C-Alkylated flavonoids from the whole plants of Desmodium caudatum and their anti-TMV activity.

BACKGROUND: Natural products are important sources of biopesticides to control plant virus, and flavonoids are identified as promising anti-tobacco mosaic virus (TMV) agents. Since Desmodium caudatum is a rich source of flavonoids, this study focuses on the discovery of the new anti-TMV active flavonoids from D. caudatum and their possible mode of action. RESULTS: Three new (compounds 1-3) and nine known (compounds 4-12) C-alkylated flavonoids were isolated from D. caudatum. To the best of our knowledge, the framework of 1-3 was reported in natural products for the first time. In addition, 1-3, 5, and 6 showed notable anti-TMV activity with inhibition rates in the range of 35.8-64.3% at a concentration of 50 µg/mL, and these rates are higher than that of positive control (with inhibition rates of 34.6% ± 2.8). In addition, the structure-activity relationship study revealed that the (pyrrol-2-yl)methyl moiety on flavone can significantly increases the activity. This result is helpful to find new anti-TMV inhibitors. CONCLUSION: C-Alkylated flavonoids showed potent activities against TMV with multiple modes of actions. The increase of defense-related enzyme activities, up-regulate the expression of defense related genes, down-regulate the expression of Hsp70 protein by inhibiting the related Hsp genes that are involved in tobacco resistance to TMV. By the actions mentioned earlier, the infection of TMV was influenced, thereby achieving the effects of control of TMV. The successful isolation of the earlier-mentioned flavonoids provide the new source of biopesticides to TMV proliferation, and also contribute to the utilization of D. caudatum. © 2023 Society of Chemical Industry.

[Effects of Trichoderma longbrachitum and Streptomyces jingyangensis combination on the growth and disease resistance of tobacco seedlings].

An agar plate antagonism experiment in combining with in vivo screening experiment was conducted to study the affinity and bacteriostasis spectrum of the combination of biocontrol agents Trichoderma longbrachitum and Streptomyces jingyangensis to Nicotiana tabacum seedlings, with the effects of each agent and their combination on the N. tabacum seedlings growth, induced resistance, and resistance to Phytophthora nicotianae analyzed. The two agents had no interactive inhibitory effect and showed higher affinity to N. tabacum, and the agents themselves as well as their metabolites had higher bacteriostasis activities and wider bacteriostasis spectrum to P. nicotiaonae, Pythium aphanidermatum, and Alternaria alternate in different habitats. The combination of the two agents affected the morphological characteristics of the seedlings underground and aboveground parts, promoted the growth of root, stem, and leaf, and increased the root volume, total surface area, length, and average diameter as well as the stem height and size and the leaf length, width, and biomass, with these promotion effects being superior than those of the single-agent treatment. The combination of the two agents also increased the activities of the defensive enzymes superoxide dismutase, catalase, phenylalanine ammonia lyase, and peroxidase in the seedlings root significantly, with the relative control efficiency against P. nicotianae reached 69.3%, as compared to the conventional treatment. This study showed that the combination of T. longbrachitum and S. jingyangensis was a compatible combination with higher affinity and efficiency. This combination showed a synergistic effect of the two agents in plant disease control and in promoting plant growth, being able to promote the tobacco seedlings growth and control the P. nicotianae effectively.