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

Abstract

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.

Keywords: antioxidant activity; arbuscular mycorrhizal fungi; drought stress; microbial consortia; plant growth-promoting microorganisms; strawberry.

Figure 1

Mycorrhizal colonization frequency (MCF) (A) and mycorrhization intensity (MI) (B) in strawberry plants inoculated with microbial consortia under water deficit (30% of WHC). The colonization was not registered in the uninoculated controls; therefore, it was excluded from the figure. Cc: Claroideoglomus claroideum; Cl: Claroideoglomus lamellosum; Fm: Funneliformis mosseae; Cg: Candida guillermondii; Na: Naganishia albida; Rm: Rhodotorula mucilaginosa; Pf: Pseudomonas frederiksbergensis; Bt: Bacillus tequilensis; Bc: Burkholderia caledonica. Values represent means ± SE. Different letters indicate significant differences using LSD test (p ≤ 0.05).

Figure 2

Photosynthetic behavior in strawberry plants inoculated with microbial consortia under water deficit. WW: well-watered (irrigated up to 85% of WHC); WS: water-stressed (irrigated up to 30% of WHC). (A) stomatal conductance (gs); (B) photosynthesis (A); (C) transpiration (E); (D) photosystem II (ΦPSII). Cc: Claroideoglomus claroideum; Cl: Claroideoglomus lamellosum; Fm: Funneliformis mosseae; Cg: Candida guillermondii; Na: Naganishia albida; Rm: Rhodotorula mucilaginosa; Pf: Pseudomonas frederiksbergensis; Bt: Bacillus tequilensis; Bc: Burkholderia caledonica. Values represent means ± SE. Different letters indicate significant differences using LSD test (p ≤ 0.05).

Figure 3

k-means clustering algorithm ordination, clustering similar variables based on an unsupervised machine learning method. WW: well-watered; WS: water-stressed; CS1: Fm+Rm+Pf; CS2: Fm+Rm+Bt; CS3: Fm+Rm+Bc; CS4: Fm+Cg+Pf; CS5: Fm+Cg+Bt; CS6: Fm+Cg+Bc; CS7: Fm+Na+Pf; CS8: Fm+Na+Bt; CS9: Fm+Na+Bc; CS10: Cl+Rm+Pf; CS11: Cl+Rm+Bt; CS12: Cl+Rm+Bc; CS13: Cl+Cg+Pf; CS14: Cl+Cg+Bt; CS15: Cl+Cg+Bc; CS16: Cl+Na+Pf; CS17: Cl+Na+Bt; CS18: Cl+Na+Bc; CS19: Cc+Rm+Pf; CS20: Cc+Rm+Bt; CS21: Cc+Rm+Bc; CS22: Cc+Cg+Pf; CS23: Cc+Cg+Bt; CS24: Cc+Cg+Bc; CS25: Cc+Na+Pf; CS26: Cc+Na+Bt; CS27: Cc+Na+Bc.

Figure 4

Phenolic compounds and antioxidant activities of leaves of strawberry plants under water stress and inoculated with microbial consortia. (A) Total phenols determined by the Folin–Ciocalteu method; (B) antioxidant activity (AA) determined by the TEAC (Trolox equivalent antioxidant capacity) method; (C) CUPRAC (copper reducing antioxidant capacity) method; (D) DPPH (2,2-diphenyl-1-picrylhydrazyl) method. WW: well-watered (irrigated up to 85% WHC); WS: water-stressed (irrigated up to 30% of WHC). Cc: Claroideoglomus claroideum; Fm: Funneliformis mosseae; Cg: Candida guillermondii; Na: Naganishia albida; Rm: Rhodotorula mucilaginosa; Pf: Pseudomonas frederiksbergensis; Bt: Bacillus tequilensis; Bc: Burkholderia caledonica. Values represent means ± SE. Different letters indicate significant differences using LSD test (p ≤ 0.05).

Figure 5

Malondialdehyde (MDA) content in strawberry plant shoots inoculated with microbial consortia under water deficit (irrigated to 30% WHC). WW: well-watered (irrigated up to 85% WHC); WS: water-stressed (irrigated up to 30% of WHC); Cc: C. claroideum; Fm: F. mossea; Cg: C. guillermondii; Na: N. albida; Rm: R. mucilaginosa; Pf: P. frederiksbergensis; Bt: B. tequilensis; Bc: B. caledonica. Values represent means ± SE. Different letters indicate significant differences using LSD test (p ≤ 0.05).

Figure 6

Principal component analysis (PCA) biplot in strawberry plant shoots inoculated with microbial consortia under water deficit (irrigated to 30% substrate) based on biomass production of shoots and root (SDW and RDW); relative water content (RWC); root–shoot relation; mycorrhizal colonization frequency (%MCF); mycorrhization intensity (%MI); net photosynthesis (A); transpiration (E); stomatal conductance (gs); chlorophyll a (Chl a); chlorophyll b (Chl b); total chlorophyll (Total Chl), carotenoids (CARs); total phenolic compounds (TP); antioxidant activities determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH), Trolox equivalent antioxidant capacity (TEAC), and copper reducing antioxidant capacity (CUPRAC) methods; malondialdehyde (MDA) content; and nitrogen (N), phosphorus (P), and potassium (K) concentrations in the shoot. WS: well-watered (irrigated up to 85% WHC); WS: water-stressed (irrigated up to 30% of WHC).