Plant organ- and growth stage-diversity of endophytic bacteria with potential as biofertilisers isolated from wheat (Triticum aestivum L.)

Screening of Endophytic Antagonistic Bacteria in Wheat and Evaluation of Biocontrol Potential against Wheat Stripe Rust

Wheat stripe rust is globally one of the most important diseases affecting wheat. There is an urgent need to develop environmentally safe and durable biological control options to supplement the control that is achieved with breeding and fungicides. In this study, endophytic bacteria were isolated from healthy wheat through the tissue separation method. Antagonistic endophytic bacteria were screened based on the control effect of urediniospore germination and wheat stripe rust (WSR). The taxonomic status of antagonistic strains was determined based on morphological, physiological, and biochemical characteristics and molecular biological identification (16S rDNA and gyrB gene sequence analysis). Finally, the potential growth-promoting effect of different concentrations of antagonists on wheat seedlings and the biological control effect of WSR were studied. A total of 136 strains of endophytic bacteria belonging to 38 genera were isolated. Pseudomonas was the most common bacterial genus, with 29 isolates (21%). The biological control effect of different isolates was assessed using an urediniospore germination assay. The isolate XD29-G1 of Paenibacillus polymyxa had the best performance, with 85% inhibition of spore germination during primary screening. In the deep screening, the control effect of XD29-G1 on wheat stripe rust was 60%. The antagonist XD29-G1 promoted the germination of wheat seeds and the growth of wheat seedlings at a solution dilution of 10-7 cfu/mL. The pot experiment results showed that different dilution concentrations of the strain had different levels of antibacterial activity against WSR, with the concentration of 10-1 cfu/mL having the best control effect and a control efficiency of 61.19%. XD29-G1 has better biological control potential against wheat stripe rust.

Diversity and correlation analysis of endophytes and metabolites of Panax quinquefolius L. in various tissues

BACKGROUND

Panax quinquefolius L. (American ginseng) is widely used in medicine due to its wealth of diverse pharmacological effects. Endophytes colonize within P. quinquefolius in multiple tissue types. However, the relationship between endophytes and the production of their active ingredients in different parts of the plant is not clear.

RESULTS

In this study, the relationship of endophytic diversity and the metabolites produced in different plant tissues of P. quinquefolius were analyzed using metagenomic and metabolomic approaches. The results showed relatively similar endophyte composition in roots and fibrils, but obvious differences between endophyte populations in stems and leaves. Species abundance analysis showed that at the phylum level, the dominant bacterial phylum was Cyanobacteria for roots, fibrils, stems and leaves, Ascomycota forroots and fibrils roots, and Basidiomycota for stems and leaves. LC-MS/MS technology was used to quantitatively analyze the metabolites in different tissues of P. quinquefolius. A total of 398 metabolites and 294 differential metaboliteswere identified, mainly organic acids, sugars, amino acids, polyphenols, and saponins. Most of the differential metabolites were enriched in metabolic pathways such as phenylpropane biosynthesis, flavonoid biosynthesis, citric acid cycle, and amino acid biosynthesis. Correlation analysis showed a positive and negative correlation between the endophytes and the differential metabolites. Conexibacter significantly enriched in root and fibril was significantly positively correlated with saponin differential metabolites, while cyberlindnera significantly enriched in stem and leaf was significantly negatively correlated with differential metabolites (p < 0.05).

CONCLUSION

The endophytic communities diversity were relatively similar in the roots and fibrils of P. quinquefolius, while there were greater differences between the stems and leaves. There was significant difference in metabolite content between different tissues of P. quinquefolius. Correlation analysis methods demonstrated a correlation between endophytes and differential metabolism.

Seed dressing with M451 promotes seedling growth in wheat and reduces root phytopathogenic fungi without affecting endophytes

Fungal plant infections result in substantial losses to the agricultural sector. A range of fungicide seed dressings are available to control seed-borne fungal diseases; however, they lack sufficient efficacy because of intrinsic tolerance and acquired resistance. Moreover, many fungicide seed dressings can also penetrate plants, negatively affecting plant growth owing to their toxic effects on endophytes, as well as contributing to the spread of antibiotic resistance. Here, we evaluated the efficacy of M451, a member of a new class of antimicrobial agents that are not relevant to human healthcare. As a seed dressing for wheat seeds, M451 exhibited significant antifungal activity against one of the most devastating plant fungal pathogens, Fusarium spp. Furthermore, M451 was more active than the commercially used fungicide Maxim XL against both seed-borne and soil-borne F. oxysporum infection. Importantly, and unlike other antifungals, M451 seed dressing did not inhibit any of the major characteristics of wheat grains and seedlings, such as germination percentage, germination time, grain vigor, shoot- and root weight and length, but rather improved some of these parameters. The results also demonstrated that M451 had no negative impacts on endophytes and did not accumulate in grains. Thus, M451 may have potential applications as an antifungal agent in wheat cultivation.

Culturable bacterial endophytes of Aconitum carmichaelii Debx. were diverse in phylogeny, plant growth promotion, and antifungal potential

Medicinal plants harbor tremendously diverse bacterial endophytes that maintain plant growth and health. In the present study, a total of 124 culturable bacterial endophytes were isolated from healthy Aconitum carmichaelii Debx. plants. These strains were clustered into 10 genera based on full-length 16S rDNA sequences, among which Bacillus and Pseudomonas were the dominant genera. In addition, A. carmichaelii may capture 10 potential new bacterial species based on multi-locus sequence analysis of three housekeeping genes (gyrA, rpoB, and atpD). The majority of these bacterial endophytes exhibited plant growth-promoting ability through diverse actions including the production of either indole acetic acid and siderophore or hydrolytic enzymes (glucanase, cellulose, and protease) and solubilization of phosphate or potassium. A total of 20 strains inhibited hyphal growth of fungal pathogens Sclerotium rolfsii and Fusarium oxysporum in vitro on root slices of A. carmichaelii by the dual-culture method, among which Pseudomonas sp. SWUSTb-19 showed the best antagonistic activity. Field experiment confirmed that Pseudomonas sp. SWUSTb-19 significantly reduced the occurrence of southern blight and promoted plant biomass compared with non-inoculation treatment. The possible mode of actions for Pseudomonas sp. SWUSTb-19 to antagonize against S. rolfsii involved the production of glucanase, siderophore, lipopeptides, and antimicrobial volatile compounds. Altogether, this study revealed that A. carmichaelii harbored diverse plant growth-promoting bacterial endophytes, and Pseudomonas sp. SWUSTb-19 could be served as a potential biocontrol agent against southern blight.

Harnessing Native Bacillus spp. for Sustainable Wheat Production

The genus Bacillus has been widely applied in contemporary agriculture as an environmentally-friendly biological agent. However, the real effect of commercial Bacillus-based fertilizers and pesticides varies immensely in the field. To harness Bacillus for efficient wheat production, we reviewed the diversity, functionality, and applicability of wheat-associated native Bacillus for the first time. Our main findings are: (i) Bacillus spp. inhabit the rhizosphere, root, stem, leaf, and kernel of wheat; (ii) B. subtilis and B. velezensis are the most widely endophytic species that can be isolated from both below and aboveground tissues; (iii) major functions of these representative strains are promotion of plant growth and alleviation of both abiotic and biotic stresses in wheat; (iv) stability and effectiveness are 2 major challenges during field application; (v) a STVAE pipeline that includes 5 processes, namely, Screen, Test, Validation, Application, and Evaluation, has been proposed for the capture and refinement of wheat-associated Bacillus spp. In particular, this review comprehensively addresses possible solutions, concerns, and criteria during the development of native Bacillus-based inoculants for sustainable wheat production.

Diversity and Exploration of Endophytic Bacilli for the Management of Head Scab (Fusarium graminearum) of Wheat

Fusarium graminearum causing head scab (HS) or head blight (HB) disease in wheat is one of the nasty fungi reported to cause significant grain quality and yield loss. Biological control using endophytic bacteria has emerged as a prospective option for containing fungal diseases in an environmentally benevolent, durable, and sustainable manner. In this regard, 112 endophytic bacilli were isolated from the anthesis stage (Zadok’s growth stage 65) from five different wheat genotypes with an aim to identify prospective antagonistic strains against F. graminearum. The molecular identity of the strains was confirmed by matching 16S rRNA sequences of bacterial strains with the gene sequences of type strains available in the National Center for Biotechnology Information database and reported 38 different species of Bacillus in all the five wheat cultivars. Further, it has been observed that only fourteen strains (B. clarus NOK09, B. mojavensis NOK16, B. subtilis NOK33, B. rugosus NOK47, B. mojavensis NOK52, B. clarus NOK59, B. coahuilensis NOK72, B. cabrialesii NOK78, B. cabrialesii NOK82, B. rugosus NOK85, B. amyloliquefaciens NOK89, B. australimaris NOK95, B. pumilus NOK103, and B. amyloliquefaciens NOK109) displayed in-vitro antagonistic effect against Fusarium graminearum fungus. Furthermore, the three endophytic Bacillus strains showing the strongest antagonistic effect (>70% of growth inhibition of fungal mycelium) under in-vitro antagonistic assay were selected for field experiments. In a two-year consecutive field study, a combination of three strains (B. clarus NOK09 + B. subtilis NOK33 + B. amyloliquefaciens NOK109) displayed a remarkable reduction in HS disease index by 81.47% and 77.85%, respectively. Polymerase chain reaction assay detected three genes (ituD, bmyC, and srfA) involved in antibiotic biosynthesis pathways. Additional attributes such as potassium solubilization, siderophore release, and hydrolytic enzyme (protease, lipase, amylase, chitinase, and pectinase) synthesis have been observed in these strains. Overall, the present study was successful in profiling endophytic bacilli and selecting the combination of effective antagonistic endophytic Bacillus strains that could be the best alternative for the sustainable and ecological sound management of HS disease in wheat under field conditions.