CULTURAL CHARACTERISTICS, RESPONSE TO FUNGICIDES AND AGGRESSIVENESS OF ISOLATES OF CERATOCYSTIS PARADOXA

摘要

THE FUNGUS Ceratocystis paradoxa is an important pathogen of sugarcane that causes pineapple sett rot, a decay of seed pieces. At times, complete control of the disease by dipping cuttings in a fungicide has failed. A number of factors could be responsible for this situation, one of them being fungicide resistance. A study was undertaken to examine variability of the pathogen and to find alternative fungicides and methods for disease control. Nineteen isolates of C. paradoxa were isolated from 73 soil samples obtained from various regions of Mauritius. The isolates differed in their colony morphology, growth rate and sensitivity to temperature. The inhibitory effect of the fungicides benomyl, thiophanate-methyl and difenoconazole+carbendazim were compared in vitro. The effective dose of benomyl that inhibited growth of colony size by 50% (ED_(50)) varied from 0.31 to 0.88 ppm. The ED_(50) for thiophanate-methyl was higher, 13-24 ppm, while that of difenoconazole+carbendazim was 0.21-0.23 ppm. The latter mixture was most effective and all isolates were equally sensitive to it, in contrast to the two other fungicides. When difenoconazole was used on its own, its ED_(50) was 0.28 ppm. A pathogenicity test with the 19 isolates was carried out on varieties M 1176/77, M 52/78 and R 570. One isolate did not cause any infection, some infected only one or two varieties, while others infected all three. Based on the progress of the infection, M 1176/77 was most resistant and R 570 was least. The variability of the fungus is of interest in understanding its epidemiology and the establishment of appropriate control measures.