Treatments with acetic acid followed by curing reduce postharvest decay on Citrus fruit

Citrus fruit are susceptible to many postharvest diseases and disorders, but Penicillium digitatum and Penicillium italicum are the most common and serious pathogens during storage and marketing. The continuous employ in packing houses of synthetic fungicides such as imazalil (IMZ) or thiabendazote for the control of these pathogens is promoting the selection of resistant biotypes. These considerations together with an increased attention for human health and the environment have multiplied the studies on new ecological technologies. In recent years researchers studies focused on alternatives to the chemical control of post-harvest decay, such as the utilization of GRAS compounds as well as physical methods. In the present study is reported the sequential use of acetic acid (AAC) followed by curing. The lemon variety "Verna" and the orange variety "Jaffa", naturally inoculated, were treated with vapours of AAC performed at three different concentration (15, 25 and 50 microL/L) for 15 minutes, after an incubation period of 24 hours at 27 degrees C and 90% relative humidity (RH). After treatments fruits were cured at 36 degrees C for 36 hours with 90% RH and subsequently stored at 8 degrees C and 90% of RH for eight weeks. Both citrus varieties were also treated with IMZ at a concentration of 200 mL/HL. At the end of the experiment decay and weight loss were evaluated. After 8 weeks of storage, in the lemon variety, the lowest percentage of infected wounds was 1.5% for both the fruit treated with IMZ or with AAC at 25 microL/L. Fruit treated with 15 mciroL/L or untreated (control) showed similar results with 13.6% and 16.6% of rotted fruit respectively. Different results were obtained with the orange variety, in this case the synthetic fungicide was the most effective at the end of the storage period, with 18.0% of decay. AAC treatments were not a successful as on lemons, the best result was achieved even in this case with AAC performed at 25 pL/L, but with 39.9% of decay. In both species the weight loss was not affected by the treatments. These results show that a good control of postharvest decay could be achieved, on lemon fruit, by combining the effect of a GRAS compound such as AAC with curing. Conversely the results obtained, by applying this control method to the orange variety were not so promising. Further researches are needed to shed light on the different behaviour between the two species.