Fungicide resistance of Phytophthora palmivora causing durian diseases in eastern and southern Thailand and the in vitro alternative control by cajeput leaf extracts

Abstract

The results showed that 24 and 25 of 40 collected isolates of Phytophthora palmivora were resistant to metalaxyl and mancozeb, respectively with the 50% effective concentration (EC50) higher than 100 mg/L. Meanwhile, all isolates were resistant to fosetyl-al with EC50 higher than 1000 mg/L. Moreover, mapping between the survey areas and all Phytophthora isolates with the resistant levels to the 3 tested fungicides was depicted. Interestingly, 20 of 40 isolates showed multiple fungicide resistance to all tested fungicides with different modes of action, thereby selecting for the in vitro evaluation of the cajeput extract effect. Lower than expected, only 9 out of 20 multiple fungicide resistance isolates were shown to be significantly sensitive to the 10000, 20000 and 40000 ppm of cajeput extract based on paper disc assay.