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Tobacco black shank (TBS), caused by Phytophthora nicotianae, is one of the most harmful diseases of tobacco. There are many studies have examined the mechanism underlying the induction of disease resistance by arbuscular mycorrhizal fungi (AMF) and β-aminobutyric acid (BABA) alone, but the synergistic effects of AMF and BABA on disease resistance have not yet been studied. This study examined the synergistic effects of BABA application and AMF inoculation on the immune response to TBS in tobacco. The results showed that spraying BABA on leaves could increase the colonization rate of AMF, the disease index of tobacco infected by P.nicotianae treated with AMF and BABA was lower than that of P.nicotianae alone. The control effect of AMF and BABA on tobacco infected by P.nicotianae was higher than that of AMF or BABA and P.nicotianae alone. Joint application of AMF and BABA significantly increased the content of N, P, and K in the leaves and roots, in the joint AMF and BABA treatment than in the sole P. nicotianae treatment. The dry weight of plants treated with AMF and BABA was 22.3% higher than that treated with P.nicotianae alone. In comparison to P. nicotianae alone, the combination treatment with AMF and BABA had increased Pn, Gs, Tr, and root activity, while P. nicotianae alone had reduced Ci, H2O2 content, and MDA levels. SOD, POD, CAT, APX, and Ph activity and expression levels were increased under the combined treatment of AMF and BABA than in P.nicotianae alone. In comparison to the treatment of P.nicotianae alone, the combined use of AMF and BABA increased the accumulation of GSH, proline, total phenols, and flavonoids. Therefore, the joint application of AMF and BABA can enhance the TBS resistance of tobacco plants to a greater degree than the application of either AMF or BABA alone. In summary, the application of defense-related amino acids, combined with inoculation with AMF, significantly promoted immune responses in tobacco. Our findings provide new insights that will aid the development and use of green disease control agents.

Pairs polyphylla var. yunnanensis is a perennial herb, and its rhizomes are used as medicine to invigorate blood circulation, dissipate blood stasis, relieve swelling and pain, clear heat and detoxify the body. However, due to its slow growth, most of the saponin content is low, while the content of saponins is higher in Paris fargesii Franch of the same genus. The isolation and screening of strains from P. fargesii Franch that promote the accumulation of saponin content in P. polyphylla var. yunnanensis is important to improve the growth rate of artificially cultivated P. polyphylla var. yunnanensis and increase its medicinal activity. Plant symbiotic strains are biologically active microorganisms that can promote the growth and development of host plants through direct probiotic effects and indirect disease resistance mechanisms. Here, we isolated four strains of symbiotes, including two bacteria, Bacillus cereus (LgD2) and Bacillus thuringiensis (LgD10), and two fungi, Aspergillus tamari (TPD11) and Fusarium oxysporum (TPB). All of them promoted the biomass, chlorophyll content and photosynthetic efficiency of P. polyphylla var. yunnanensis seedlings to different degrees and effectively stimulated the accumulation of saponin content in P. polyphylla var. yunnanensis seedlings to improve the expression of saponin synthesis pathway genes. The symbiotes also promoted the enzymatic activities of the enzymes superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine aminolase (PAL), improved the physiological indicators of tobacco plants (plant height, crown width, leaf length and leaf width), reduced the incidence of tobacco black shank, and improved the growth and resistance-related genes of tobacco. In conclusion, the four symbiotic strains TPD11, TPB, LgD10 and LgD2 play an important role in regulating the growth, promoting saponin accumulation, and disease resistance of P. polyphylla var. yunnanensis.

Tobacco black shank (TBS), caused by Phytophthora nicotianae, is one of the most harmful diseases of tobacco. There are many studies have examined the mechanism underlying the induction of disease resistance by arbuscular mycorrhizal fungi (AMF) and Ɓ-aminobutyric acid (BABA) alone, but the synergistic effects of AMF and BABA on disease resistance have not yet been studied. This study examined the synergistic effects of BABA application and AMF inoculation on the immune response to TBS in tobacco. The results showed that spraying BABA on leaves could increase the colonization rate of AMF, the disease index of tobacco infected by P.nicotianae treated with AMF and BABA was lower than that of P.nicotianae alone. The control effect of AMF and BABA on tobacco infected by P.nicotianae was higher than that of AMF or BABA and P.nicotianae alone. Joint application of AMF and BABA significantly increased the content of N, P, and K in the leaves and roots, in the joint AMF and BABA treatment than in the sole P. nicotianae treatment. The dry weight of plants treated with AMF and BABA was 22.3% higher than that treated with P.nicotianae alone. In comparison to P. nicotianae alone, the combination treatment with AMF and BABA had increased Pn, Gs, Tr, and root activity, while P. nicotianae alone had reduced Ci, H2O2 content, and MDA levels. SOD, POD, CAT, APX, and Ph activity and expression levels were increased under the combined treatment of AMF and BABA than in P.nicotianae alone. In comparison to the treatment of P.nicotianae alone, the combined use of AMF and BABA increased the accumulation of GSH, proline, total phenols, and flavonoids. Therefore, the joint application of AMF and BABA can enhance the TBS resistance of tobacco plants to a greater degree than the application of either AMF or BABA alone. In summary, the application of defense-related amino acids, combined with inoculation with AMF, significantly promoted immune responses in tobacco. Our findings provide new insights that will aid the development and use of green disease control agents. [ABSTRACT FROM AUTHOR]