Growth Promoting of Some Ornamental Plants by Root Treatment with Specific Fluorescent Pseudomonads

Beneath the blooms: Unearthing the effect of rhizospheric bacteria on floral signals and pollinator preferences

The relationship between plants and pollinators is known to be influenced by ecological interactions with other community members. While most research has focused on aboveground communities affecting plant-pollinator interactions, it is increasingly recognized that soil-dwelling organisms can directly or indirectly impact these interactions. Although studies have examined the effects of arbuscular mycorrhizal fungi on floral traits, there is a gap in research regarding similar effects associated with plant growth-promoting rhizobacteria (PGPR), particularly concerning floral scent. Our study aimed to investigate the influence of the PGPR Bacillus amyloliquefaciens on the floral traits of wild (Solanum habrochaites, Solanum pimpinellifolium and Solanum peruvianum) and cultivated tomato (Solanum lycopersicum), as well as the impact of microbially-driven changes in floral scent on the foraging behaviour of the stingless bee Melipona quadrifasciata. Our findings revealed that inoculating tomatoes with PGPR led to an increased number of flowers and enhanced overall floral volatile emission. Additionally, we observed higher flower biomass and pollen levels in all species, except S. peruvianum. Importantly, these changes in volatile emissions influenced the foraging behaviour of M. quadrifasciata significantly. Our results highlight the impact of beneficial soil microbes on plant-pollinator interactions, shedding light on the multiple effects that plant-microbial interactions can have on aboveground organisms.

Insect exuviae as soil amendment affect flower reflectance and increase flower production and plant volatile emission

Soil composition and herbivory are two environmental factors that can affect plant traits including flower traits, thus potentially affecting plant-pollinator interactions. Importantly, soil composition and herbivory may interact in these effects, with consequences for plant fitness. We assessed the main effects of aboveground insect herbivory and soil amendment with exuviae of three different insect species on visual and olfactory traits of Brassica nigra plants, including interactive effects. We combined various methodological approaches including gas chromatography/mass spectrometry, spectroscopy and machine learning to evaluate changes in flower morphology, colour and the emission of volatile organic compounds (VOCs). Soil amended with insect exuviae increased the total number of flowers per plant and VOC emission, whereas herbivory reduced petal area and VOC emission. Soil amendment and herbivory interacted in their effect on the floral reflectance spectrum of the base part of petals and the emission of 10 VOCs. These findings demonstrate the effects of insect exuviae as soil amendment on plant traits involved in reproduction, with a potential for enhanced reproductive success by increasing the strength of signals attracting pollinators and by mitigating the negative effects of herbivory.

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

Water deficit stress is a major contributor to the loss of ornamental crop value due to its negative effects on plant growth and flowering. In addition, post-production water stress can reduce the photosynthetic capacity of plants, negatively impacting crop quality at retail and in the consumer's home and garden. While the application of microbe-containing biostimulant products can increase stress tolerance and crop quality, the success of most commercially available biostimulants in greenhouse production systems is inconsistent. To identify beneficial bacteria with consistent biostimulant activity in greenhouse ornamentals, our study isolated bacteria from the rhizosphere of water stressed greenhouse ornamentals. Five species of popular ornamentals were obtained from 15 different commercial greenhouse facilities and then subjected to three cycles of water stress. Over 1,000 bacterial isolates were collected from the rhizosphere and screened in vitro for osmoadaptability and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Eighty selected isolates were evaluated in a high-throughput greenhouse trial for their ability to increase plant size and flower number of water-stressed Petunia × hybrida. Ten bacterial strains selected from the high-throughput trial were then evaluated in a greenhouse validation trial for their ability to increase plant growth and to mitigate the reduction in photosynthetic parameters of water stressed P. hybrida and Pelargonium × hortorum. Application of certain bacteria increased plant size in both species and flower number of P. hybrida after recovery from water stress when compared to untreated water stressed plants. In addition, bacteria application increased the chlorophyll fluorescence parameters including quantum yield and efficiency of photosystem II (PSII) and electron transport rate (ETR), while decreasing the extent of electrolyte leakage during water stress and recovery. Overall, this study identified bacterial strains that can increase tolerance to and recovery from water stress in two commercially important ornamental crop species.

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

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 high-throughput 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 production-scale 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.