In vitro antibiotic susceptibility of Erwinia sp. causing papaya (Carica papaya) black rot in Okinawa, Japan and several pesti-cides effectiveness on potted papaya plantlets before infection

Introduction - Papaya bacterial disease has spread all over the world and papaya black rot has been an epidemic in Okinawa Prefecture, Japan. The pathogen is Erwinia sp., identified by phylogenetic trees of 16s rRNA gene and four housekeeping genes. There is only one pesticide, Orthocide, registered in Japan, but it is not enough to counter the disease spread. Objective and method - To hunt for other pesticide candidates, antibiotics were examined using minimum inhibitory concentration assay and resulted in oxytetracycline and streptomycin strongly inhibiting the papaya black rot pathogen. Besides, the test using potted papaya plantlets was performed in the condition the pesticides were applied before potted papaya plantlets were infected, using several pesticide candidates. Results and discussion - Captan (Orthocide), mancozeb, copper (II) hydroxide, and oxytetracycline exhibited a preventive effect on black rot on potted papaya plantlets. Especially, captan was found to be stronger when it was sprayed before the infection of potted papaya plantlets with black rot. However, streptomycin did not. Conclusion - Mancozeb, copper (II) hydroxide, and oxytetracycline should also be approved to register as papaya black rot. Specifically, using the time of copper (II) hydroxide against papaya soft rot is unlimited, and it would be useful and effective for papaya black rot by being registered for legal expansion.