STUDIES ON THE PROPERTIES OF SOIL‐BORNE VIRUSES OF THE TOBACCO‐RATTLE TYPE OCCURRING IN SCOTLAND

Soil‐borne viruses of the tobacco‐rattle type occur in sandy and peaty soils in many parts of Scotland, and infect many species of crop and weed plants, often only in the roots. They also occur in potato plants that have diseases of the stem‐mottle type. The viruses can be distinguished from other soil‐borne viruses occurring in Britain by the symptoms they cause in tobacco, Chenopodium amaranticolor and French bean.

Some virus cultures (M types) multiplied readily and were easily transmitted by mechanical inoculation, whereas others (NM types) were transmitted mechanically only with difficulty. The behaviour of NM types remained constant during twenty successive subcultures. Only slight differences were noted between the symptoms caused by M and by NM types. A proportion of the single‐lesion isolates made from cultures of the M type behaved in every way like NM types: this proportion differed with different parent cultures. Single‐lesion isolates that were of the M type mostly caused somewhat different symptoms from their parent culture. All M types that were tested, including one from the Netherlands, were serologically related: however, different cultures, and different samples of the same culture propagated on different occasions, varied in antigenic constitution. Belladonna mosaic virus, described by Smith (1943) from England, was serologically related to tobacco rattle virus. Infection with each of several M types (including the Dutch culture), protected Nicotiana sylvestris plants from the effects of each of the others. NM types also protected N. sylvestris from the effects of the Dutch culture, but the latter was subsequently isolated from the tip leaves of such plants. Sap from plants infected with cultures of the M type contained characteristic rod‐shaped particles, but none was seen in sap from plants infected with NM types.

In tobacco sap, M types had the following properties: thermal inactivation point, 80–85°C.; dilution end‐point, 10^‐5‐10^‐6; longevity in vitro, over 6 weeks; infectivity survived freezing and precipitation by ammonium sulphate, but not exposure to pH 3. In many of its properties, including the unusual one of failing to show photoreactivation after ultra‐violet irradiation, tobacco rattle virus resembles tobacco mosaic virus.

Soil‐borne viruses occurring in Britain are classified into three groups, exemplified by tobacco necrosis, tomato black ring and tobacco rattle viruses.