No abstract

Oxidizing compounds such as sodium hypochlorite (NaCIO) and hydrogen peroxide (H2O2) are widely used in food sanitization because of their antimicrobial effects. We applied these compounds and metals to analyze their antifungal activity against Penicillium digitatum, the causal agent of citrus green mold. The MICs were 300 ppm for NaClO and 300 mM for H2O2 when these compounds were individually applied for 2 min to conidia suspensions. To minimize the concentration of these compounds, we developed and standardized a sequential treatment for conidia that resulted in loss of viability on growth plates and loss of infectivity on lemons. The in vitro treatment consists of preincubation with 10 ppm of NaClO followed by incubation with 100 mM H2O2 and 6 mM CuSO4 (cupric sulfate). The combination of NaClO and H2O2 in the presence of CuSO4 produces a synergistic effect (fractional inhibitory concentration index of 0.36). The sequential treatment applied in situ on lemon peel 24 h after the fruit was inoculated with conidia produced a significant delay in the fungal infection. The in vitro treatment was effective on both imazalil-sensitive and imazalil-resistant strains of P. digitatum and Geotrichum candidum, the causal agent of citrus sour rot. However, this treatment inhibited 90% of mycelial growth for Penicillium italicum (citrus blue mold). These results indicate that sequential treatment may be useful for postharvest control of citrus fruit diseases.

Cerioni, L., Rapisarda, V. A., Doctor, J., Eikkert, S., Ruiz, T, Eassel, R., and Smilanick, J. L. 2013. Use of phosphite salts in laboratory and semicommercial tests to control citrus postharvest decay. Plant Dis. 97;201-212.Potassium phosphite (KP) concentrations that inhibited the germination of 50% of Pénicillium digitatum conidia were 229, 334, 360, 469, 498, or 580 mg/liter at pH 3, 4, 5, 6, 7, or 8, respectively. Increasing phosphate content in media reduced phosphite toxicity. To control green or blue mold, fruit were inoculated with P. digitatum or P. italicum, then immersed 24 h later in KP, calcium phosphite (CaP), sodium carbonate, sodium bicarbonate, or potassium sórbate for 1 min at 20 g/liter for each at 25 or 50°C. Mold incidence was lowest after potassium sórbate, CaP, or KP treatments at 50°C. CaP was often more effective than KP but left a white residue on fruit. KP was significantly Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States Department of Agriculture (USDA). USDA is an equal opportunity employer.