Identification of Pseudomonas Spp. That Increase Ornamental Crop Quality During Abiotic Stress

Abstract

The sustainability of ornamental crop production is of increasing concern to both producers and consumers. As resources become more limited, it is important for greenhouse growers to reduce production inputs such as water and chemical fertilizers, without sacrificing crop quality. Plant growth promoting rhizobacteria (PGPR) can stimulate plant growth under resource-limiting conditions by enhancing tolerance to abiotic stress and increasing nutrient availability, uptake, and assimilation. PGPR are beneficial bacteria that colonize the rhizosphere, the narrow zone of soil in the vicinity of the roots that is influenced by root exudates. In this study, in vitro experiments were utilized to screen a collection of 44 Pseudomonas strains for their ability to withstand osmotic stress. A high-throughput greenhouse experiment was then utilized to evaluate selected strains for their ability to stimulate plant growth under resource-limiting conditions when applied to ornamental crop production systems. The development of a highthroughput greenhouse trial identified two pseudomonads, P. poae 29G9 and P. fluorescens 90F12-2, that increased petunia flower number and plant biomass under drought and low-nutrient conditions. These two strains were validated in a productionscale experiment to evaluate the effects on growth promotion of three economically important crops: Petunia × hybrida, Impatiens walleriana, and Viola × wittrockiana. Plants treated with the two bacteria strains had greater shoot biomass than untreated control plants when grown under low-nutrient conditions and after recovery from drought stress. Bacteria treatment resulted in increased flower numbers in drought-stressed P. hybrida and I. walleriana. In addition, bacteria-treated plants grown under low-nutrient conditions had higher leaf nutrient content compared to the untreated plants. Collectively, these results show that the combination of in vitro and greenhouse experiments can efficiently identify beneficial Pseudomonas strains that increase the quality of ornamental crops grown under resource-limiting conditions.

Isolation of Rhizosphere Bacteria That Improve Quality and Water Stress Tolerance in Greenhouse Ornamentals

“…An in vitro osmoadaptability bioassay was conducted according to Nordstedt et al (2020) for the selection of the most osmotic stress tolerant bacteria within the greenhouse rhizosphere collection. Briefly, a sterile 96-well microplate replicator (Boekel Scientific, Feasterville, PA, United States, Model 140500) was used to transfer glycerol freezer stocks of each isolate into separate wells of a 96-well microtiter plate pre-filled with 200 µL Luria-Bertani (LB) media for inoculation.…”

“…Each bacterial isolate was assayed on three separate microtiter plates (n = 3). Strains Pseudomonas poae 29G9 and Pseudomonas fluorescens 90F12-2 were used for comparison, because they were previously reported to withstand osmotic stress and increase plant tolerance to abiotic stress (Nordstedt et al, 2020). Plates were incubated at 28 • C with shaking at 120 r/min.…”

“…A high-throughput greenhouse trial pipeline developed by Nordstedt et al (2020) was used for the in planta evaluation of the in vitro-selected osmoadaptive and ACC deaminase-producing bacteria. The bacteria were evaluated for their ability to stimulate growth of Petunia × hybrida 'Picobella Blue' under water stress conditions.…”

“…In particular, the application of PGPR in ornamental plant production can be used to enhance plant stress tolerance and increase plant health and quality under water deficient conditions. Recent studies have shown that the application of different PGPR can enhance plant quality by increasing plant size and flower number in greenhouse ornamental species when grown under normal conditions or subjected to abiotic stress (Göre and Altin, 2006;Flores et al, 2007;Hoda and Mona, 2014;Leoni et al, 2019;Nordstedt et al, 2020). However, to positively influence the quality of plants subjected to abiotic stress, the PGPR must first induce physiological changes that increase plant stress tolerance, allowing the plant to better overcome the stress during recovery (Yang et al, 2009).…”

“…The bacteria were isolated from the rhizosphere of plants grown in controlled environment greenhouse systems and subjected to severe water deficit. The isolated bacteria were screened using a previously established pipeline (Nordstedt et al, 2020) and then evaluated for their ability to improve the growth, quality, and overall health of two economically important ornamental plant species.…”