FACTORS INFLUENCING THE CONTROL OF PYTHIUM-ULTIMUM INDUCED SEED DECAY BY SEED TREATMENT WITH PSEUDOMONAS-AUREOFACIENS AB254

Emergence of sh-2 sweet corn seedlings from soil infested with Pythium ultimum at three diverse field sites was greatly improved either by coating the seed with Pseudomonas aureofaciens AB254, or by bio-priming the seed with this bacterium. Both treatments were equivalent to the control provided by treating the seed with the fungicide metalaxyl. In controlled-environment tests, emergence of sweet corn seedlings in soil that was autoclaved or naturally infested with P. ultimum increased with soil temperature from 5 to 24-degrees-C. Low soil temperatures enhanced the impact of P. ultimum on sweet corn seed, with the most severe decay of untreated seed at soil temperatures between 5 and 17-degrees-C. Bio-priming and seed coating with P. aureofaciens AB254 increased seedling emergence compared with that of untreated seed at all temperatures, even though bacterial multiplication did not occur at low temperatures. Increasing P. ultimum inoculum density from 0 to >1800 propagules per gram (p.p.g.) decreased emergence from untreated seed from 90 to 11%. There was no corresponding reduction in emergence in soil with inoculum densities >159 p.p.g. when the seed was bio-primed or coated with bacteria. Decay was more severe with increasing soil water potential from -0.07 to -0.01 MPa. At low and intermediate soil moisture, both bio-priming and bacterization with P. aureofaciens AB254 improved seedling emergence compared with untreated seed, but at the highest soil moisture only the bio-priming treatment provided protection.