Chemical Nature of a Plant-Virus Inhibitor from Rice

Abstract

THE inhibition of tobacco mosaic virus infection of primary bean leaves (Phaseolus vulgaris L. var. Pinto) by extracts of various portions of rice plants has been described recently¹. The inhibitor or inhibitors present in rice resemble those derived from other plants such as spinach (Spinacea oleracea L.)², poke weed (Phytolacca acinosa Roxb. var. esculenta)³, New Zealand spinach (Tetragonia expansa Murr.)⁴, and sweet william (Dianihus barbatus L.)⁵, in that the infection of test plants is inhibited when the plant extract and virus inoculum are mixed and applied simultaneously. The inhibitor in rice extracts differs in that it protects bean leaves against tobacco mosaic virus infection even when applied to the leaves (which are then rinsed with water) 1–3 days prior to inoculum application. In so far as we are aware, the only other plant extracts that protected test plants against virus infection were derived from carnation (Dianthus caryophyllus L.)⁶, but the time between inhibitor application and inoculation was only 1–3 hr.