From Seed to Salad: Impacts of ACC Deaminase-Containing Plant Growth Promoting Rhizobacteria on Lettuce Growth and Development

Many plant growth promoting rhizobacteria (PGPR) containing the enzyme ACC deaminase (ACCd) stimulate root (and shoot) growth by decreasing plant production of the plant hormone ethylene, which is often inhibitory to growth. The potential for incorporating ACCd-containing PGPR in vegetable transplant production was evaluated in a Lactuca sativa (lettuce)-Variovorax paradoxus 5C-2 combination. Effects of V. paradoxus 5C-2 were restricted to early growth stages: primary root growth was enhanced (15%) in filter paper culture and three weeks after seedling transplant to the field, biomass accumulation was greater (37%) in drying soil. These effects were not apparent in longer-term field trials, or in greenhouse pot trials, but did not seem to be related to the level of colonization of V. paradoxus 5C-2 on lettuce roots. Future experiments with this plant: bacterial combination should occur in unfavourable growing conditions known to stimulate ethylene evolution and inhibit growth.