Anti-TMV Activity of Malformin A1, a Cyclic Penta-Peptide Produced by an Endophytic Fungus Aspergillus tubingensis FJBJ11

Plant-associated microorganisms are known to produce a variety of metabolites with novel structures and interesting biological activities. An endophytic fungus FJBJ11, isolated from the plant tissue of Brucea javanica (L.) Merr. (Simaroubaceae), was proven to be significantly effective in producing metabolites with anti-Tobacco mosaic virus (TMV) activities. The isolate was identified as Aspergillus tubingensis FJBJ11 based on morphological characteristics and ITS sequence. Bioassay-guided isolation led to the identification of a cycli penta-peptide, malformin A1, along with two cyclic dipeptides, cyclo (Gly-L-Pro) and cyclo (Ala-Leu). Malformin A1 showed potent inhibitory effect against the infection and replication of TMV with IC50 values of 19.7 and 45.4 μg·mL⁻¹, as tested using local lesion assay and leaf-disc method, respectively. The results indicated the potential use of malformin A1 as a leading compound or a promising candidate of new viricide.