Competition Between Pyrimorph-Sensitive and Pyrimorph-Resistant Isolates of Phytophthora capsici

Abstract

Phytophthora capsici causes significant losses to vegetable production worldwide. Pyrimorph, a new carboxylic acid amide fungicide, has been registered to control P. capsici in China. A mutation (Q1077K) in cellulose synthase 3 has been reported to confer resistance to pyrimorph. In this study, we measured the competition between pyrimorph-resistant and pyrimorph-sensitive isolates of P. capsici. Mixed zoospore suspensions of resistant (R) and sensitive (S) isolates at five ratios (1R:9S, 3R:7S, 5R:5S, 7R:3S, and 9R:1S) were applied to carrot agar in vitro test (with five successive transfers) and to the soil surface around pepper plants in planta test (with 10 successive disease cycles). The proportion of resistant isolates was measured by a conventional assay in which single zoospore isolates recovered after transfers or disease cycles were grown on agar medium with a discriminatory concentration of pyrimorph. The results were then compared with those of a real-time polymerase chain reaction (PCR)-based method developed here, the results were similar. Both assays showed that the competitive ability of the resistant isolates was similar to or less than that of the sensitive isolates. The real-time PCR assay developed will be useful for high-throughput analysis and monitoring the development of pyrimorph resistance in field populations of P. capsici.

Soft selective sweeps in fungicide resistance evolution: recurrent mutations without fitness costs in grapevine downy mildew

“…Their results were variable, ranging from no fitness cost (Pang et al . ), variable fitness costs depending on pathogenicity trait or strain (Wang et al . ) to a lower pathogenicity of resistant isolates (Zhu et al .…”

Quantitative proteomics links metabolic pathways to specific developmental stages of the plant‐pathogenic oomycete Phytophthora capsici

“…Cultures of P. capsici isolate Hd11 were established as described previously (Pang et al ., ) and maintained on potato dextrose agar (PDA). The mycelium was collected from 3‐day‐old cultures (potato dextrose broth) of 100 mL grown at 25 ºC in the dark, whereas the asexual sporangia and zoospores were obtained by growing P. capsici on V8 agar plates under 12‐h light/12‐h dark cycles over a period of 7 days (Pang et al ., ). The zoospores were stimulated to encyst by vigorous shaking for 1–2 min.…”