Ameliorating the drought stress tolerance of a susceptible soybean cultivar, MAUS 2 through dual inoculation with selected rhizobia and AM fungus

Design of Microbial Consortia Based on Arbuscular Mycorrhizal Fungi, Yeasts, and Bacteria to Improve the Biochemical, Nutritional, and Physiological Status of Strawberry Plants Growing under Water Deficits

Drought affects several plant physiological characteristics such as photosynthesis, carbon metabolism, and chlorophyll content, causing hormonal and nutritional imbalances and reducing nutrient uptake and transport, which inhibit growth and development. The use of bioinoculants based on plant growth-promoting microorganisms such as plant growth-promoting rhizobacteria (PGPR), yeasts, and arbuscular mycorrhizal fungi (AMF) has been proposed as an alternative to help plants tolerate drought. However, most studies have been based on the use of a single type of microorganism, while consortia studies have been scarcely performed. Therefore, the aim of this study was to evaluate different combinations of three PGPR, three AMF, and three yeasts with plant growth-promoting attributes to improve the biochemical, nutritional, and physiological behavior of strawberry plants growing under severe drought. The results showed that the growth and physiological attributes of the non-inoculated plants were significantly reduced by drought. In contrast, plants inoculated with the association of the fungus Claroideoglomus claroideum, the yeast Naganishia albida, and the rhizobacterium Burkholderia caledonica showed a stronger improvement in tolerance to drought. High biomass, relative water content, fruit number, photosynthetic rate, transpiration, stomatal conductance, quantum yield of photosystem II, N concentration, P concentration, K concentration, antioxidant activities, and chlorophyll contents were significantly improved in inoculated plants by up to 16.6%, 12.4%, 81.2%, 80%, 79.4%, 71.0%, 17.8%, 8.3%, 6.6%, 57.3%, 41%, and 22.5%, respectively, compared to stressed non-inoculated plants. Moreover, decreased malondialdehyde levels by up to 32% were registered. Our results demonstrate the feasibility of maximizing the effects of inoculation with beneficial rhizosphere microorganisms based on the prospect of more efficient combinations among different microbial groups, which is of interest to develop bioinoculants oriented to increase the growth of specific plant species in a global scenario of increasing drought stress.

Drought-Tolerant Bacteria and Arbuscular Mycorrhizal Fungi Mitigate the Detrimental Effects of Drought Stress Induced by Withholding Irrigation at Critical Growth Stages of Soybean (Glycine max, L.)

Considering current global climate change, drought stress is regarded as a major problem negatively impacting the growth of soybeans, particularly at the critical stages R3 (early pod) and R5 (seed development). Microbial inoculation is regarded as an ecologically friendly and low-cost-effective strategy for helping soybean plants withstand drought stress. The present study aimed to isolate newly drought-tolerant bacteria from native soil and evaluated their potential for producing growth-promoting substances as well as understanding how these isolated bacteria along with arbuscular mycorrhizal fungi (AMF) could mitigate drought stress in soybean plants at critical growth stages in a field experiment. In this study, 30 Bradyrhizobium isolates and 30 rhizobacterial isolates were isolated from the soybean nodules and rhizosphere, respectively. Polyethylene glycol (PEG) 6000 was used for evaluating their tolerance to drought, and then the production of growth promotion substances was evaluated under both without/with PEG. The most effective isolates (DTB4 and DTR30) were identified genetically using 16S rRNA gene. A field experiment was conducted to study the impact of inoculation with DTB4 and DTR30 along with AMF (Glomus clarum, Funneliformis mosseae, and Gigaspora margarita) on the growth and yield of drought-stressed soybeans. Our results showed that the bioinoculant applications improved the growth traits (shoot length, root length, leaf area, and dry weight), chlorophyll content, nutrient content (N, P, and K), nodulation, and yield components (pods number, seeds weight, and grain yield) of soybean plants under drought stress (p ≤ 0.05). Moreover, proline contents were decreased due to the bioinoculant applications under drought when compared to uninoculated treatments. As well as the count of bacteria, mycorrhizal colonization indices, and the activity of soil enzymes (dehydrogenase and phosphatase) were enhanced in the soybean rhizosphere under drought stress. This study's findings imply that using a mixture of bioinoculants may help soybean plants withstand drought stress, particularly during critical growth stages, and that soybean growth, productivity, and soil microbial activity were improved under drought stress.

Epigenetic regulation influenced by soil microbiota and nutrients: Paving road to epigenome editing in plants

Soil is a complex ecosystem that houses microbes and nutrients that are necessary for plant development. Edaphic properties of the soil and environmental conditions influence microbial growth and nutrient accessibility. Various environmental stimuli largely affect the soil microbes and ionic balance, in turn influencing plants. Soil microflora helps decompose organic matter and is involved in mineral uptake. The combination of soil microbes and mineral nutrients notably affects plant growth. Recent advancements have enabled a deeper understanding of plant genetic/molecular regulators. Deficiencies/sufficiencies of soil minerals and microbes also alter plant gene regulation. Gene regulation mediated by epigenetic mechanisms comprises conformational alterations in chromatin structure, DNA/histone modifications, or involvement of small RNAs. Epigenetic regulation is unique due to its potential to inherit without involving alteration of the DNA sequence. Thus, the compilation study of heritable epigenetic changes driven by nutrient imbalances and soil microbes would facilitate understanding this molecular phenomenon in plants. This information can aid in epigenome editing, which has recently emerged as a promising technology for plant non-transgenic/non-mutagenic modification. Potential epigenetic marks induced by biotic and abiotic stresses in plants could be explored as target sites for epigenome editing. This review discusses novel ways of epigenome editing to create epigenome edited plants with desirable and heritable phenotypes. As plants are sessile and in constant exposure to the soil microbiome and nutrients, epigenetic changes induced by these factors could provide more effective, stable and a sustainable molecular solution for crop improvement.