Biological control of sapstain fungi with natural products and biological control agents: a review of the work carried out in New Zealand

Colonisation of Pinus radiata sapwood by sapstain fungi results in a permanent discoloration of the sap and is one of the major problems associated with P. radiata timber production in New Zealand. No fungicides are available that can provide a reliable level of control of sapstain for the extended time period required to export timber. A 4-year survey, commencing in 1996 revealed that the most common species which cause sapstain on radiata wood are Sphaeropsis sapinea (syn. Diplodia pinea), and two species of Ophiostoma (O. floccosum and O. ips). A total of 21 different species that cause sapstain have been identified to date. Two approaches for the control of sapstain are presented in this paper. The first relies on the ability of microorganisms to inhibit the growth of sapstain species. Such an ability has been demonstrated in laboratory trials on wood chips or wood blocks for 116 isolates of the 848 fungal and bacterial isolates initially considered. Six of the most effective isolates were further tested on sawn timber or debarked logs in field trials. Isolates of Trichoderma spp. and Trichothecium roseum were found to control sapstain as well as the standard fungicide treatments. T. harzianum was significantly better in controlling sapstain in the internal tissues of debarked logs than the fungicide. The second approach is based on inhibition of the sapstain causing fungi by secondary metabolites produced by plants or microorganisms. Massoialactone, produced by various fungi including Trichoderma spp., showed good antisapstain activity in laboratory and field trials. Twenty-nine essential oils from different plant species inhibited O. piceae in the laboratory. The most efficient oils were found to contain high levels of oxygenated monoterpenes. Oxygenated alcohol or phenolic monoterpenes proved to be extremely active against sapstain fungi preventing discoloration of sapwood for up to 9 months. A method of control for sapstain based on pine oil derivatives containing some of these compounds is now being developed for commercial use.