Seed biopriming and long-term air-dry storage effects on Pseudomonas fluorescens viability and Brassica napus germination

Seed biopriming with Pseudomonas fluorescence as beneficial microbial inoculant and seed hydropriming with deionised water were conducted with oilseed rape (Brassica napus). Both techniques involve restricted seed hydration followed by seed drying. Seed biopriming reduced the uniformity (time difference between 10% and 90% germination) of germination ca. 4-fold, without changing the maximum germination percentages (Gmax) of seed populations. In contrast to this, seed hydropriming improved the uniformity, but not for aged seed populations. The distinct effect of biopriming on germination was caused by the high salt concentration in the priming medium, not by the bacteria or any of the other components. The effects of biopriming duration, seed input, and temperature (incubation and drying) were tested and the number of bacteria attached to the seed coat surface was between 1.6 x 106 and 9.8 x 108 colony-forming units (CFUs) per seed. Long-term storage (21ºC, <10% relative humidity, 21% oxygen) of dry bioprimed seeds resulted in a rapid decline of bacterial viability, for example (6 h biopriming, 50 g seed input) from 9.8 x 108 CFU per seed to 7.3 x 104 after 4 weeks and 5.0 x 102 after 12 weeks of air-dry seed storage. Seed biopriming and long-term storage of dry bioprimed seeds did not affect Gmax at optimal (24ºC) and cold-stress (16ºC) temperatures, and did not appreciably affect early seedling growth. Additive biopriming with kimchi sauce did not affect the number of bacteria attached per seed, but caused an ~800-fold increase in retaining bacterial viability during long-term seed storage.