Effects of seed inoculation with a strain of Pseudomonas fluorescens on root growth and activity of wheat in well-watered and drought-stressed glass-fronted rhizotrons

Identification of mechanisms by which plant growth-promoting rhizobacteria (PGPR) affect plants is required to obtain consistent or predictable increa ses in crop yields using PGPR. We conducted an outdoor lysimeter study usin g 12 glass-fronted rhizotrons to determine if inoculation with a strain of Pseudomonas fluorescens (G20-18) might benefit spring wheat (Triticum aesti vum L.) (cv. Katepwa) yield by altering root growth. Inoculated and uninocu lated treatments were either well watered or subjected to terminal drought with just one surface irrigation at anthesis. The only significant effect o f G20-18 inoculation was a reduction in root growth in the well-watered rhi zotrons after about 40 d. Inoculation did not significantly affect depth of rooting, soil moisture depletion, seed yield or uptake of N-15-labelled fe rtilizer. Watering regime did not affect overall root growth, although ther e were significant differences within specific depths. Final yields in well -watered treatments were double those of the drought-stressed treatments. V ariability in yields within the drought-stressed treatments occurred due to accidental flooding of several rhizotrons early in the experiment, and dem onstrated the value of deeply placed available moisture under drought condi tions. We conclude that inoculation with G20-18 has minor effects on root g rowth that are unlikely to affect wheat yield.