Changes in surface microflora of apple and pear fruits by application of pesticides and their relation with biocontrol of post-harvest diseases

摘要

The evolution of natural microflora of apple and pear fruits during ripening was studied in relation to the application of pesticides which the producer uses to combat preharvest pests with the aim of determining how the pesticide application might be manipulated to enhance the beneficial effect of the natural microfiora against post-harvest diseases. Before the pesticide application (deltamethrin plus dicofol or esfenvalerate plus dicofol), yeasts dominated the fruit epiphytic microflora, whereas after the treatments, moulds dominated. Twenty days after the last application, the dominating flora was still moulds, but 30 days after the treatment (final harvest), yeasts predominated again. In vitro assays of pesticide toxicity for yeasts showed that deltamethrin was more toxic than esfenvalerate and dicofol was the lowest toxic one. None of the three pesticides was toxic for the pathogen Penicillium expansum. The assays of fruit wound colonization showed that wounds were colonized by moulds or yeasts depending on the harvest time (20 days or 30 days after the pesticide application). Rhodotorula glutinis and Cryptococcus laurentii from epiphytic microfiora were effective for reduction of incidence of blue mould on apples. Thus, a yeast dominated microflora could be a natural agent of rot control. The appropriate timing of preharvesl pesticide applition in relatio to beneficial microflora of fruits, and the need to include the fruit microflora among the ecological selectivity tests of preharvest pesticides are discussed.