Isolation of Tobacco Necrosis Virus from Buckwheat Plants

From leaves of naturally infected buckwheat plants (Fagopyrum esculentum Moench), cultivar Bcdnaja, an isolate of tobacco necrosis virus (TNV) was obtained. The virus was isolated mechanically, i. e. by means of sap inoculation, from infected buckwheat to healthy bean plants. The infected buckwheat plants were collected in north Bosnia and showed necrotic symptoms. This isolate differed from other TNV strains found in Yugoslavia earlier. The virus was identified as stipple streak strain of TNV following host plants reactions, stability in sap, serology, and electron microscopy. It provokes local necrotic reaction on many host plants, but systemic symptoms on beans (Fig. 1 B, C) and buckwheat cultivars (Fig. 1 A). The systemic reaction of bean consisted of necroses along the leaf veins, stems and fruits (Fig. 1 C). The buckwheat plants reacted with necroses on inoculated and young leaves, sometimes on the stem too, and with mosaic on top leaves. The thermal inactivation point was between 86 and 88 °C and longevity in vitro took more than 60 days at room temperature. In purified TNV preparations isometric particles with a diameter of about 26 nm were found (Fig. 1 D). In double diffusion serological reaction in agar-gel the TNV isolate from buckwheat reacted positively with an antiserum of TNV serotype A but not with an antiserum of serotype D