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 addedaPlant fresh wtb(mg)Root fresh wtb (mg)% Root surface infectedb,cP. fluorescensb (log CFU/g of root)
P. fluorescensT. basicola
None677 a224 a0 aND
CHA0 (wild type)681 a250 a0 a8.58 a
CHA21 (anr)616 a240 a0 a8.41 a
CHA21/pME3817 (anr +)621 a239 a0 a8.59 a
None+151 d32 d83 dND
CHA0 (wild type)+450 b152 b31 b8.98 a
CHA21 (anr)+327 c97 c58 c9.13 a
CHA21/pME3817 (anr +)+479 b175 b39 b8.80 a
  • a P. 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.

  • b Means 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.

  • c Percentage of root surface darkened by the presence of chlamydospores of T. basicola (23).