Title : Identifying beneficial bacteria that enhance abiotic stress tolerance in horticulture crops
Abstract:
Plant growth promoting bacteria can enhance growth and stress tolerance by improving the efficiency of nutrient uptake, producing plant growth promoting hormones, or reducing stress hormones like ethylene. Nutrient deficiencies and drought stress can have a negative impact on horticultural crop quality and yield. The application of beneficial bacteria in greenhouse production systems can increase stress tolerance under low water and nutrient conditions, and allows for the production of high quality crops with lower fertilizer inputs. A collection of 45 known Pseudomonas strains and a core lab collection of 1,100 bacteria isolates were screened using multiple in-lab assays to identify bacteria with the potential to enhance plant growth and stress tolerance. Polyethylene glycol (PEG) was used for the in vitro selection of osmotic stress tolerant bacteria, a trait correlated with the ability to alleviate drought stress in plants. The second bioassay identified bacteria that produce the enzyme 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase. ACC deaminase is capable of reducing the amount of stress ethylene produced by plants by degrading the ethylene precursor, ACC. Bacteria with the ability to solubilize organic phosphorus and potentially increase nutrient availability to plants were selected in a third assay. These three independent in-lab assays led to the selection of over 200 bacteria that were evaluated in greenhouse trials. Petunias were treated weekly by drenching the growing media with an equal concentration of bacteria. Young plants (two weeks after transplant) had water withheld until plants were severely wilted. Plants were then irrigated and recovery was assessed. Shoot biomass and flower number were measured to determine differences in the growth of bacteria-treated plants and untreated control plants. Petunias were also grown under nutrient deficient conditions to identify bacteria that could enhance plant growth above that of the untreated control (no bacteria) plants. Elite bacteria strains that promoted growth in greenhouse trials under both drought and low nutrient conditions were identified. Isolates selected from the core collection will be sequenced, and in addition to the known Pseudomonas strains, this information will be used to develop future experiments to investigate the potential modes of action for growth promotion under abiotic stress.
