Assaying Levels of Virus with Local Lesion Hosts

A number of methods have been used for the quantitation of virus within infected plants. Early ones used physical techniques such as dry-wt and particle counts; more recently, serological and nucleic acid-based methods have been developed. These methods are all based on a physical aspect of the virus particle, and all measure total amounts of virus (or viral component), regardless of infectivity. Holmes (1 ), however, was the first to utilize the observation that mechanical inoculation of tobacco mosaic virus (TMV) onto the leaves of Nicotiana glutinosa led to the formation of local lesions, and that the number of local lesions was inversely correlated to the dilution of the inoculum. The local lesion assay remains the simplest method to quantitatively measure the most important biological property of a sample of virus, that of the presence of viable virus particles.