Endophytic fungi and rhizobacteria: beneficial effects on plants

Abstract

The concern with sustainable agriculture without causing losses in crop yields reinvigorates scientific research with special attention focused on beneficial microorganisms. These microorganisms may cooperate with plant growth, playing essential functions in soil fertility, plant nutrition and health. The increase in the number of biological products available in the market is a worldwide reality and the exploitation of the skills of beneficial fungi, bacteria and virus has been attractive. However, to make this a reality, a lot of investigation is needed. In the first part of this work, we isolated six strains of the endophytic fungus Induratia spp. and identified through phylogenetic analysis. These Induratia strains were able to produce volatile organic compounds (VOCs) with antimicrobial activity against the following tested plant pathogens: Phytophthora sp., Rhizoctonia solani, Botrytis cinerea, Colletotrichum lindemuthianum, Sclerotinia sclerotiorum and Fusarium verticillioides. The Induratia strains produced 17 different VOCs as determined by the solid-phase microextraction followed by gas chromatography-mass spectrometry method (SPME-GCMS). Among the in vitro-tested strains, FTB has shown the best results against most pathogens and was tested in vivo for its capacity to control B. cinerea on strawberry fruits stored in hermetically closed boxes, where it was shown to increase the shelf life of the fruits. This novel Induratia strain showed potential to be further developed into a commercial product and a patent was deposited under number BR 10 2021 001666 3. In the second part of this work, we explored the microbiota in the rhizosphere of faba bean, oat, oilseed rape, wheat or bare fallow soil to isolate, functionally characterize with cultural methods, and molecularly identify the strains by sequence analysis of the16S rDNA. A total of 138 bacterial strains were obtained and their potential for phosphorus (P) solubilisation from aluminium phosphate, tricalcium phosphate, iron phosphate, phytate mineralisation, potassium (K) solubilisation, siderophore production, endogenous nitrate and Fusarium graminearum inhibition was tested in vitro. The most common plant growth promotion (PGP) activity was represented by P solubilisation from aluminium phosphate, followed by K solubilisation. Bacterial strains displaying iron phosphate phosphate solubilisation and mineral P solubilisation from phytate were found only with oilseed rape and faba bean rhizosphere. Approximately, 68% of the bacterial strains displayed two or more activities. In total 10 genera were identified: Pseudomonas, Stenotrophomonas, Comamonas, Arthrobacter, Agromyces, Rhodococcus, Streptomyces, Serratia, Lelliotia and Paenisporosarcina. The most common genera were Pseudomonas (44.2%), followed by Stenotrophomonas (23.2%). A bioassay with wheat seeds was performed with 4 strains chosen by their good performance in the in vitro functional bioassays and these strains showed significant increases in root and shoot biomasses. Therefore, several strains have shown potential as biofertilizers and biocontrol agents, constituting alternatives to chemicals in sustainable agricultural crop production.