Endophytic fungi promote seed germination

Natural bioactive substances derived from microorganisms are the key to developing new biological agents and have been widely used in agriculture, medicine, nutrition and health. The improper use of chemicals and fertilizers has caused great side effects on the agro-ecosystem, which also directly or indirectly affects people's diet and health. In addition, the long-term continuous use of chemical agents provides a directional selection pressure for diseases and insects, and in recent years, superbacteria and multi-resistant pathogenic microorganisms have been reported one after another. Therefore, the discovery and creation of new natural source biologics to meet agricultural production is particularly urgent, and this expanding demand is more important than ever. Endophytic fungi are found in most plants and colonize inside plant tissues. Some beneficial endophytes help plants absorb nutrients. They also produce chemicals that promote plant growth and antimicrobial substances that are essential for plant survival. In view of this, the researchers isolated and identified endophytic fungi from different plant species and systematically evaluated their potential for promoting seed germination.

In this study, 75 endophytic fungi with distinct morphological differences were isolated from the leaf and stem tissues of 26 different plants by tissue separation. The spore suspensions of all strains were prepared by liquid culture, and their effects on corn seed germination were verified one by one. Three endophytic fungi with significantly higher germination rate were selected. After culture and microscopic morphology observation, Combined with ITS sequence phylogenetic analysis, the three strains were identified as Alternaria alternate AUMC15170, respectively. Aspergilus flavus AUMC 15171 (Aspergillus flavus) and Aspergillus terreus AUMC 15172 (Aspergillus terreus). Further, the researchers explored the ability of 3 endophytic fungi to produce ferric support and secrete indoleacetic acid. The test results showed that compared with Aspergillus aflatus AUMC 15171 and Aspergillus terreus AUMC 15172, the IAA produced by crosslinked spora AUMC15170 was the highest, with 23.6 µg/ml. AUMC 15171 was 21.3µg /ml for Aspergillus flavus and 20.88µg /ml for Aspergillus terreus. On the medium of CAS detection, the three strains could not produce obvious hydrolytic halo, which proved that they could not produce iron carriers. The results of phosphorus solubilization test showed that all the three endophytic fungi could dissolve phosphate, and strain AUMC 15170 had the strongest phosphate solubilization ability, reaching 4.517 µg/ml. In addition, the active metabolites were extracted from different strains by chloroform fermentation solution, and the antioxidant and antifungal activities of the extracts against different plant pathogens were determined. The results showed that A. alternata AUMC15170, A. flavus AUMC1517 and A. terreus AUMC1517 had good free radical scavenging activity, and the scavenging rates of DPPH were 67.81, 58.55 and 73.49%, respectively. It also has good antibacterial activity against various plant pathogenic fungi such as botrytis cinerea and Fusarium. A variety of compounds with known functional activities and active substances that have not yet been reported were detected by gas chromatography-tandem mass spectrometry. It was proved that the antibacterial and germ-promoting activities of these three endophytic fungi may be closely related to these metabolites.

In general, the use of endophytic bacteria to promote germination has broad application prospects in seed technology and agricultural production. The development and utilization of endophytic fungal cultures and their extracts can provide a good reference for sustainable agriculture.

FIG. 1 Isolation of maize endophytic fungi and the ability of chloroform extract to promote seed germination

FIG. 2 Morphological and phylogenetic analysis of endogenous Alternaria alternata