Effect of Dinitroaniline Herbicides on Plant Resistance to Soilborne Pathogens

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Abstract
Seeds were sown in noninfested soil with or without herbicide at 1 .mu.g/g soil. After emergence, seedlings were either transplanted to Rhizoctonia solani-infested soil or inoculated with Fusarium [F. oxysporum f. sp. lycopersici, F. oxysporum f. sp. melongenae] or Verticillium dahliae. Generally, resistance to the diseases in herbicide-treated plants was increased. Trifluralin, nitralin, butralin and dinitramine significantly increased resistance of eggplant, tomato and pepper to R. solani; disease incidence was decreased by 30-90%. This increased resistance was dependent on inoculum and herbicide concentrations. Benefin and isopropalin did not affect plant resistance. Resistance of beans was not affected by trifluralin, nitralin or butralin, but was significantly decreased by dinitramine in 1 case. Trifluralin increased resistance of cotton to R. solani in certain cases and decreased it in others. The herbicides did not affect resistance of corn and oats to R. solani. Resistance of eggplant and tomato to Fusarium and Verticillium diseases was greatly increased by trifluralin and nitralin, resulting in as much as a 97% reduction in disease. Increased resistance occurred in spite of phytotoxic effects of herbicides. Trifluralin was detected in the hypocotyls of treated eggplants and cotton at concentrations of 0.84 and 0.15 .mu.g/g, respectively. Growth of the pathogens in vitro was inhibited at concentrations much higher than those used in soil or found in tissues.

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