2019 ASHS Annual Conference

Low nutrient and post-harvest drought stress are two of the most limiting factors to ornamental crop quality; causing stunted growth and reduced flowering. Plant growth promoting rhizobacteria (PGPR) have the ability to stimulate plant growth during abiotic stress by enhancing macro- and micronutrient uptake, increasing the production of plant growth-promoting hormones, and reducing stress hormones like ethylene. Previous work has identified three Pseudomonas strains that can increase flower number and shoot biomass when applied to Petunia × hybrida ‘Picobella Blue’. These three strains were then validated in a production scale experiment to evaluate the effects on growth promotion in P. hybrida ‘Picobella Blue’, Impatiens walleriana ‘Super Elfin Ruby’, and Viola × wittrockiana ‘Delta Pure Red’. A low nutrient experiment was conducted with plants grown under constant fertigation with 25 mg L^-1 N from 15-5-15 CaMg and treated with each of the three bacteria strains: P. vranovensis 15D11, P. poae 29G9, and P. fluorescens 90F12-2. In a second experiment plants were treated with each of the three bacteria strains and then subjected to drought stress five weeks after transplant. Negative controls for both experiments included application of uninoculated LB media. Plants were grown to the marketable stage and flower number and shoot biomass was recorded as an indicator of plant growth promotion. Application of each of the three strains resulted in an increase in shoot biomass of all three bedding plant species under both drought and low nutrient conditions compared to the negative control. I. walleriana plants grown under low nutrient conditions had higher leaf nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium content compared to the untreated plants (i.e. negative control). All three bacteria strains also significantly increased flower number of P. hybrida after recovery from the drought stress. This work provides an efficient method to select and validate bacteria for their ability to increase floriculture crop quality under different abiotic stresses.