Effect of a postharvest treatment with natural fungicides on the epiphytic populations of Geotrichum candidum on nectarines

Sour rot of stone fruit caused by Geotrichum candidum is a frequent problem for Chilean growers, being especially problematic when arriving to international markets. The epiphytic population on the fruit is reduced by fungicides sprayed in the orchard, but most of the packed fruit harbors the pathogen due to recontamination in the packinghouse. The objective of the study was to evaluate the effect of the natural fungicides Serenade^® or Timorex Gold^®, on the epiphytic population of G. candidum, and to evaluate possible effects on fruit shelf life. Experiments were conducted in commercial packinghouses on ‘Summer Fire’, ‘Venus’ and ‘Honey Diva’ nectarines, and ‘Zee Lady’ peaches. The natural fungicides were used at 2, 3 and 4% mixed with fludioxonil in a rate of 2,500 mL 100 L^‑1 of wax. Boxes of fruits were taken at the end of the packing line; half of them were cold stored (0±1°C) for 40 days plus 10 days at room temperature simulating commercial conditions, the other half were frozen at -17°C for 4 days and let to unfreeze, when the number of fruits with saprophytic development of G. candidum were counted. The treatments effect was measured as the percent of fruits with pathogen development. Percent data was analyzed with ANOVA and mean values separated with Fisher LSD (p≤0.05). At least 91% of the fruit treated only with fludioxonil had development of G. candidum. Serenade reduced the epiphytic population from 62.1 to 77.3% while Timorex Gold had no effect at 2% but reduced the population to 75.0 or 80.7% when used at 3 and 4%, respectively. Fludioxonil treated ‘Venus’ nectarines stored for 40 + 10 days had 100% of total rot, while the rot was reduced to 48 and 25% when treated with fludioxonil mixed with Serenade or Timorex Gold, respectively.