Treatment with UV-C light followed by NaHCO3 application has synergic activity against citrus green mold

Abstract

The enduring confrontation between fungal pathogens and hosts during storage and shelf-life, along with the restricted number of fungicides for postharvest use, have led to the selection of biotypes able to overcome the mode of action of several fungicides, in several citrus growing areas. In order to control R-biotypes and fulfill the restrictions, thorough researches have been undertaken on alternative approaches. Until now, single alternative treatments have not yet reached comparable results to synthetic fungicides. To overcome this difficulty, treatments have been combined with the aim to find synergic interactions. Here we report encouraging results obtained by applying NaHCO 3 (SBC) to lemon fruit treated with UV-C light (254 nm). Lemon fruit (Citrus limon 'Verna') were harvested twice (April and August) and at each harvest fruit was graded, rinsed and when dry divided into 4 groups (each of 180 fruit) according to the following treatments: I) none; II) UV-C (3 kJ m -2 ); III) NaHC0 3 2% (w/v); IV) UV-C followed by NaHCO 3 . The treatment with NaHCO 3 was carried out by immersing the fruit, for 15 s, in the solution heated at 60°C. In the combined treatment UV-C lightening was performed 5 min before immersion. Following treatment fruit was kept for 2 months at 5°C and 90±5% RH followed by a 6-day simulated marketing period (SMP). Natural decay was monitored after 1 month, at the end of storage and SMP. The same experiment was conducted with fruit artificially inoculated with Penicillium digitatum (10 5 conidia ml -1 ) and kept at 25°C and 90% RH for 5 days. In untreated fruit the degree of decay was greater in early compared to late harvested lemons. Nearly 65% of the early harvested un-treated fruit was lost by the end of the experiment, while only 42% of the late harvested ones rotted. Decay was significantly reduced only by combining the two treatments. Indeed, the decay percentage for early and late harvested lemons subjected to the combined treatment was 8.0 and 5.2%, respectively. The results obtained with artificially inoculated fruit confirmed the trend observed in the storage trials.