, 2003; Dong et al., 2003; Warriner et al., 2003) may present increased nutrient exudation, and hence may function as triggers for mobilization of S. Weltevreden to these sites (Cooley et al., 2003; Dong et al., 2003; Jablasone et al., 2005). Alternatively, S. Weltevreden may associate with the root surface through adhesive properties

(Wachtel et al., 2002), specific selective advantages (Jacobsen, 1997) and well-developed colonization ability (Dong et al., 2003), which may represent a potential strategy for contamination of plants and further dissemination selleck screening library into edible parts along the root and shoot surfaces. As the number of replicate spinach plant roots infected with S. Weltevreden increased in Experiment A during the evaluation period and bacterial numbers in individual root systems tended to increase rather than decrease over time, it is likely that the bacteria observed were viable, rather than resting or dead. In Experiment B, where S. Weltevreden was added in saline solution directly to soil after plant emergence, the pathogen was detected in all replicates at all sampling occasions (Fig. 3). However, bacterial numbers present in the roots decreased significantly from day 0 to day 21 postinoculation, in contrast to the trend of increased cell numbers with time in Experiment

A. When roots started to develop in the pots in Experiment A, S. Weltevreden may have benefited from increased nutrient levels

available in roots accessible via lateral root junctions or breaks, leading to proliferation. The MG-132 more pronounced decline in bacterial numbers in roots in Experiment B, compared with Experiment A, was similar to the trends seen in soil between the two 4��8C experiments. This indicates that S. Weltevreden inoculated into soil after plant emergence faced more competition from the indigenous microbial communities for nutrients and colonization sites compared with S. Weltevreden applied to the soil before planting. Salmonella can contaminate crops in fields through leaves or other aerial surfaces (Doyle & Erickson, 2008). In the current study, no S. Weltevreden cells were recovered above the threshold level on leaves when added to the soil in a manure mixture (Experiment A). However, when bacteria were added in saline solution and added directly to soil 14 days after sowing and fertilization, cells were detected in all replicate pots on days 0 and 7 postinoculation (Experiment B). However, as S. Weltevreden was detected on leaves on the day of bacterial addition, this finding may have been an artifact resulting from negligent inoculation, i.e. unintentional application of bacteria to the leaves. Alternatively, S. Weltevreden may have potentially mobilized to spinach leaves through direct contact between leaves and soil/manure slurry as well as aerosol dispersion (Doyle & Erickson, 2008). Nevertheless, it is interesting to note that S.