Allium cepa L. Inoculation with a Consortium of Plant Growth-Promoting Bacteria: Effects on Plant Growth and Development and Soil Fertility Status and Microbial Community

Abstract

The present work was aimed at investigating the effects of a four strains consortium—Azospirillum brasilense, Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, and Burkholderia ambifaria—on crops of Allium cepa L. and its soil health. The bacterial consortium was inoculated on seeds of two different onion varieties; inoculated seeds and control ones (treated with autoclaved inoculum) were sown in open-field and followed until harvest. Plant growth development parameters, as well as soil physico-chemical and molecular profiles (DNA extraction and 16S community sequencing on the Mi-Seq Illumina platform), were investigated. The results showed a positive influence of bacterial application on plant growth, with increased plant height (+18%), total chlorophylls (+42%), crop yields (+13%), and bulbs dry matter (+3%) than the control. The differences between control and treated experimental conditions were also underlined in the bulb extracts in terms of total phenolic contents (+25%) and antioxidant activities (+20%). Soil fertility and microbial community structure and diversity were also positively affected by the bacterial inoculum. At harvest, the soil with the presence of the bacterial consortium showed an increase of total organic carbon, organic matter, and available P and higher concentrations of nutrients than control. The ecological indexes calculated on the molecular profiles showed that community diversity was positively affected by the bacterial treatment. The present work allowed to remark the effective use of plant growth-promoting bacteria as a valid fertilization strategy to improve yield in productive landscapes, whilst safeguarding soil biodiversity.

Bacterial Plant Biostimulants: A Sustainable Way towards Improving Growth, Productivity, and Health of Crops

“…PGPR formulations are a significant biostimulant class, as they allow root growth, mineral availability, and efficiencies in the utilization of nutrients in the crop rhizosphere to increase crop growth [45]. Many PGPR are known to stimulate phytohormone production through a combination of various mechanisms [46][47][48][49][50][51][52][53] represented in Table 2.…”

The Application of Arbuscular Mycorrhizal Fungi as Microbial Biostimulant, Sustainable Approaches in Modern Agriculture

“…Various notable protective mechanisms in the utilization of microbial biostimulants under different stresses are osmolite production, phytohormone level modulation, increased antioxidant activity, and secretion of extracellular polymeric substances (EPS) under water stress such as flooding and drought [129][130][131]; phytohormone level modulation, emission of volatile organic components, ice nucleation activity antagonism, delay of senescence, and osmo and thermal protection under thermal stress such as freezing and extreme heat [132][133][134][135]; increased soil exploration and mineral nutrient solubilization under nutrient stress [136,137]; and induced system resistance, direct antagonism with pathogens, and phytohormone level modulation under biotic stress [138][139][140][141][142]. Bozhinova [143] reported that the application of the microbial inoculant Europlus ® and the protein hydrolysate (PH) Trainer ® increased the yield of tobacco by 5.5% and 6.7%, respectively, in comparison with untreated plants.…”