Abstract
Plant growth-promoting microbes (PGPM) play vital roles in maintaining crop fitness and soil health in stressed environments. Research have included analysis-based cultivation of soil-microbial-plant relationships to clarify microbiota potential. The goal of the research was to (i) evaluate the symbiotic microorganism effects on tomato seedling fitness under stressed conditions simulating a fragile soil susceptible to degradation; (ii) compare the plant-microbial interactions after inoculation with microbial isolates and fungi-bacteria consortia; (iii) develop an effective crop-microbial network, which improves soil and plant status. The experimental design included non-inoculated treatments with peat and sand at ratios of 50:50, 70:30, 100:0 (v:v), inoculated treatments with arbuscular mycorrhizal fungi (AMF) and Azospirillum brasilense (AZ) using the aforementioned peat:sand ratios; and treatment with peat co-inoculated with AMF and Saccharothrix tamanrassetensis (S). AMF + AZ increased root fresh weight in peat substrate compared to the control (4.4 to 3.3 g plant-1). An increase in shoot fresh weight was detected in the AMF + AZ treatment with a 50:50 peat:sand ratio (10.1 to 8.5 g plant-1). AMF + AZ reduced antioxidant activity (DPPH) (18-34%) in leaves, whereas AMF + S had the highest DPPH in leaves and roots (45%). Total leaf phenolic content was higher in control with a decreased proportion of peat. Peroxidase activity was enhanced in AMF + AZ and AMF + S treatments, except for AMF + AZ in peat. Microscopic root assays revealed the ability of AMF to establish strong fungal-tomato symbiosis; the colonization rate was 78-89%. AMF + AZ accelerated K and Mg accumulation in tomato leaves in treatments reflecting soil stress. To date, there has been no relevant information regarding the successful AMF and Saccharothrix co-inoculation relationship. This study confirmed that AMF + S could increase the P, S, and Fe status of seedlings under high organic C content conditions. The improved tomato growth and nutrient acquisition demonstrated the potential of PGPM colonization under degraded soil conditions.
Highlights
The predicted and persistent threat of soil degradation driven by climatic and anthropogenic forces necessitates the development of strict directives for the protection of soils, as recently promoted by the European Union [1]
The phylum Actinobacteria represents a large group of non-mycorrhizal plant growth promoting microorganisms (PGPM), among them Saccharothrix spp. are aerobic, gram-positive actinomycetes with branching vegetative mycelium, that fragments into rod-shaped spores [20]
PGPM and their positive impact on the plant have not been as broadly studied as arbuscular mycorrhizal fungi (AMF), some studies have reported their beneficial effects on crops [22]
Summary
The predicted and persistent threat of soil degradation driven by climatic and anthropogenic forces necessitates the development of strict directives for the protection of soils, as recently promoted by the European Union [1]. Root-associated arbuscular mycorrhizal fungi AMF application is highly effective, resulting in the improvement of crop growth, health, yield, and general fitness [9,10,11]. PGPM and their positive impact on the plant have not been as broadly studied as AMF, some studies have reported their beneficial effects on crops [22]. The probability of shifting the “microbiological equilibrium” of the rhizosphere and controlling it to favor the growth, yield, and health of crops is much greater if consortia of beneficial and effective microorganisms are introduced that are physiologically and ecologically compatible with one another [25,26,27]. The direct effects of PGPM on the trade-off among microbes and plants are still poorly understood regarding soil and crop fitness
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