Inhibition of growth in canola seedlings caused by an opportunistic Pseudomonas sp. Under laboratory and field conditions

Abstract

If Pseudomonas rp2, a field-isolated fluorescent pseudomonad, is present on canola (rape) seeds at the time of sprouting, it causes an inhibition of root growth leading to death or delayed maturation of the plant. Inhibitory strains of this type comprise less than 10% of the fluorescent pseudomonads isolated from local field samples, but they were found in widely dispersed sources. By present standards, these Pseudomonas strains would be considered soil saprophytes, since they survive in sterile soil at 4 and −20 °C in the absence of plant material, and since they do not match taxonomically with established plant pathogenic Pseudomonas spp. tested. Under laboratory conditions, inoculation of seeds with Pseudomonas rp2 caused death in 30%, and delayed development in 68% of infected plants. Minimum bacterial load, recoverable from the seed surface and capable of causing inhibition, was 10–20 colony-forming units per seed. The effect of inoculation of seeds with Pseudomonas rp2 on stand, rate of growth, and seed yield was quantitated under field conditions. The results reflected values obtained under laboratory conditions. The potential economic and ecological significance of this type of infection is discussed.