The preservation of nine plant virus strains of tobamovirus and cucumovirus groups after freeze-drying in different lyophilic forms was examined. Quantitative studies on survival were performed. In tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV), accelerated storage test at 70 -100°C was applied for screening 20 protecting media. A perspective medium, 5% sorbitol, 3.6% dextran, for plant viruses lyophiliiation with high cryo-and xeroprotective effects was found.

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The antiphytoviral activity of 1-morpholinomethyl-tetrahydro-2(1H)-pyrimidinone (DD13) in a test system including protoplast cultures, surviving tissues and greenhouse plants was examined. The inhibitory effect was quantitatively investigated by immunofluorescence and enzyme linked immunosorbent assay. The antiviral action in vitro was 96%. The first 6 h after inoculation was the most sensitive period of the tomato mosaic virus (ToMV) reproduction cycle. DD13 possessed a protective effect in 97-100% plants infected with ToMV and cucumber mosaic virus (CMV).

Cucumber mosaic virus (CMV) is of great importance to the Bulgarian economy and hence a detailed knowledge of its diversity under local geographic and climatic conditions is required. An extended study was carried out on CMV strains the currently occur in Bulgaria. Fifty‐one isolates and strains found in different regions and various crops were biologically characterized and serologically differentiated into subgroups I and II using different variants of enzyme‐linked immunosorbent assay (ELISA) [double antibody sandwich (DAS)‐, antigen‐coated plate (ACP)‐, triple antibody sandwich (TAS)‐ with poly and monoclonal antibodies] and immunodiffusion tests. The ELISA modifications with monoclonal antibodies individually (ACP) or in combination with polyclonal antibodies (TAS‐ELISA) are suitable for mass screening of CMV isolates. The hyperimmune sera against strains from CMV subgroups I and II were very efficient for use in isolate differentiation via gel double immunodiffusion. The results obtained correlated with the polymerase chain reaction and restriction fragment length polymorphism data reported by other authors. The majority of the isolates belonged to subgroup I, whereas 10, mainly from tomato and pepper, belonged to subgroup II. Most of the subgroup II isolates came from the north of Bulgaria. The results of the present study will help to clarify the virus epidemiology and to develop specific control measures.

Studies on determination of appropriate conditions for cryogenic treatment and lyophilization of tobacco mosaic virus (TMV) in infected leaf tissue, plant sap and puritied preparation were carried out. The found parameters were: freezing to minus 22'C (for 1.5 hours); twelve-hours-sublimation at 50 Pa vacuum until 20°C temperature of the sample and secondary drying at l-2 Pa for 5-6, hours. Fifteen variants of cryoprotection were applied. TMV showed a survival higher than 89% after freeze-drying in glucose, fructose, maltose, lactose, sorbitol and the combinations with dextran. A technological scheme for automatic processing and standard work was developed.