article · Frontiers in Microbiology
Rhizobacteria isolated from the tomato rhizosphere offer potential dual benefits as biofertilisers and biopesticides. Six bacterial isolates, comprising five Pseudomonas strains and one Bacillus strain, were selected for their ability to solubilise tricalcium phosphate through organic acid production. Coating tomato seeds with these isolates enhanced seed germination and established effective root colonisation in axenic soil. In greenhouse trials combining the bacteria with natural rock phosphate, inoculated plants showed substantial improvements in root and shoot growth, alongside increased levels of phosphorus, calcium, sodium, proteins, sugars, and chlorophylls after sixty days. Furthermore, two specific Pseudomonas isolates triggered induced systemic resistance against Clavibacter michiganensis subsp. michiganensis, the bacterium responsible for tomato bacterial canker, achieving a seventy-five percent plant protection rate associated with heightened defence enzymes and phenolic compounds.
Tomato crops often require substantial synthetic fertilisers and chemical pesticides to maintain yield and combat destructive pathogens such as bacterial canker. Demonstrating that naturally occurring root bacteria can both unlock soil phosphorus from natural rock phosphate and boost plant defences presents an environmentally sustainable path towards reducing chemical inputs while safeguarding crop yields.
This research provides applied greenhouse evidence for developing combined biofertiliser and biopesticide products targeted at tomato growers and commercial nurseries. The approach could enable manufacturers of biological inputs to formulate microbial seed treatments or soil inoculants using local rock phosphate. The technology currently sits at an applied testing stage, requiring field-scale validation under varied soil types and commercial growing regimes before direct market release.
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Nowadays, sustainable agriculture approaches are based on the use of biofertilizers and biopesticides. Tomato (<i>Solanum lycopersicum</i> L.) rhizosphere could provide rhizobacteria with biofertilizing and biopesticide properties. In this study, bacteria from the rhizosphere of tomato were evaluated <i>in vitro</i> for plant growth promotion (PGP) properties. Five <i>Pseudomonas</i> isolates (PsT-04c, PsT-94s, PsT-116, PsT-124, and PsT-130) and one <i>Bacillus</i> isolate (BaT-68s), with the highest ability to solubilize tricalcium phosphate (TCP) were selected for further molecular identification and characterization. Isolates showed phosphate solubilization up to 195.42 μg mL<sup>-1</sup>. All isolates showed phosphate solubilization by organic acid production. The six isolates improved seed germination and showed effective root colonization when tomato seeds were coated with isolates at 10<sup>6</sup> cfu g<sup>-1</sup> in axenic soil conditions. Furthermore, the selected isolates were tested for beneficial effects on tomato growth and nutrient status in greenhouse experiments with natural rock phosphate (RP). The results showed that inoculated tomato plants in the presence of RP have a higher shoot and root lengths and weights compared with the control. After 60 days, significant increases in plant Ca, Na, P, protein, and sugar contents were also observed in inoculated seedlings. In addition, inoculated tomato seedlings showed an increase in foliar chlorophyll a and b and total chlorophyll, while no significant changes were observed in chlorophyll fluorescence. In greenhouse, two <i>Pseudomonas</i> isolates, PsT-04c and PsT-130, showed ability to trigger induced systemic resistance in inoculated tomato seedlings when subsequently challenged by <i>Clavibacter michiganensis</i> subsp. <i>michiganensis</i>, the causal agent of tomato bacterial canker. High protection rate (75%) was concomitant to an increase in the resistance indicators: total soluble phenolic compounds, phenylalanine-ammonia lyase, and H<sub>2</sub>O<sub>2</sub>. The results strongly demonstrated the effectiveness of phosphate-solubilizing bacteria adapted to rhizosphere as biofertilizers for tomato crops and biopesticides by inducing systemic resistance to the causal agent of tomato bacterial canker disease.
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DOI: 10.3389/fmicb.2024.1289466
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