TABLE 3.

Expression of a phlA′-′lacZ fusion in P. fluorescens strains CHA0 and CHA638 in the wheat rhizosphere with and without F. oxysporum strain 242 or 798^a

P. fluorescens strain	F. oxysporum strain	β-Galactosidase activity (U per 108 CFU)		Plant fresh wt (g)		Bacterial rhizosphere colonization (107 CFU per g)
		Expt 1	Expt 2	Expt 1	Expt 2	Expt 1	Expt 2
None	None	nd	nd	2.7 a	2.3 a	nd	nd
	242	nd	nd	3.1 a	2.4 a	nd	nd
	798	nd	nd	3.1 a	2.7 a	nd	nd
CHA0/pME6259	None	65 a	34 a	2.6 a	2.6 a	2.7 a	1.4 a
	242	304 b	56 b	2.8 a	2.6 a	0.9 a	1.1 a
	798	38 c	22 c	2.6 a	2.6 a	1.9 a	1.1 a
CHA638/pME6259	None	460 b	287 d	2.9 a	2.6 a	2.5 a	1.5 a
	242	514 b	365 d	3.0 a	2.7 a	1.7 a	1.0 a
	798	420 b	252 d	3.0 a	2.6 a	2.4 a	0.8 a

^aP. fluorescens strains CHA0 (wild type) and CHA638 (phlF mutant) carrying a phlA′-′lacZ translational fusion on plasmid pME6259 were tested. F. oxysporum strain 242 or 798 was added to the gnotobiotic system at 10⁴ microconidia per g of soil. Plants were grown for 14 days in artificial soil under gnotobiotic conditions. Fresh weights of all plants (always five) in one flask are presented. Values represent the means of four replicate flasks with five plants each. Means within a column followed by a different letter were significantly different at P ≤ 0.05 according to Fisher's protected least significant difference test. nd, not detected.