In vitro evaluation of fungicides against clove isolate of Cylindrocladium quinqueseptatum in Sri Lanka

Abstract

Cylindrocladium quinqueseptatum is identified as a serious pathogen of Eugenia caryophyllata and a potential pathogen of Hevea brasiliensis in Sri Lanka. A total of 16 fungicides were screened against C. quinqueseptatum employing three screening techniques; conidial germination test (CGT), poisoned food technique (PFT), and soil fungicide screening test (SFST) to evaluate respectively, the efficacy of inhibiting conidial germination and mycelial growth and rendering microsclerotia non‐viable. Eight fungicides (benomyl, captan, chlorothalonil, mancozeb, metalaxyl 8% + mancozeb 64%, propineb, propineb 56% + oxadixyl 10% and thiram) were found to be effective in inhibiting conidial germination 100% (EC 100) at a very low concentration of 25 μg/ml. Three more fungicides, viz. oxadixyl 10% + mancozeb 56%, tebuconazole, and copper oxychloride achieved EC 100 in the same test at 100μg/ml, 200 μg/ml and 800 μg/ml respectively. However, only six fungicides, namely benomyl (EC 100 = 50 μg/ml), copperoxychloride (EC 100 =800 μg/m) metalaxyl + mancozeb 64% (EC 100 = 800 μg/ml), mancozeb (EC 100 = 1600 μg/ml) and propineb (EC 100 = 3200 μg/ml), reached the EC 100 in PFT. This number was further reduced in SFST and only five fungicides showed promising results. They were benomyl (EC 100 = 3200 μg/ml), mancozeb (EC 100 = 3200 μg/ml), metalaxyl+ mancozeb(EC 100 = 3200 μg/ml), chlorothalonil(EC100 =6400 μg/ml) and oxadixyl 10% + mancozeb 56% (EC 100 = 6400 μg/ml). However, only four, viz. benomyl, mancozeb, metalaxyl 8% + mancozeb 64% and oxadixyl 10% + mancozeb 56%, can be Identified as potential fungicides in the management of Cylindrocladium quinqueseptatum as these are the only fungicides which attained EC 100 in all screening tests.

The incubation period after treatment was of vital importance in CGT as low incubation periods provide misleading information on the efficacy of fungicides. It was also shown that one should be cautious in selecting the concentrations of test fungicides in SFST as all the fungicides tested required a very high concentration to obtain EC 100 in SFST.

Keywords:

• Cylindrocladium quinqueseptatum
• Eugenia caryophyllata
• Hevea brasiliensis
• fungicide screening