Sensitivity of Phytophthora infestans to flumorph: in vitro determination of baseline sensitivity and the risk of resistance |
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Authors: | S K Yuan X L Liu N G Si J Dong B G Gu H Jiang |
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Institution: | Department of Plant Pathology, College of Agronomy and Biotechnology, China Agricultural University, Beijing 100094;;ShenYang Research Institute of Chemical Industry of China, Shenyang 110021, China;;Temasek Life Sciences Laboratory, National University of Singapore, 117604, Singapore;and;Center of Agrochemicals for Biological and Environmental Technology, Institute for the Control of Agrochemicals, Ministry of Agriculture, Beijing 100026, China |
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Abstract: | The sensitivity of 127 Phytophthora infestans isolates to flumorph was determined in 2003 and 2004. The isolates originated from two geographical regions and showed similar levels of sensitivity in both years. Baseline sensitivities were distributed as a unimodal curve with EC50 values for growth of mycelia ranging from 0·1016 to 0·3228 µ g mL?1, with a mean of 0·1813 (± 0·0405) µ g mL?1. There was no cross-resistance between flumorph and metalaxyl. Laboratory studies were conducted to evaluate the risk of P. infestans developing resistance to flumorph. Mutants resistant to metalaxyl or flumorph were obtained by treating mycelium of wild-type isolates with ultraviolet radiation. Metalaxyl-resistant mutants were obtained with a high frequency and exhibited resistance factor values (EC50 resistant/EC50 sensitive phenotypes) of more than 100, while flumorph-resistant mutants were obtained at much lower frequencies and had very small resistance factors (1·5–3·2). There was cross-resistance between flumorph and dimethomorph, but not with azoxystrobin or cymoxanil. Most flumorph-resistant mutants showed decreases in hyphal growth in vitro and in sporulation both in vitro and on detached leaf tissues. These studies suggested that the risk of resistance developing was much lower for flumorph than metalaxyl. However, as P. infestans is a high-risk pathogen, appropriate precautions against resistance development should be taken. |
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Keywords: | azoxystrobin cymoxanil dimethomorph fungicide resistance metalaxyl potato late blight |
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