Angela Yordanova

Application of accelerated storage test to lyophilized plant viruses

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 lyophilization with high cryo- and xeroprotective effects was found.

Determination of parameters for tobacco mosaic virus cryogenic treatment and freeze-drying

Studies on determination of appropriate conditions for cryogenic treatment and lyophilization of tobacco mosaic virus (TMV) in infected leaf tissue, plant sap and purified 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 1–2 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.

A model for longevity prediction of freeze-dried tobamoviruses

An accelerated storage test was carried out on freeze-dried samples of five variants of tomato mosaic virus – from leaf material, plant sap and purified preparation with and without protectant, at 28, 37 and 45 °C. A model for longevity prediction of lyophilized tobamoviruses was developed. The preservation of tomato mosaic virus decreased to 10% after 0.7–2.8 years in unprotected variants and after 7.5–11 years in protected samples under real storage conditions. Experimental data have confirmed the predicted values.

PREDICTION OF THE PRESERVATION OF LYOPHILIZED TOBAMOVIRUSES

ABSTRACT Eleven tobamovirus strains were lyophilized in the form of leaves, plant sap with and without protectant, as well as protected purified preparation. Accelerated storage test at 28–81 °C for 30 to 240 days was applied to the freeze-dried samples. The infectivity was tested on a local host. The survival decrease was represented as pseudo-first order reaction and predictions for stability of lyophilizates at real storage conditions (4 °C) were developed by means of Arrhenius equation. The preservation depended on the lyophilic form and was strain specific. Some strains were expected to loose 90% of the survival after 1–3 years while others—after more than 25 years in unprotected variants. The preservation as protected purified preparations will be more than 60–70 years. Among the tested strains of tomato mosaic virus the highest longevity for the strains of group “2” after Pelham was predicted. The accelerated storage test and the prediction facilitate the maintenance of a plant virus collection.

Electrophoretic mobility of different in pathogenicity strains of Tobamovirus group

Twenty four Tobamovirus strains divided according to their ability to overcome the resistance genes in tobacco and tomato as well as in their severity of systemic symptoms were tested. Significant differences between means of particle mobility of the virus groups were found especially about yellow mosaic strains which were distinguishable enough by the electrophoretic analysis.