Abstract：Rice stripe disease, caused by Rice stripe virus (RSV), has led to severe losses in many rice-cultured countries and regions. RSV is transmitted by the small brown planthopper (SBPHs), Laodelphax striatellus Fallén, in a persistent-propagative, and it also can be transmitted transovarially (vertically) by the small brown planthoppers to their offspring. In order to study the transovarial transmission characteristics of RSV by SBPH vectors, we tested viral infections in internal organs and in ovaries of SBPHs with RT-PCR assay and immunofluorescence for virus antigens. Our results showed that only 5.3% of SBPHs contained virus antigens in the ovaries with immunofluorescence for virus antigens, although the virus was detected by RT-PCR in 28.6% of SBPHs that had access to infected plants. Thus, the ovaries would form the transovarial transmission barrier for RSV, which might determine the efficiency of the transovarial transmission of RSV by SBPH vectors. We further investigated the sequential infection of RSV in the ovaries of SBPH vectors with immunofluorescence for virus antigens. Immunofluorescence studies revealed that RSV initially infected the oviduct, and then progressed to the follicular cells of ovarioles. RSV also could accumulate in the germarium and the nutritive cord of the ovary and in the blastodermal cells of the eggs after oviposition. All these results suggested that RSV might spread into the oocyte together with the nutrition transport from the follicular cells of the ovarioles and germarium to the developing oocytes. Based on the fact that the germarium would develop to oocytes and follicular cells, we deduced that RSV might initially infect germarium, which finally formed viruliferous oocytes, although RSV might also spread into oocytes when accompanied by the nutrition transport. Taken together, our results provide a possible mechanism that RSV can exploit the pathway for the nutrition transport into the oocytes, and finally transport into the blastodermal cells of the eggs.
