Leaf extracts of pepper, geranium, and jimsonweed inhibited the development of local lesions induced by tobacco mosaic virus (TMV) on Pinto bean leaves when mixed with the inoculum; sprayed on the underside of the leaf before inoculation of the upper surface; or sprayed on the upper leaf surface after inoculation. The extracts also inhibited lesion development on the primary leaf opposite to the one on which they were applied. The inhibitory activity of the geranium and pepper extracts was separated into two fractions; one with a molecular weight greater than 50ensp;000 and one with a molecular weight range of 1000ndash;50ensp;000. The inhibitory activity of the jimsonweed extract was present in the high molecular weight fraction only. The high molecular weight fraction from pepper was inhibitory when applied to the underside of the leaf. This evidence, and that supplied by the jimsonweed extract, indicates that high molecular weight fractions are capable of inducing a systemic resistance even when applied to uninjured tissue.
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