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-m otile bacterium, cells applied to the germinating seed moved with the expanding root in the absence of downward water flow, and that the rat e of movement kept pace with the growing root tip in both sterilized s and and non-sterile soil. Movement in soil did not increase with incre asing water content and, in fact, the inoculant spread further and sur vived in higher numbers in the treatment at the lowest water content t ested (50% MHC; -52 kPa). However, percolating water resulted in distr ibution of the bacterium throughout the soil column and to its appeara nce in the leachate after a single water addition. Introducing P25 int o soil 1 week prior to the first water addition significantly reduced the percentage of the inoculant leached (5 vs 38%). The presence of P2 5 in the soil through which roots were growing did not increase the nu mbers 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 .