Data were analysed using analysis of variance methods in Minitab (Minitab Inc.). To identify significant differences between groups the General Linear Model (GLM) procedure, followed by Tukey’s multiple pair-wise comparison tests were applied. P values of less than 5% were considered statistically significant. Where appropriate data were log transformed prior to analysis. Group means were plotted to show means and their standard errors, and the size of treatment effects were estimated using differences between group means and their 95% confidence intervals.