DETECTION AND CONTROL OF Streptomyces scabies LAMBERT & LORIA IN POTATO (Solanum tuberosum L.) TUBERS IN THE MAYO VALLEY, SONORA, MEXICO

Abstract

In 2011 and 2012, severe symptoms of rot and scab were observed on cv. Fiana potato tubers in the Mayo Valley, Sonora, Mexico. The incidence of this disease in the region ranged from 30-40%, which resulted in severe losses in the quality of the potato tubers harvested during both production season. The objectives of this study were to identify the causal agent of these symptoms and evaluate possible potato seed treatments to control this disease under field conditions. Detection and identification of the plant pathogen was based on morphological, physiological, pathogenic and molecular analysis. Effectiveness of the following treatments were evaluated : fluazinam, copper hydroxide, mancozeb, chlorothalonil, oxytetracycline + streptomycin and antagonistic bacteria. All of them were applied to infected potato seeds in order to reduce the severity of the disease Each treatment was applied at planting time and a second application was made as a drench 45 days after planting. Effectiveness of the treatments was assessed at harvest using a severity scale. After a thorough analysis which combined morphological, physiological, molecular and pathogenicity tests, Streptomyces scabies was identified as the causal agent of scab symptoms and rot in potato tubers. The seed treatments with the lowest percentage of infection were fluazinam, oxytetracycline + streptomycin, chlorothalonil and mancozeb.