecific hybrids of two cultivated rice species, Asian rice (Oryza sativa) and African rice (O. glaberrima). Male gametes of these hybrids display complete sterility owing to a dozen of hybrid sterility loci, termed HS loci, but this complicated genetic system remains poorly understood.ResultsMicrospores from these interspecific hybrids form sterile pollen but are viable at the immature stage. Application of the anther culture (AC) method caused these immature microspores to induce callus. The segregation distortion of 11 among 13 known HS loci was assessed in the callus population. Using many individual calli, fine mapping of the HS loci was attempted based on heterozygotes produced from chromosome segment substitution lines (CSSLs). Transmission ratio distortion (TRD) from microspores was detected at 6 of 11 HS loci in the callus population. The fine mapping of S-1 and S-19 loci using CSSLs revealed precise distances of markers from the positions of HS loci exhibiting excessive TRD.ConclusionsWe demonstrated that AC to generate callus populations derived from immature microspores is a useful methodology for genetic study. The callus population facilitated detection of TRD at multiple HS loci and dramatically shortened the process for mapping hybrid sterility genes

Cytogenetics of Ditelosomic Alien Addition Lines in rice (Oryza sativa L.) Each Carrying an Extra Pair of Telocentric Chromosomes of O. punctata Kotschy

Ditelnsomic alien addition lines ( UtAALs : 2n=2x+2t) of rice each carrying a pair of telocentric chromosomes of Oryza punctata were isolated aL low frequencies (2.5-11 .1%) from the progenies or respective monotelosomic alien addition lines ( MtAALs : 2n=2x + 1t) 7, 11 and one unidentified MtAAL. During the meiosis, the alien telocentric chromosomes of three DtAALs completely paired at the pachytene and usually separated to each daughter cell at anaphase I, giving rise to viable gametes with an alien telocentric chromosome at high frequencies. These DtAALs were characterized by stable transmission of the alien telocentric chromosome in the progenies. The transmission rates of the alien chromosome were considerably high in the DtAALs, and most plants of their self-pollinated progeny carried at least one alien telocentric chromosome. The pollen and seed fertility were different among three DtAALs. DtAAL 11 carrying a short telocentric chromosome of O. punctata showed high pollen and seed fertility similar to the disomies. The DtAALs showed relatively stable transmission of alien telocentric chromosome(s), where gametes with an extra telocentric chromosome are functional in both female and male germ cells. These suggest that small chromosome fragment with functional centromere, that is a telocentric chromosome, can be transmitted to the progenies and be stable in the next generation. High transmission rates of the alien telocentric chromosome in these DtAALs assure the efficient changes in genetic background of any recipient cultivars by backcrossing