5.2.83
THE POTENTIAL FOR BIOLOGICAL CONTROL OF BLUESTAIN IN BRITAIN

CS JONES1, JF WEBBER1 and DJ DICKINSON2

1Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH, UK; 2Imperial College, Prince Consort Road, London SW7 1BB, UK

Background and objectives
The saw milling and paper milling industries experience serious economic losses every year due to the action of wood-degrading bluestain fungi. Freshly felled timber is particularly susceptible to colonisation by these fungi, mainly from the order Ophiostomatales; the subsequent dark blue or brown stain they produce causes only cosmetic damage but markedly reduces the value of the timber. Currently, stain is controlled by minimising timber storage time, kiln drying and the use of chemical treatments. However, growing environmental concern about the use of chemicals means biological controls are of increasing interest. Cartapip is a biological agent which is currently marketed in North America. It is a colourless form of the bluestain fungus Ophiostoma piliferum which, if applied to freshly felled timber, has the potential to exclude pigmented bluestain fungi, thus preventing discoloration from occurring [1]. Reports indicate that the albino nature of Cartapip is due to a naturally occurring mutation in the melanin synthesis pathway genes [2]. Although Cartapip is registered with the US Environmental Protection Agency as a pitch control agent, in Britain the main commercial application of Cartapip is likely to be as a biological control of stain in conifer, particularly pine, wood. Thus there is interest in whether the Cartapip form of O. piliferum, which originates from North America, will be effective on the pine species grown in Britain (mainly Pinus sylvestris and P. nigra); how it will interact with native European fungi including pigmented individuals of O. piliferum; whether it will be able to exclude indigenous bluestainers effectively and whether the albino nature of Cartapip is linked to reduced fitness.

Materials and methods
The conspecificity of pigmented individuals of O. piliferum from both North America and Europe was tested in mating experiments which included Cartapip. The competitive abilities of Cartapip and the most commonly occurring bluestain fungi were evaluated by measuring growth rates in culture at a range of temperatures, by observing their ability to colonise freshly felled pine and determining the effectiveness of Cartapip to protect freshly felled pine from naturally occurring bluestain inocula.

Results and conclusions
Crosses between UK O. piliferum isolates and those of North American origin were fully fertile when isolates of compatible mating type were paired. However, one mating type (A) dominated the UK sample, whereas the two mating types (A and B) occurred at a similar frequency in the sample of North American isolates. Cartapip mated with both UK and North American isolates of opposite mating type (A) providing it acted as the male, but was female sterile when acting as the recipient. Analysis of the progeny from Cartapip and pigmented O. piliferum crosses suggested several genes affected pigmentation, but albino progeny were usually the same mating type as their colourless parent, indicating that pigmentation and mating type loci were linked. In general, UK isolates of O. piliferum grew optimally in culture at 27.5C and were faster growing than those from North America. The exception was Cartapip which, overall, was one of the fastest-growing isolates between 22.5 and 30C. It proved to be an effective coloniser in freshly felled pine logs (P. sylvestris) growing faster than the pigmented O. piliferum, although other bluestain fungi (Ceratocystis coeruiescens, O. minus, Sphaeropsis sapinea) were significantly faster growing. Finally, a brush or spray application of Cartapip spores to the ends of pine logs gave similar levels of bioprotection, but it did not exclude all sapstainers. In both control- and Cartapip-treated logs S. sapinea was found to have invaded the logs from the cut ends. Applications of Cartapip did, however, reduce the amount of staining compared to the controls. This suggests that Cartapip is effective at colonising pine in the UK, but its performance must be enhanced for successful biocontrol. Improved control using Cartapip and native colourless bluestain species is currently being evaluated.

References
1. Behrendt CJ, Blanchette RA, Burnes TA, Farrell RL, 1995. Phytopathology 85, 92-97.
2. Zimmerman WC, Blanchette RA, Farrell RL, 1995. Mycologia 87, 857-863.