In vitro pesticides susceptibility of Erwinia sp. causing papaya (Carica papaya) black rot in Okinawa, Japan and captan effectiveness on papaya pot seedlings
2022
Hanagasaki, Takashi | Takushi, Tetsuya | Kawano, Shinji | Yamashiro, Maki
Since 2002, papaya black rot has been spreading over several islands of Okinawa Prefecture. The pathogen of the disease was identified as Erwinia sp., genetically close to E. mallotivora and E. papayae. In terms of the disease transmission, it is probably carried by the wind or rain. In order to devise a prevention strategy for the disease, in vitro pesticides susceptibility of the pathogen and tests with papaya pot seedlings were conducted. A minimum inhibitory concentration assay demonstrated that copper (II) hydroxide, basic copper sulfate, and captan present in the papaya-registered pesticides inhibited the growth of the pathogen on nutrient agar plates. In addition, mancozeb that is non-papaya-registered pesticide also showed an inhibitory effect on the pathogen. Thus, there is a high possibility that even the existing papaya-registered or non-papaya-registered pesticides can prevent papaya black rot. In the test with papaya pot seedlings, copper (II) hydroxide exerted a relatively lower pesticide effect; however, captan exhibited a pesticide effect, although it is one of the fungicides not registered for use in the treatment of bacterial diseases of plants in Japan till date. Indeed, based on the result of the present study, the official registration of legal expansion for use of captan to control papaya black rot was approved in Japan on December 22, 2021.
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