Effective mechanical inoculation of plant viruses in the absence of water

Abstract

Tests with powdered, dry inocula prepared from virus-diseased leaves by grinding the latter in liquid nitrogen and freeze-drying the finely divided tissue, resulted in high infection rates of a variety of plant species. Ten widely differing viruses and 12 test species belonging to seven plant families were investigated. It was shown that early virus–host interactions leading to virus establishment in the test plants in the course of mechanical inoculation generally do not require the mediation of water. With some test species dry inoculation was even more effective than sap inoculation, irrespective of the presence or absence of (proteinaceous) virus inhibitors in the inoculum. In the presence of inhibitors the effectiveness of dry inoculation seems to depend on a spatial separation of viral and inhibitory agents, because inhibition of virus establishment per se was also found not to require water. The effectiveness of dry inoculation appears to depend further on host characteristics, probably of an ultrastructural nature, as well as on properties of the viruses. Isometric virions and those approaching isometry might be more effective in dry inoculation than elongated ones. Electron microscopic examination of the dry leaf powders revealed the virions to be present mostly as monomers of rather uniform length.