TABLE 5.

Effect of an anr mutation in P. fluorescens CHA0 on the protection of tobacco against black root rot caused by T. basicola in a water-saturated soil under gnotobiotic conditions

Microorganism addeda		Plant fresh wtb (mg)	Root fresh wtb (mg)	% Root surface infectedb,c	P. fluorescensb (log CFU/g of root)
P. fluorescens	T. basicola
None	−	677 a	224 a	0 a	ND
CHA0 (wild type)	−	681 a	250 a	0 a	8.58 a
CHA21 (anr)	−	616 a	240 a	0 a	8.41 a
CHA21/pME3817 (anr+)	−	621 a	239 a	0 a	8.59 a
None	+	151 d	32 d	83 d	ND
CHA0 (wild type)	+	450 b	152 b	31 b	8.98 a
CHA21 (anr)	+	327 c	97 c	58 c	9.13 a
CHA21/pME3817 (anr+)	+	479 b	175 b	39 b	8.80 a

^aP. fluorescens strains and T. basicola were added at 10⁷ CFU and 5 × 10³ endoconidia per g of soil 3 and 2 days, respectively, before planting of a 5-week-old tobacco plant grown under sterile conditions. Water-saturated conditions (water content, 35%; water potential, 0 MPa) were induced 3 days after planting by adding sterile water to soil. Plants were harvested after 3 weeks. 

^bMeans within the same column followed by the same letter do not differ significantly at P = 0.05, according to Student’s t test. Data represent three individual repetitions of the same experimental setup, with eight replicates (flasks containing one tobacco plant) per treatment. ND, not detected. 

^cPercentage of root surface darkened by the presence of chlamydospores of T. basicola (23).