Abstract
Point mutation G143A in the cytochrome b (Cyt b) protein commonly confers resistance to quinone outside inhibitor (QoI) fungicides in phytopathogenic fungi, including Corynespora cassiicola, which causes cucumber target spot disease. However, the effect of G143A on the binding between the QoI fungicide and the Cyt b protein, and the use of LAMP (loop-mediated isothermal amplification) to detect this point mutation had not been reported previously in C. cassiicola. In this study, the sensitivity of 131 C. cassiicola isolates—collected from Shandong province, China in 2019 and 2020—to pyraclostrobin was determined. The EC50 values ranged from 1.67 to 8.82 μg/mL, and sequencing results showed that all C. cassiicola isolates contained the G143A mutation. Molecular docking results suggested that G143A significantly alters the affinity of pyraclostrobin to the Cyt b protein. Following development of three LAMP primer pairs, the best reaction condition for LAMP analysis was 65 °C for 60 min, and the detection limit was 0.01 ng/μL of DNA containing the point mutation. In conclusion, the G143A mutation conferring pyraclostrobin resistance is widespread in C. cassiicola from Shandong province, and the LAMP method can be used to monitor QoI resistance in C. cassiicola caused by the G143A mutation in the field.
Highlights
Cucumber target spot is a worldwide fungal disease in cucumber production [1,2].It is caused by Corynespora cassiicola, which can infect a wide range of hosts, including nematode cysts and the human skin [3,4,5,6]
Continuous resistance monitoring is of high significance for rational application of quinone outside inhibitors (QoI) in the protection and control of cucumber target spot disease
The EC50 values of pyraclostrobin for field isolates collected in this study were 1.67–8.82 μg/mL, similar to the data (0.51–7.01) for eight G143A-containing C. cassiicola strains for pyraclostrobin reported by Duan et al [12]
Summary
Cucumber target spot is a worldwide fungal disease in cucumber production [1,2]. It is caused by Corynespora cassiicola, which can infect a wide range of hosts, including nematode cysts and the human skin [3,4,5,6]. Chemical control is the main method to limit cucumber target spot disease in China. The domestically registered agrichemicals for the prevention and control of this disease include quinone outside inhibitors (QoI) (pyraclostrobin, trifloxystrobin, azoxystrobin), succinate dehydrogenase inhibitors (SDHI) (pydiflumetofen, fluopyram, fluxapyroxad), and sterol biosynthesis inhibitors (SBI) (difenoconazole, tebuconazole, prochloraz)
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