Transmission of Rice Stripe Virus by Laodelphax striatellus (Fallén)

Movement of the stripe virus in rice leaf was intercepted or delayed by pre-treatments known to affect the function of phloem, viz., with chemicals such as sodium azide, monoiodoacetic acid, dinitrophenol, chloroform and alcohol, cooling or steam-heating at the portion about 2cm below the area to be fed by viruliferous smaller brown planthoppers. Results of severing tests showed that the virus moved downward in the inoculated leaf at a rate of 25 to 30cm per hour. The virus given off by brown planthopper was recovered at a distance of 5 to 7cm from the site of feeding, by using Unkanodes albifascia, hopper of outstanding compatibility with stripe virus. Rate of virus movement was enhanced by increase in number of hoppers for inoculation and by time for feeding longer than 1 hour. Treatments such as cutting off roots, folding leaf blades or exposing to low temperature (15C), effected adversely. Movement in highly resistant varieties was remarkably hindered as compared with susceptible varieties.Initial symptoms usually appeared on the upper leaf next but one from the inoculated leaf. The portions where disease symptoms developed coincided with the tissue in which cell division was taking place at the time of inoculation. The presence of virus was verified by hemagglutination test in the tissues of top extending from the leaf sheath of next upper leaf and leaf blade next but one from the inoculated leaf to the uppermost leaf primordium, and in root. In the leaves which had been expanded at the time of inoculation there was no evidence of virus multiplication. These results suggest that the stripe virus injected by the hopper passes through phloem, without multiplying at the feeding site, and reach younger tissues feasible for multiplication.