Potassium silicate: a new organic tool for the control of citrus postharvest green mold

Abstract

Since 2010, potassium silicate (PSi, K2SiO3) is included in the list of synthetic substances allowed for use in organic crop production in the USA. Thus, the curative activity of postharvest treatments with PSi against one of the most economically important citrus postharvest diseases, green mold caused by the fungus Penicillium digitatum, was evaluated in laboratory trials. Oranges (Citrus sinensis L. 'Lane Late') were artificially inoculated in rind wounds with the pathogen and 24 h later immersed in aqueous solutions of 90 mM PSi at 20 or 50°C for 60 or 150 s. This PSi concentration was selected as the most effective in previous in vivo primary screening tests. Treated fruit were incubated for 7 days at 20°C, and then disease incidence (% of infected wounds) and severity (lesion diameter) were recorded. Dips at 20°C for 60 s were selected as the most effective and practical treatment conditions. These treatments were then applied to 'Valencia' oranges inoculated 24 h before and subsequently stored at 5°C and 90% RH for up to 6 weeks. Control fruit were dipped in water. At the end of the cold storage, PSi dips significantly reduced the incidence of green mold by 45% with respect to control fruit. Lesion diameter at the end of the cold storage was 200 and 98 mm on control and PSi-treated oranges, respectively. In conclusion, postharvest PSi treatment showed potential as a new reduced-risk chemical treatment for cost-effective control of citrus green mold. It can be of use in integrated disease management programs to replace or reduce the use of conventional postharvest fungicides.