Abstract
Imazalil and Thiabendazole chemical based fungicides are currently used to control citrus green/blue molds, which is mainly caused by <i>P. digitatum</i> and <i>P. italicum</i>. In order to find alternative methods for control of citrus fruit diseases to avoid fungicide caused health and environmental problems, current research was conducted to explore the antifungal effectiveness of H<sub>2</sub>O<sub>2</sub>-Ag<sup>+</sup> (Hydrogen peroxide stabilized with silver ions), which is a universally applicable and high effective disinfectant against pathogenic microorganisms, and has been used to control postharvest decay of fresh fruits in most developed countries, in the context of <i>in vitro</i> and <i>in vivo P. digitatum</i> and <i>P. italicum</i> development in the Newhall navel orange. H<sub>2</sub>O<sub>2</sub>-Ag<sup>+</sup> was found to be effective in inhibiting in vitro radial growth and <i>in vivo</i> inoculated lesion development of <i>Penicillum italicum</i> and <i>Penicillum digitatum</i>. Dipping fruit with H<sub>2</sub>O<sub>2</sub> at concentrations of 1-2% before storage reduced the decay incidence of orange after 30 and 60 days cold storage following by 3 days shelf life, although it was less effective than the positive control of fungicide Imazalil (500ppm). H<sub>2</sub>O<sub>2</sub> provided a disinfectant effect on the pericarp, as indicated by significant reduction of total bacterial, mold and yeast counts. After cold storage and shelf-life, no significant difference was found among all treatments in the total soluble solids (TSS), titratable acid (TA), while higher vitamin C content was found in the Imazalil treated fruit. This research suggest that H<sub>2</sub>O<sub>2</sub> can be an alternative to chemical fungicides that, although more effective, pose problems due to their residue levels and health concerns, especially for the organic fruit industry.
Highlights
Because of sticky weather in south China, postharvest rotting and losses of perishable Newhall navel orange grown here are as high as 39%, which is mainly caused by P. digitatum and P. italicum, and are probably the most common postharvest disease of citrus fruits worldwide [1]
Mycelial growth of P. digitatum and P. italicum was tested by placing a 5 mm-diameter culture disc cut from the periphery of a 7-day-old mycelial mat in the center of Potato Dextrose Agar (PDA) plates supplemented with appropriate concentrations of H2O2
After 7 days of incubation, P. italicum and P. digitatum showed normal radial growth on control PDA media, while the fungicide Imazalil (500ppm) completely inhibited their radial growth, and a nearly 100% inhibition rate of P. italicum and P. digitatum was observed with H2O2 at 0.5% and 1.0% (Figure 1)
Summary
Because of sticky weather in south China, postharvest rotting and losses of perishable Newhall navel orange grown here are as high as 39%, which is mainly caused by P. digitatum and P. italicum, and are probably the most common postharvest disease of citrus fruits worldwide [1]. Long-term use of chemical fungicides in China cause pathogen resistance problem, accompanied by fungicide doses increasing and excess of fungicides residues on fruits [4]. Alternative methods for control of citrus fruit diseases are required to avoid health and environmental problems. As a sanitizer to treat the surface of fruits and vegetables against pathogenic microorganisms, Hydrogen peroxide (H2O2) has been experimentally applied for control of postharvest decay in fresh fruits [3, 5, 6]. Hydrogen peroxide is incorporated with stabilizers, such as acetic acid, silver ions, to produce a more
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