Identification and Effects onXanthomonas campestrispv.malvacearumof Two Phytoalexins from Leaves and Cotyledons of Resistant Cotton

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Abstract
Two compounds that inhibit growth of X. campestris pv. malvacearum were isolated from leaves and cotyledons of inoculated bacterial blight-resistant lines of cotton (G. hirsutum). Chromatographic and spectral properties indicated that they are 2,7-dihydroxycadalene and its oxidation product, the yellow fluorescent compound lacinilene C. Extracts of inoculated blight-susceptible or uninoculated blight-resistant leaves contained much lower amounts of both compounds. 2,7-Dihydroxycadalene at 0.35 mM caused a 50% reduction inthe number of bacterial generations in a liquid culture bioassay. Preparations of lacinilene C from plants of resistant cotton lines WbM(0.0) and Im216 were optically active, but exhibited ellipticities of opposite signs; they caused 50% inhibition at .apprx. 0.4 mM and 1.5 mM, respectively. The amounts of 2,7-dihydroxycadalene and lacinilene C extracted from inoculated resistant leaves were approximately 1/10 of the amounts required to account for the observed inhibition of X. campestris pv. malvacearum, if those compounds were uniformly distributed throughout the tissue water.