DYNAMICS OF FUNGICIDE RESISTANCE IN PENICILLIUM-DIGITATUM IN MINI-EPIDEMICS

By means of mini-epidemics, the changes in the proportion of conidia of Penicillium digitatum resistant to TBZ were simulated during two citrus packinghouse seasons in Greece under various fungicide regimes, vz. control (no fungicide), TBZ alone, TBZ and tridemorph in alternation and mixture. The disease incidence was consistingly lowest with the mixture, but the other treatments also lead to less disease incidence than the control. Within lesions of green mold, resistance to TBZ increased to 100 % from the 10 % in the start inoculum after the first: generation of fruits under TBZ treatment. With alternation and mixture, this level was reached after the second generation the earliest, whilst in the control chambers the proportion of resistant conidia remained practically unchanged around 10 %. A similar situation prevailed for the control in the aerospora of the chambers. Under TBZ, 80 to 97 % of the conidia in the airspace were resistant after the first generation and under alternation similar values were reached after two generation and under alternation similar values were reached after two generations when TBZ was applied in the sequence. The mixture had lower proportions of resistant conidia but occasionally values of 80 % and above were found.