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

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 °C and 90% RH for 7 d or stored at 5 °C and 90% RH for 8 weeks plus 7 d of shelf-life at 20 °C. Effective concentrations were selected in in vivo primary screenings with ‘Valencia’ oranges. SMP at 200 mM was tested at 20, 50 or 62 °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 °C for 60 s were selected and applied alone or in combination with 25 μL L−1 of the conventional fungicide imazalil (SMP + IMZ 25). Imazalil at the very low concentrations of 25 (IMZ 25) or 50 μL L−1 (IMZ 50) were also tested. Effectiveness of SMP alone at 20 °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 °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 °C and 7 d at 20 °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 °C for 60 s did not prevent GM on ‘Valencia’ oranges wounded, treated, inoculated with P. digitatum 24 h later, and incubated at 20 °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.

► SMP showed curative activity against green and blue molds on citrus fruit. ► Dips of 200 mM SMP at 20 °C for 60 s were selected as the most suitable treatments. ► Heating SMP solutions did not enhance their effectiveness. ► SMP was compatible with low doses of the fungicide imazalil. ► SMP controlled the molds more effectively on oranges than on mandarins.