AimsThis study sought to utilize indigenous soil micro‐organisms to suppress wilt‐causing fungal pathogens of the banana.Methods and ResultsFungal pathogens were isolated from wilt‐affected rhizospheric soil, and potential antagonistic bacterial strains were isolated from healthy rhizospheric soil in the same area from which fungal pathogens were isolated. The antifungal activity of isolated micro‐organisms against fungal pathogens was studied both in vitro and in vivo against fungal pathogens. It was found that Fusarium oxysporum and Alternaria sp. were pathogenic, while Penicillium sp., Bacillus velezensis and Bacillus subtilis were antagonistic. Moreover, it was seen that B. velezensis, B. subtilis and Penicillium sp. inhibited the growth of the two fungal pathogens in both in vitro and in vivo experiments. Further investigation indicated that B. velezensis, B. subtilis and Penicillium sp. were able to produce enzymatic antifungal compounds (chitinase and β‐1,3‐glucanase). The spray application around rhizome revealed that a combination of Bacillus spp. and Penicillium sp. in greenhouse conditions gave the highest reduction in disease severity by up to 60% to both fungal pathogens among the treatments.ConclusionsBanana disease is seen to be induced not only by F. oxysporum but also by Alternaria sp. The isolated indigenous micro‐organisms can effectively control both the pathogens. The combination of isolated antagonistic micro‐organisms has thus demonstrated substantial potential for suppressing banana disease.Significance and Impact of the StudyAn antagonistic consortium isolated in this study has demonstrated remarkable potential for controlling fungal diseases caused by Fusarium sp. and Alternaria sp. Therefore, the use of indigenous microflora to improve disease suppression of banana plants against soil‐borne pathogens is a preferable approach.
He Wang,Yanjing Guo,Qing Liu,Jing Zhang,Qianlong Zhang,Mingying Yang,Qizhen Chen,Sheng Qiang,Bernal E. Valverde,Shiguo Chen
The tetramic acid moiety is a pivotal structural unit in numerous natural products. As an analogue of the simplest tetramic acid compound tenuazonic acid (TeA), sec-pentyl-TeA (S-TeA) exhibits double herbicidal activity of TeA. Here, this work identifies S-TeA as a novel natural product synthesized by Alternaria alternata and three other filamentous fungi. Chiral analysis confirm the absolute configuration of natural S-TeA as (5 S , 6 S ). Configuration-bioactivity studies reveal that natural (5 S , 6 S )-S-TeA is the eutomer and possesses the highest herbicidal activity among all tested diastereomers. Biosynthetic analyses demonstrate that threonine is the precursor to S-TeA, beginning with the production of 2-amino-3-methylhexanoic acid (AMHA) via eight enzymes from the branched-chain amino acid (BCAA) biosynthetic pathway, including threonine deaminase, 2-isopropylmalate synthase (IPMS), 3-isopropylmalate dehydratase (IPMDH), isopropylmalate dehydrogenase (ISMD), acetolactate synthase, ketol-acid reductoisomerase, dihydroxy acid dehydratase, and BCAA aminotransferase. Subsequently, AMHA undergoes acetylation and cyclization by non-ribosomal peptide synthetases to form S-TeA. Distinct differences in the biosynthetic pathways of S-TeA and TeA are identified. In vitro studies confirm the critical roles of three unique enzymes IPMS, IPMDH, and ISMD in S-TeA biosynthesis, which are absent in TeA biosynthesis. These findings provide a solid basis for developing S-TeA as a natural product herbicide.
Fluopyram is a highly effective agricultural fungicide targeting succinate dehydrogenase (SDH). Twenty-six novel amide derivatives containing azetidine were designed and synthesized with fluopyram as the lead, and their biological activities were tested. The results showed that some compounds had obvious antifungal activities against Phomopsis sp., among them, the EC 50 value of compound C24 was 5.7 mg/L, which was significantly better than fluopyram (105.4 mg/L). The curative and protective activities of compound C24 on kiwi fruit infected with Phomopsis sp. were 42.2 and 52.9 %, which were better than that of fluopyram (30.4 and 35.6 %) at 200 mg/L. Moreover, compound C24 exhibited excellent inhibitory against SDH. The results of scanning electron microscopy (SEM) indicated that the mycelium of Phomopsis sp. collapsed or even ruptured after compound C24 treatment. Meanwhile, molecular docking showed that compound C24 was deeply embedded into the SDH binding pocket, and the binding model was stabilized by a cation–π interaction with Cys-40, Tyr-58 and an H-bond with Lys-455 and Asn-452. Compound C24 can provide a valuable idea to find new succinate dehydrogenase inhibitors.
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