Abstract
The effect of twenty-one phenolic compounds and related substances on conidial germination and appressorial formation inColletotrichum falcatum was studied.
Mono-phenol was only mildly inhibitory to spore germination at higher levels. Toxicity of di- and tri-hydroxy benzenes depended on the spatial relationship of the hydroxyl groups. The order of toxicity among the three dihydroxy isomers wasortho>para>meta. Germination inhibition followed the same pattern in the two trihydroxy isomers tested; pyrogallol was strongly toxic while phloroglucinal was without any significant effect. Methoxylation tended to abolish toxicity to spore germination as evidenced by anisole and guaiacol.
Acylation, either nuclear or side-chain, was strongly inhibitory to germination. Introduction of a carboxyl into phenol, on the other hand, dramatically brought down toxicity. Presence of a single hydroxyl group para to a carboxyl interestingly elicited strong inhibition of appressorial formation and increase in germ tube length. The limited number of phenolic compounds tested did not reveal any relationship between molecular weight and toxicity.
The presence on the nodal rind of certain phenolic substances may affect penetration of the pathogen into the host by suppressing appressorial formation,e.g., vanillic acid, ferulic acid, P-salicylic acid, P-coumaric acid and tyrosine. On the other hand their activity inside an infected tissue may facilitate rapid spread of the pathogen in the tissues and thereby lower the resistance of the host. It is suggested that different phenolic substances may be involved in the formation of dormant infections and have a bearing on epidemiology. Pathogenic strains are known to differ in the time of formation of hydrolytic enzymes. Since hydrolytic enzyme actionin vivo often releases phenols, it is suggested that the restricted virulence of certain strains is related to the earliness of formation of these enzymes.
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Communicated by Prof. T. S. Sadasivan,f.a.sc.
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Srinivasan, K.V., Narasimhan, R. The effect of certain phenolic and related compounds on spore germination and appressorial formation inColletotrichum falcatum went. Proc. Indian Acad. Sci. 74, 81–91 (1971). https://doi.org/10.1007/BF03050384
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DOI: https://doi.org/10.1007/BF03050384