Field trials were conducted to evaluate the season long population dynamics and location (in leaf or on leaf surface) of an antibiotic resistant strain of the bacterium Pseudomonas syringae pv. tagetis (PST) applied to Canada thistle leaves. An application preceding 2 to 3 d of hot dry weather was compared to an application preceding 2 to 3 d of cool wet weather. Leaf samples were taken weekly to assess the population of PST found inside the leaves and on the leaf surface. While PST populations initially differed, populations were similar for both treatments one week after application. While this suggests that environment did not have a major impact, weather conditions for testing this hypothesis were not ideal. Over the first 35 d of the experiment, little rainfall was observed. PST populations were low and stable. However, rain events over the 40 d that followed resulted in great oscillations in mean PST populations and in some cases significant population increases. During dry periods, internal and total PST populations differed significantly, suggesting the external populations played a major part in population composition. However, the two sampling periods that closely followed three consecutive days of rainfall indicated internal populations were not significantly different from the total, suggesting that internal populations played the primary role in population composition. The results of this research provide evidence that rain events lead to overall PST population increases and to greater proportions of PST inside Canada thistle leaves, suggesting that it is better to apply PST during wet periods than dry.

Growth chamber and field experiments were conducted to assess the potential of Pseudomonas syringae pv. tagetis (Pst) as a biocontrol agent for Canada thistle. Silwet L-77, an organosilicone surfactant, was required to facilitate Pst penetration into Canada thistle leaves. Growth chamber experiments indicated that maximum Pst populations inside leaves were obtained with a Silwet L-77 concentration of 0.3% (v/v) or greater. High Pst populations (109 colony-forming units [cfu] per gram fresh weight) were found in leaves 48 h after treatment with 108 or 109 cfu ml−1 Pst plus Silwet L-77 (0.3%, v/v). In growth chamber experiments, foliar application of Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) on 4- to 5-wk-old Canada thistle reduced shoot dry weight by 52% (measured 14 d after treatment) and chlorophyll content of emerging leaves by 92% (measured 10 d after treatment). In field trials conducted in 1999 and 2000, Pst (109 cfu ml−1) plus Silwet L-77 (0.3%, v/v) were applied at 700 L ha−1, and the method of application (paint gun, backpack sprayer, boom) and the number of applications (one or two separated by 14 d) were examined. Averaged over 2 yr, two applications with a backpack sprayer resulted in 67% disease incidence (apical chlorosis) of treated plants measured 4 wk after the initial treatment (WAIT). At the time of flower bud formation (8 WAIT), there was little or no disease incidence, 31% reduction in plant height, 81% reduction in number of flower buds, and 20% reduction in shoot survival during 1999 but no effect on survival in 2000.

Fermentation products, SCFA, particularly butyrate, are considered a sign of ‘good’ bowel health but the influence of bacterial population composition and diet on inter-individual difference in metabolites and colonic health is poorly understood. Faecal specimens were collected weekly from eight healthy human volunteers over 12 weeks. Dietary intake was self-reported and ten macronutrient factors were analysed at selected weekly periods. Faecal weight, pH and moisture were recorded, and SCFA concentrations were measured in all samples. From each specimen, DNA was prepared and eubacterial 16S rRNA gene PCR performed. Bacterial population profiles were captured by denaturing gradient gel electrophoresis (DGGE) of PCR products, and multivariate statistical analysis was performed. Faecal weight, pH and moisture varied widely within and between individuals. Average total SCFA concentrations over 12 weeks ranged from 36·9 to 144·4 mmol/kg in 48 h specimens and faecal butyrate concentrations ranged from 1·8 to 48·5 mmol/kg. Two individuals with butyrate concentrations below 10 mmol/kg were considered to be ‘low butyrate types’ and may represent an at-risk population for bowel health. Dietary fat, sugar and carbohydrate showed weak correlation with SCFA (R − 0·612, P = 0·015; R 0·607, P = 0·016; R 0·610, P = 0·016, respectively) and butyrate concentrations (R − 0·593, P = 0·02; R 0·504, P = 0·054; R 0·528, P = 0·043, respectively). Multivariate analysis of DGGE bacterial profiles demonstrated concise and repeated grouping of intra-individual samples, but these were combined with distinct inter-individual differences (analysis of similarities P < 0·001, R ≥ 0·99) The exact relationship of these SCFA values to the overall bacterial profiles and SCFA-producer bacterial groups was not direct nor linear.