Influence of Aliphatic Organic Acids and Metal Ions on Numbers of Local Lesions Produced by a Tobacco Necrosis Virus

SUMMARY: Many aliphatic organic acids, when sprayed on the leaves of bean plants, decreased the numbers of local lesions produced following inoculation with a tobacco necrosis virus. Citric and succinic acids were effective only when applied before or during the period of virus establishment. The inhibitory effect of these acids could be annulled by certain metal nitrates. The susceptibility of a species of host plant to a virus may vary greatly, as judged by the numbers of local lesions produced following inoculation with a standard preparation of virus.,4ge, nutrition, temperature, illumination and water supply are all known to affect susceptibility. Some of these factors alter the mechanical condition of the leaf, thus affecting the ease with which wounds necessary for virus entry are produced. Others are considered to alter ' host plant metabolism ' but the chemical basis for such changes is unknown. In an attempt to eliminate the daily cycle of variation in susceptibility to tobacco necrosis virus (Matthews, 1953) bean plants were grown under con-tinuous illumination for several days before inoculation. Such plants wer