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Abstract
SUMMARY: 2,2-Dichloro-3,3-dimethyl-cyclopropane carboxylic acid (WL 28325) is a systemic fungicide highly specific for the rice leaf ‘blast’ disease caused by Piricularia oryzae Cav. Antifungal activity in vitro of WL 28325 against P. oryzae was dependent on the composition of the growth medium, growth being unaffected in two complex non-defined media but inhibited in a medium of defined composition. The antifungal effects of WL 28325 are probably not related to its activity as a rice ‘blast’ fungicide. Its intrinsic fungitoxicity was low. The ability of various di-chlorocyclopropanes of similar structure to WL 28325 to inhibit growth of P. oryzae in vitro did not correlate with their ability to prevent ‘blast’ on rice. Also, despite the high degree of pathogen specificity of WL 28325 as a disease protectant, WL 28325 inhibited the growth of several plant pathogens in culture.
No evidence was obtained to suggest that WL 28325 is converted, after its application to the rice plant, to a derivative of higher intrinsic fungitoxicity. These compounds may act by stimulating the disease-resistance mechanisms of the rice plant.
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