Characterization of postharvest treatments with sodium methylparaben to control citrus green and blue molds

Abstract

The curative antifungal activity of postharvest sodium methylparaben (SMP) treatments against citrus green (GM) and blue (BM) molds was characterized on different citrus species and cultivars artificially inoculated with Penicillium digitatum or Penicillium italicum and incubated at 20 degrees C and 90% RH for 7 d or stored at 5 degrees C and 90% RH for 8 weeks plus 7 d of shelf-life at 20 degrees C. Effective concentrations were selected in in vivo primary screenings with 'Valencia' oranges. SMP at 200 mM was tested at 20, 50 or 62 degrees C for 30,60 or 150 s in small-scale trials to determine the best dip treatment conditions. Dips of 200 mM SMP at 20 degrees C for 60 s were selected and applied alone or in combination with 25 mu L L-1 of the conventional fungicide imazalil (SMP + IMZ 25). Imazalil at the very low concentrations of 25 (IMZ 25) or 50 mu L L-1 (IMZ 50) were also tested. Effectiveness of SMP alone at 20 degrees C for 60 s was significantly higher on oranges (cvs. 'Valencia' and 'Lanelate') than on mandarins (cvs. 'Clemenules', 'Nadorcott' and 'Ortanique'), with GM and BM incidence reductions of up to 88% after 7 d at 20 degrees C. SMP was compatible with IMZ 25 and consistently improved its performance, irrespective of citrus cultivars and storage conditions. All treatments were less effective on 'Clemenules' mandarins. On 'Valencia' oranges stored for 8 weeks at 5 degrees C and 7 d at 20 degrees C, the combined treatment was significantly more effective than the single treatments (reductions of GM and BM incidence of about 50-60% and 90-95%, respectively). In additional tests, 200 mM SMP dips at 20 degrees C for 60 s did not prevent GM on 'Valencia' oranges wounded, treated, inoculated with P. digitatum 24h later, and incubated at 20 degrees C for 7 d. In contrast, the treatments IMZ 25 and SMP + IMZ 25 showed significant preventive activity. It can be concluded from these results that SMP aqueous solutions, especially applied at room temperature, might be an interesting nonpolluting control alternative to be included in citrus postharvest disease control programs in the future. (C) 2012 Elsevier B.V. All rights reserved.