ABSTRACT

An increasing number of studies indicate that some strains of common soil bacteria are capable of colonizing internal plant tissues. Therefore, depending on the bacterial strain, it may be necessary to monitor colonization of internal plant tissues in addition to exterior plant surfaces (Naim and Chanway, 1999). Frequent movement has also been detected with other rhizosphere-inhabitingbacteria in several plants (Lamb et al., 1996 ). Pseudomonas spp., specifically fluorescent pseudomonads, are commonly encountered (Downing and Thomson, 2000). However, it is not a universal phenomenon asP putida WCS35rr and two Pfluorescens (W CS374 and WCS374PMR) were not able to move into stems and leaves of the radishes (Raphanus sativus cv. Saxa Nova) when the seed, soil or roots had been inoculated with a bacterial suspension (Lamb et al., 1996). Movement of P aureofaciens Ps373RN Lll has been reported in the

interior of aerial tissues of all 16 plants tested and on the exterior of aerial surfaces of 15 plants. It was suggested that the bacteria might contaminate the developing shoot prior to its emergence from the soil. When inoculating the roots after shoot emergence, in either soil or hydroponic system, blocked this route, Ps373RN Lll still invaded the aerial tissues (Lamb et al., 1996).