Sanitation of a South African forestry nursery contaminated with Fusarium circinatum using hydrogen peroxide at specific oxidation reduction potentials

Abstract

Pitch canker, caused by Fusarium circinatum, was first reported in a forestry nursery in the Mpumalanga Province of South Africa in 1990, and it has since spread to almost all forestry nurseries in the country, where it causes significant economic losses. The aim of the current study was to (i) identify sources of F. circinatum contamination in the Karatara forestry nursery in the Western Cape Province and (ii) manage the disease by implementing an oxidation reduction potential (ORP)-based sanitation method using hydrogen peroxide. The irrigation water, planting tray inserts and seeds were screened for fungal contamination. Fusarium circinatum colonies were identified morphologically and confirmed by polymerase chain reaction using speciesspecific primers. Both the irrigation water and planting tray inserts served as sources of inoculum that introduced the pathogen into the nursery. The irrigation water was amended with hydrogen peroxide at an ORP level of 400 mV for an exposure time of 6 h because it was observed that such a treatment effectively killed all F. circinatum spores and was not phytotoxic to pine seedlings under laboratory conditions. In addition, the contaminated planting tray inserts were cleaned in water amended with hydrogen peroxide at an ORP value of 360 mV for 6 h, which was shown to efficiently eliminate all inoculum from planting tray inserts. Since the introduction of the ORP-based sanitation method at Karatara nursery, losses of pine seedlings were reduced to insignificant levels, and field losses were minimized.