In vitro susceptibility test of Cladosporium cladosporioides isolates from Argentinian tomato crops against commercial fungicides

Abstract

Tomato cultivation is an important agricultural activity in northeast of Argentina, and disease control is indispensable for its production. The purpose of the current study was to identify two fungi isolated from tomato plants cultivated in greenhouses, with symptoms of leaf mould disease and a strain of the genus Cladosporium from a culture collection, and evaluate their in vitro susceptibility to four commercial fungicides. Macro and microscopic examination, molecular characterisation and sequence analysis were applied for identification. Broth dilution and spread plate methods were used to determine the minimal inhibitory concentration (MIC) and minimal fungicide concentration (MFC). The active ingredients of the products were azoxystrobin+difenoconazole, trifloxystrobin+tebuconazole, chlorothalonil and metalaxyl-M+mancozeb. The results were processed using the Kruskal-Wallis method. The isolates were identified as Cladosporium cladosporioidesa-c; consequently, lesions found on tomato plants did not correspond to Cladosporium fulvum. There was a significant statistical difference between the obtained values. Qualitatively, the three strains had a similar behaviour for chlorothalonil (MIC values: 0.25 - 0.5 μg/ml, MFC values: 4 μg/ml). In all cases, tests with metalaxyl-M+mancozeb yielded higher values than those achieved for chlorothalonil (MIC values: 8 μg/ml, MFC values: 8- 32 μg/ml). trobilurin-formulated fungicides were less effective against C. cladosporioidesa-b (MIC values: 16-256 μg/ml, MFC values: >64 μg/ml). C. cladosporioidesc was the most sensitive isolate. The information about the presence of a non-frequent fungus and its fungicide susceptibility, would be useful for establishing control strategies and enhance production.