| Résumé | We have shown previously that six strains belonging to the genus Bacillus isolated from the rhizosphere of spring wheat cv. Katepwa were able to promote root growth of Katepwa but not of the parental cv. Neepawa under sterile conditions in test tubes. Further studies with strains 5A1 or 3A have shown that the growth promotion can be demonstrated under a variety of growth conditions, in sterile Leonard jars, non-sterile pots or in the field. A heat-labile factor may be involved in the mode of action because autoclaving 5A1 cells inhibited growth promotion but addition of supernatant was as effective as whole cells. IAA was detected in the supernatant using GC-MS but exogenous addition of up to 200 μg IAA per pot did not affect the growth of cv. Katepwa or Neepawa. The growth response of cv. Katepwa to inoculation with strain 5A1 was similar over a range of inoculum densities from 10⁷ to 10¹⁰ cells per pot, but the lowest density resulted in the largest growth response. A time-course experiment with strain 5A1 and cv. Katepwa indicated that growth promotion was initiated within 2 weeks of sowing, but that the growth response was not significant until 3 weeks after sowing. In the field, strain 3A increased the rate at which Katepwa seedlings emerged. Inoculation of the same cultivar with strain 5A1 increased shoot weight and tiller number by 38% (P < 0.10) and 79% (P < 0.05), respectively, 70 days after planting. Seedling emergence, shoot weight and tiller number of cv. Neepawa were not affected by inoculation with strains 5A1 or 3A. |
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