Abstract:
A series of single and binary action of allelochemicals were assessed under controlled
laboratory conditions by applying the Additive Dose Model on two weed species,
Eleusine indica (L.) Gaertn and Lemna minor L. to investigate the potential
allelopathic effect of five phenolic compounds (gallic acid, vanillic acid, caffeic acid,
coumarin and p-vanillin) and the joint action of phytotoxin mixtures on germination
and seedling growth of E. indica and degree of leaf discoloration of L. minor. Dose response
curves and ED50 values for single or binary mixture of phenolics, along with
possible observed inhibitory action were determined. In dose - response experiments,
coumarin and p - vanillin was demonstrated as the most phytotoxic inhibitors on
germination and seedling growth of E. indica while caffeic acid and vanillic acid
exhibited its strong effect on leaf discoloration of L. minor. The action of binary
combination of selected phenolic compounds was found to be more synergistic instead
of being additive and antagonistic. The mixture ratios which showed synergistic were
30% coumarin + 70% p-vanillin, 50% coumarin + 50% p-vanillin, 60% coumarin +
40% p-vanillin, 70% coumarin + 30% p-vanillin and 100% coumarin + 0% p-vanillin
for germination of E. indica; 0% coumarin + 100% p-vanillin, 30%coumarin + 70%p
vanillin, 40%coumarin + 60%p-vanillin, 50%coumarin + 50%p-vanillin,
60%coumarin + 40%p-vanillin, 70%coumarin + 30%p-vanillin and 100% coumarin +
0% p-vanillin for root growth of E. indica; 30% coumarin + 70% p-vanillin, 60%
coumarin + 40% p-vanillin and 100% coumarin + 0% p-vanillin only for fresh weight
of germinated E. indica and 0% vanillic acid + 100% caffeic acid, 30% vanillic acid +
70% caffeic acid, 40% vanillic acid + 60% caffeic acid, 50% vanillic acid + 50%
caffeic acid, 60% vanillic acid + 40% caffeic acid and 70% vanillic acid + 30% caffeic
acid for leaf discoloration of L. minor. The synergistic action observed could reflect
that the mixture compounds may contain different sites of action which interact to
form more toxic compound. This study has revealed the potential of phenolic mixture
for weed control.
