| Maize dwarf mosaic (MDM) disease is the most important widespread viral disease of maize in the world. It has caused serious epidemics in the Northern regions of China since 1990. It can cause up to 100% yield losses due to the use of susceptible varieties and seed transmission of virus.Maize dwarf mosaic disease isolate collected from Beijing was purified and its nucleotide sequence of CP gene was analyzed. According to its characteristic and the homologous between the MDM isolate and the other MDM isolates in sequence of CP gene, the isolate used in our study was identified as sugarcane mosaic virus (SCMV). Subsequently the SCMV-specific polyclonal antiserum and the probe of CP gene were prepared to facilitate the study.This thesis was mainly focused on the seed-borne and seed transmission of SCMV in com (Mo 17 and 7922 corn varieties) by means of indirect-ELISA, infectivity, tissue culture, observation through the electron microscope, cross pollination, RT-PCR, Nucleic acid spot hybridization (NASH), Immunohistochemistry, and In Situ Hybridization Histochemistry (ISHH), the results showed as following:(1) The results of cross pollination experiment showed that the infected time was main effect factor to seed transmission, the highest percentage of infected seed was at 7 and 8 leaf stages (13.88% and 11.07% respectively), higher percentage was at 14 and 13 leaf stages (9.28% and 6.69% respectively), the least percentage was at 9 leaf stage (only 0.63%).(2) Bigger seeds transmitted SCMV was much higher percentage than small seeds in same ears. And the most of infected seeds distributed at the middle part of the ear.(3) The results showed that SCMV particles or inclusions were found in testa, aleuronic layer of endosperm and embryo tissue, not in starch layer of endosperm. Virus particle of aleuronic layer and embryo could entered maize seedling, might be relate to seed transmission. SCMV was found not only in immature embryo, butalso in the mature embryo. Embryo transmission of SCMV in immature and mature stages was proved.(4) The results of cross-pollination experiment showed that SCMV entered to seeds not only by pollen of infected plant through fertilization, but also by flower of infected maternal plant. The difference of transmission efficiencies between male and female plants showed that the later was the major pathway for SCMV entering to seed and embryo.(5) SCMV could be transported from mother plants to seeds. Virus entered the seeds and embryo during the early stage of seed development. It entered seeds of Mo 17 before 5 days of post pollination, between 5-10days of 7922 varieties, and entered embryo before 13-15days of post pollination in Mol7 variety.(6) The localization of SCMV in ovary was studied by Immunohistochemistry and In Situ Hybridization Histochemistry. The results showed that the virus distributd in the vascular bundle near to ovular pore, and speeded to the opposition side of the direction of pollen tube growth. But not found in the ovary or megaspore.(7) The results of localization of SCMV in infected seed showed that SCMV distributed in testa and embryo tissue.
|
PDF Full Text Request