Graduate Thesis Or Dissertation

Isolation and identification of dahlia viruses

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  • Three viruses were isolated from dahlias using a modification of Yarwood's leaf-disc method of inoculation. Two of these isolates have been reported previously in dahlias. In addition, a fourth virus was isolated using a liquid-nitrogen transmission technique. Dahlia virus isolate 1 possessed host range and thermal inactivation properties similar to those reported for dahlia mosaic virus. Attempts to partially purify and prepare an antiserum for dahlia virus 1 were not successful. Dahlia virus isolates 2 and 3 showed host range and thermal inactivation properties similar to those obtained in tests with tomato spotted wilt and CMV virus type cultures. Dahlia virus 2 was partially purified using a procedure developed by Grogan and Kimble for CMV purification. An antiserum prepared to the virus did not react when tested with the CMV type culture. However, a positive reaction was obtained in gel diffusion tests when an antiserum prepared by Grogan to CMV (Imperial Strain 78) was tested with the dahlia isolate. Dahlia virus 4 expressed symptoms on several hosts and possessed thermal inactivation properties similar to tomato ringspot virus. An antiserum prepared to this isolate reacted positively in a microprecipitin test with tomato ringspot virus. Gel diffusion tests showed that extracts from tomato ringspot and dahlia virus 4 possessed antigens common to both viruses. However, tomato ringspot virus possessed a major antigenic component which was not present in extracts from plants infected with dahlia virus 4. Attempts to eliminate viruses present in naturally infected dahlias using heat and chemical treatments were not successful. Symptoms on Unwin's hybrid seedlings infected with dahlia virus isolates 3 and 4 differed from symptoms on the dahlia varieties from which the isolations were made. Seedlings infected with dahlia virus isolates 1 and 2 showed systemic symptoms which were similar to those on the original varieties. Diagnosis of specific virus diseases in dahlia is difficult because of the variation in symptom expression resulting from infection with a single virus. Therefore, only a general diagnosis of a virus disease is possible based on the symptoms observed in naturally infected dahlias.
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