Masahiro Hirae

Detection and diagnosis of rice-infecting viruses

Rice-infecting viruses have caused serious damage to rice production in Asian, American, and African countries, where about 30 rice viruses and diseases have been reported. To control these diseases, developing accurate, quick methods to detect and diagnose the viruses in the host plants and any insect vectors of the viruses is very important. Based on an antigen–antibody reaction, serological methods such as latex agglutination reaction and enzyme-linked immunosorbent assay have advanced to detect viral particles or major proteins derived from viruses. They aid in forecasting disease and surveying disease spread and are widely used for virus detection at plant protection stations and research laboratories. From the early 2000s, based on sequence information for the target virus, several other methods such as reverse transcription-polymerase chain reaction (RT-PCR) and reverse transcription-loop-mediated isothermal amplification have been developed that are sensitive, rapid, and able to differentiate closely related viruses. Recent techniques such as real-time RT-PCR can be used to quantify the pathogen in target samples and monitor population dynamics of a virus, and metagenomic analyses using next-generation sequencing and microarrays show potential for use in the diagnosis of rice diseases.

Quantitative analysis of Rice stripe virus in a transovarial transmission cycle during the development and reproduction of its vector, Laodelphax striatellus

The amount of Rice stripe virus (RSV) maintained through transovarial transmission was analyzed during the development and reproduction of its vector, Laodelphax striatellus. Reverse transcription quantitative PCR analysis was used to quantify RNA expressed from the RSV coat protein (CP) gene as an estimate of RSV content in nymphs and adults of L. striatellus at various developmental stages. The 18S ribosome RNA gene of L. striatellus was chosen as the reference for calculating RSV CP expression using the comparative Ct method. Based on the CP transcript levels, the amount of RSV did not differ significantly throughout the nymphal stage or between adult females of different ages; however, RSV content tended to increase slightly as males became older. The average RSV content in males was 1.30–2.49 times that in females. The amount of RSV in L. striatellus adults was compared between generations. The RSV content of female adults did not differ significantly between the parent and progeny populations three of three different females. L. striatellus grown to adults on a susceptible cultivar and five RSV-resistant cultivars were compared to analyze whether the amount of RSV varied among cultivars. Although the amount of RSV in L. striatellus adults differed significantly among the six rice cultivars evaluated, the difference seemed independent of whether resistance genes were present. In addition, the percentage of viruliferous insects was similar among cultivars.