Environmental fitness of metalaxyl-resistant isolate of Phytophthora capsici

Abstract:

Abstract:［Objective］ The environmental fitness of metalaxyl-resistant isolate of Phytophthora capsici was studied for assessing the risk of metalaxyl-resistant P．capsici．［Methods］We studied the main biological characteristics，competitive ability on plate，pathogenicity on pepper plant and adaptability in soil of the laboratory-induced metalaxyl-resistant isolate of P．capsici (Pc2-3 strain)，with the metalaxyl-sensitive isolate (Pc2 strain，the wild-type) as the control.［Results］The zoosporangia production，releasing rate of zoosporangia and germination rate of zoospores of Pc2-3 were less than that of Pc2．The temperature range，optimum temperature range and initial pH range for mycelia growth of Pc2-3 were consistent with that of Pc2，but mycelia growth rate of Pc2-3 was lower than that of Pc2． Pc2-3 exhibited significantly weak competitive ability compared with Pc2 on carrots plate．Disease incidence of pepper inoculated with Pc2-3 (14.3%) was significantly lower than that of Pc2 (88.6%)．When pepper plant was inoculated by mixtures of zoospore suspension of Pc2-3 and Pc2 at same ratio，the disease incidence，closing to that by Pc2 strain，was 75.7%．And all the strains isolated from diseased plants in the treatment were metalaxyl-sensitive．The density of P．capsis Pc2-3 was 0.28 times of Pc2 after the soil inoculated with Pc2-3 and Pc2 respectively at same zoospores density was incubated for 20 days．Otherwise，the ratio of Pc2-3 to Pc2 was 0. 42 if the metalaxyl concentration in the soil was 300 mg/kg dry soil．No matter the soil temperature and humidity were beneficial to survival of P．capsici or not，Pc2-3 showed lower soil adaptability than Pc2．［Conclusion］ The environmental fitness of metalaxyl-resistant P．capsis Pc2-3 was weaker than the metalaxylsensitive strain Pc2 (the wild-type)．