Plant Growth-Promoting Bacteria: Biotic Strategy to Cope with Abiotic Stresses in Wheat

Impact of PGPR inoculation on root morphological traits and root exudation in rapeseed and camelina: interactions with heat stress

Root exudation is involved in the recruitment of beneficial microorganisms by trophic relationships and/or signalling pathways. Among beneficial microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are known to improve plant growth and stress resistance. These interactions are of particular importance for species that do not interact with mycorrhizal fungi, such as rapeseed (Brassica napus L.) and camelina (Camelina sativa (L.) Crantz). However, heat stress is known to have a quantitative and qualitative impact on root exudation and could affect the interactions between plants and PGPR. We aimed to analyse the effects of PGPR inoculation on root morphology and exudation in rapeseed and camelina at the reproductive stage. The modulation of the effects of these interactions under heat stress was also investigated. The plants were inoculated twice at the reproductive stage with two different Pseudomonas species and were exposed to heat stress after the second inoculation. In non-stressing conditions, after bacterial inoculation, rapeseed and camelina exhibited two contrasting behaviours in C root allocation. While rapeseed plants seemed to suffer from the interactions with the bacteria, camelina plants appeared to control the relationship with the PGPR by modifying the composition of their root exudates. Under heat stress, the plant-PGPR interaction was unbalanced for rapeseed, for which the C allocation strategy is mainly driven by the C cost from the bacteria. Alternatively, camelina plants prioritized C allocation for their own above-ground development. This work opens up new perspectives for understanding plant-PGPR interactions, especially in an abiotic stress context.

Plant growth-promoting bacteria as affected by N availability as a suitable strategy to enhance the nutritional composition of lamb's lettuce affected by global warming

Heat and nutritional stresses have a significantly effect on the accumulation of bioactive and other compounds harmful to human health, like nitrates, in green leafy vegetables like lamb's lettuce. Plant growth-promoting bacteria (PGPB) have shown to confer beneficial biochemical changes to various crops under different stresses. The hypothesis proposed here is that the combination of optimal N level (2.5 Mm, 12 mM or 20 mM of N) with the inoculation of PGPB in plants exposed to heat shock (43 °C) may be a good strategy to obtain healthier lamb's lettuce with a higher yield. Results showed that a dose of 20 mM N can be considered as overfertilization. Moreover, the inoculation of plants fed with fertilizers with reduced N and under heat stress, resulted in higher productivity and content of sugars (60 %), amino acids (94 %), nitrogen (21 %), and total phenolic compounds (30 %), and a reduced content of nitrates (27 %).

Plant Development of Early-Maturing Spring Wheat (Triticum aestivum L.) under Inoculation with Bacillus sp. V2026

The effect of a plant growth-promoting bacterium (PGPB) Bacillus sp. V2026, a producer of indolyl-3-acetic acid (IAA) and gibberellic acid (GA), on the ontogenesis and productivity of four genotypes of early-maturing spring wheat was studied under controlled conditions. The inoculation of wheat plants with Bacillus sp. V2026 increased the levels of endogenous IAA and GA in wheat of all genotypes and the level of trans-Zeatin in Sonora 64 and Leningradskaya rannyaya cvs but decreased it in AFI177 and AFI91 ultra-early lines. Interactions between the factors “genotype” and “inoculation” were significant for IAA, GA, and trans-Zeatin concentrations in wheat shoots and roots. The inoculation increased the levels of chlorophylls and carotenoids and reduced lipid peroxidation in leaves of all genotypes. The inoculation resulted in a significant increase in grain yield (by 33–62%), a reduction in the time for passing the stages of ontogenesis (by 2–3 days), and an increase in the content of macro- and microelements and protein in the grain. Early-maturing wheat genotypes showed a different response to inoculation with the bacterium Bacillus sp. V2026. Cv. Leningradskaya rannyaya was most responsive to inoculation with Bacillus sp. V2026.

Influence of environmental factors on vegetative reproduction of Lilium

Abstract. To study the effect of the spectral composition of light on the processes of plant life, the most successful source of illumination is light-emitting diodes, which allow you to receive light waves of a certain length. Currently, great prospects are associated with the development of microbial biological products based on endophytic strains of bacteria of the genus Bacillus, which inhabit internal tissues without harm to the host. The article presents the results of studies of the influence of red, blue, red + blue and white light spectra in combination with endophytic strains of B. subtilis 10–4 bacteria on the vegetative reproduction of Lilium × hybrida ‘Trendy Savannah’ in a closed room without access to sunlight. The purpose of the work is to identify the optimal conditions for obtaining high-quality planting material for lilium. Methods. The light was provided by LED modules. The bulbs of Lilium for experimental variants were soaked in B. subtilis 10–4 before planting. Scientific novelty. For the first time, specificity was revealed in the formation of vegetative and generative organs of the cultivar, as well as in the cycle of seasonal development, depending on lighting options. Results. According to the results of the conducted studies, it was revealed that to obtain bulblets, as a material for vegetative reproduction of Lilium × hybrida ‘Trendy Savannah’ in a closed room, it is most promising to use the red light spectrum without treating bulbs with bacteria; to obtain baby onions – the blue range in combination with strains of B. subtilis 10–4 bacteria. The results of two-factor dispersion analysis showed that the greatest influence of the light mode factor was revealed for the height of bulblets and the number of bulblets and the processing factor of B. subtilis bulbs 10–4 – for the diameter of bulblets and the length of the leaves of bulblets. A significant maximum of the total contribution of both factors (A × B) was noted for the width of the leaves of bulblets and the number of baby onions.

Bacteria isolated from Triticum monococcum ssp. monococcum roots can improve wheat hologenome in agriculture

BACKGROUND

Triticum monococcum ssp. monococcum is an ancestral wheat species originated from Karacadağ Mountain of Turkey more than ten thousand years ago. Because of environmental and anthropogenic effects, food supply and demand are not balanced. Agricultural activities such as breeding, and fertilization are important to sustain the balance. Conventional breeding and fertilization applications usually neglect contribution of plant related hologenomes in agricultural yield. The disruption of plant growth promoting microorganisms results in intensive usage of chemical fertilizers. The harmony between plant and plant-associated microorganisms is important for sustainability. In this study, isolation, biochemical characterization, and impact on plant growth parameters of natural bacteria associated with Triticum monococcum ssp. monococcum hologenome were aimed.

METHODS AND RESULTS

The collection of root samples and isolations of the root-associated bacterial species were carried out from local wheat lands. According to interpretation of three identification methods (MALDI-TOF, 16S rDNA, 16S-23S rDNA) eight isolates are Arthrobacter spp. ESU164, Arthrobacter spp. ESU193, Pseudomonas spp. ESU131, Pseudomonas spp. ESU141, Pseudomonas poae strain ESU182, Pseudomonas thivervalensis strain ESU192, Pseudomonas spp. ESU1531, Bacillus subtilis strain ESU181. For each isolate we investigated biochemical properties especially nitrogen fixation, phosphate solubilization, and indole-3-acetic acid production abilities. The results show that all isolates are nitrogen fixers and the best phosphate solubilizer have been reported as Pseudomonas spp. ESU131 with 2.805 ± 0.439.

CONCLUSIONS

All isolates are indole-3-acetic acid productors. 2 isolates affected the coleoptile lengths, 7 bacterial isolates showed statistically positive effect on root number, and 5 isolates promote the root lengths and the root fresh weights.