Avaluació de sistemes alternatius als fungicides sintètics per al control de les podridures verda i blava en postcolllita de cítrics

Economic losses caused by postharvest diseases are among the major concerns of the citrus industry worldwide. In our Mediterranean conditions, wound pathogens are the principal cause of postharvest decay. Postharvest green mold, caused by Penicillium digitatum (Pers.: Fr.) Sacc., and postharvest blue mold, caused by P. italicum Wehmer, are the most economically important citrus postharvest diseases. Typically, these diseases are primarily controlled by application of synthetic fungicides. Alternative methods are needed because the widespread use of these chemicals in commercial packinghouses has led to the proliferation of resistant strains of the pathogens and iatrogenic diseases. Furthermore, concerns about human health risks and the protection of the environment associated with fungicide residues have increased the need to find and develop alternatives to fungicide usage. This is the basic objective of the present doctoral thesis. Firstly, fruit epiphyte and environmental fungal populations in 'Clemenules' orchards in Tarragona (Chapter 1) and fungal populations and fungicide-resistant biotypes of Penicillium spp. in the atmosphere and on surfaces of equipment and facilities in Tarragona citrus packinghouses (Chapter 2) were characterized. Then, different physical, chemical, biological, and combined methods were evaluated for the control of citrus postharvest green and blue molds. Hot water, sodium carbonate, and sodium bicarbonate treatments were extensively studied (Chapters 3 and 4); numerous other food additives and low-toxicity compounds were evaluated (Chapter 5); and the effect of gaseous ozone exposure during cold storage was investigated (Chapter 6). Finally, antagonistic microorganisms effective for the biological control of green and blue molds were isolated, identified, characterized, and assayed in combination with other alternative methods (Chapters 7 and 8). The following are some of the most important conclusions: the pathogenic genus Penicillium is present through the entire harvesting period in 'Clemenules' orchards. Fruit from the orchards are the major source of fungal contamination in the packinghouses. Both thiabendazole- and imazalil-resistant biotypes of P. digitatum and P. italicum were found in Tarragona packinghouses. Brief dips in 2 or 3% sodium carbonate or sodium bicarbonate solutions are more effective than hot water alone for the control of green and blue molds on oranges and clementine mandarins. These treatments are synergic to heat (45ºC) and their activity is fungistatic and not very persistent. Other effective treatments are brief dips in hot solutions of potassium sorbate, sodium benzoate, ammonium molybdate, and sodium molybdate. Storage at low temperature (5ºC) under an ozonated atmosphere (0.3 or 1.0 ppm ozone) does not reduce green and blue mold incidence on oranges and lemons but does delay disease development and prevent sporulation of the pathogens. The strain CPA-2 of the bacterium Pantoea agglomerans is an effective antagonist for the biological control of postharvest green and blue molds on oranges and clementines. Its action is satisfactorily complemented by a previous 2% sodium bicarbonate treatment.