Activity of Actigard® on Development of Phytophthora Root and Crown Rot on Pepper Plants
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AbstractPhytophthora blight of peppers (Capsicum annuum), caused by the oomycete pathogen Phytophthora capsici, occurs in most regions where this crop is grown. The root and crown rot phase of the disease develops on plants in areas of the field where soil remains saturated with water after an irrigation or rainfall. Subsequent periods of soil saturation encourage further disease development. Actigard (acibenzolar-S-methyl), is a chemical activator of plant disease resistance, has no known direct antifungal effects and is thought to mimic salicylic acid in the signal transduction pathway that leads to systemic acquired resistance (SAR). Foliar applications of Actigard were evaluated for suppression of root and crown rot on pepper plants growing in the greenhouse in pots and inoculated with Phytophthora capsici or grown in soil naturally infested with the pathogen. Inhibition of stem cankers on pepper cultivars Bell Tower and AZ9 after two to four treatments with Actigard was significantly greater than on plants receiving a single treatment of the chemical. Inhibition of stem canker elongation on Bell Tower or AZ9 peppers ranged from 93.2 to 97.2% and 87.4 to 92.4% when plants were inoculated with P. capsici at 1 or 5 weeks, respectively, after the fourth application of Actigard. Survival of chile pepper plants in field soil naturally infested with P. capsici was significantly increased by three foliar applications of Actigard compared to nontreated plants in all three trials when pots were watered daily and in two of three trials when pots were flooded for 48 hr every 2 weeks. When soil was flooded every 2 weeks, establishing conditions highly favorable for disease development, plants treated once with Ridomil Gold survived significantly longer than those treated with Actigard. On the other hand, when water was provided daily without periodic flooding, establishing conditions less favorable for disease development, there was no significant difference in plant survival between the two chemicals in two of three trials. Growth of shoots on chile pepper plants treated with Actigard, watered daily and grown in soil containing P. capsici generally was greater than nontreated plants. Pepper plants subjected to periodic saturated soil conditions and receiving three foliar applications of Actigard plus a soil treatment of Ridomil Gold survived significantly longer and produced a greater amount of shoot growth than plants treated with either chemical alone. This work suggests that Actigard could be an important management tool for Phytophthora root and crown rot on pepper plants.