ABSTRACT
M. W. Beijerinck was probably the first to provide evidence when he showed that healthy tobacco plants became infected with tobacco mosaic Tobamovirus (TMV) when they were grown in soil taken from around the roots of TMV-infected plants. Virus particles are known to be adsorbed to clay particles and organic plant debris and this considerably increases their longevity in soils and their stability to extremes of environmental conditions. Natural outbreaks of nematode-borne viruses are usually characterized by the occurrence in the crop of patches of infection that increase in size only slowly and which persist in these discrete areas for long periods, even after fallowing. Viruses and virus-like agents transmitted by soil-inhabiting fungi cause serious and economically important diseases of cereals, high-value horticultural crops, and root and tuber crops worldwide. Soil samples are usually mixed with sterile sand and placed in sterile pots using the precautions mentioned earlier to minimize abiotic transmission.
