Damping-off Oomycetes in natural regeneration of Scots Pine
Phytophthora cinnamomi var. cinnamomi, Pythium ultimum var. ultimum and Pythium undulatum were successfully isolated from naturally regenerating Pinus sylvestris forests across north Scotland. Molecular and morphological characterisation enabled accurate identification of these Oomycetes to the variety level. In vitro and glasshouse pathogenicity trials demonstrated that under artificial temperature, light and water regimes the Oomycetes had the potential to reduce plant growth and cause chlorosis of the P. sylvestris foliage after two months. Soil pH was also determined as having a significant effect on P. sylvestris growth in terms of foliage colour and dry mass. Biological control in vitro experiments with Bacillus subtilis and Pseudomonas fluorescens produced significant inhibition of Oomycete growth but on transfer to the glasshouse trials, antagonism was not observed. This study was undertaken to establish the presence of fine root pathogens, namely those belonging to the Oomycetes, within regenerating Pinus sylvestris forests in northern Scotland. The identify of the pathogens was determined using morphological and molecular biology techniques. The virulence of the fine root pathogens on Pinus sylvestris seedlings (1 + 0) was then determined by a series of in vitro and glasshouse trials. Interactions between soil pH and bacterial biological control agents were also tested against each of the pathogens. Pathogen trials were undertaken to show the potential effect of the Oomycetes on Pinus sylvestris seedlings. The glass house trial was scored on foliage colour and dry weight of seedlings 18 months of age, grown in pH amended Irish moss peat. In comparison to the control, inoculation with P. cinnamomi caused a significantly greater frequency of chlorotic/dead seedlings. In contrast, inoculation with P. undulatum (syn. P. dimorphum) resulted in a greater number of healthy seedlings than the control. No significant difference in the proportion of healthy and chlorotic/dead seedlings was found between the bio-control bacteria groups. pH was found to have a significant effect on seedling growth. At pH 7, compared to pH 3, there was a significant greater likelihood of the seedlings being chlorotic/dead.