ROOT COLONIZATION BY A FLAVOBACTERIUM SPECIES AND THE INFLUENCE OF PERCOLATING WATER

The colonization of wheat roots by Flavobacterium P25 was investigated in small scale microcosms. It was shown that, although P25 is a non-motile bacterium, cells applied to the germinating seed moved with the expanding root in the absence of downward water flow, and that the rate of movement kept pace with the growing root tip in both sterilized sand and non-sterile soil. Movement in soil did not increase with increasing water content and, in fact, the inoculant spread further and survived in higher numbers in the treatment at the lowest water content tested (50% MHC; -52 kPa). However, percolating water resulted in distribution of the bacterium throughout the soil column and to its appearance in the leachate after a single water addition. Introducing P25 into soil 1 week prior to the first water addition significantly reduced the percentage of the inoculant leached (5 vs 38%). The presence of P25 in the soil through which roots were growing did not increase the numbers of P25 on the root. However, by the final sampling date (t = 30 days), P25 populations on lower root sections were greater (95 x at 8-12 cm, 389 x at 12-16 cm and 17.9 x at 16-20 cm) in percolated columns.