Nematicidal activity of verrucarin A and roridin A isolated from Myrothecium verrucaria against Meloidogyne incognita

The widespread use of synthetic nematicides has caused significant problems to the environment as well as human health. To address this issue, eco-friendly control measures, such as microbial nematicides, are being developed. During the screening of Myrothecium strains with nematicidal activity against the root-knot nematode (RKN) Meloidogyne incognita, we found that the acetone extract of Myrothecium sp. KACC 40321 was highly effective against hatched juveniles of M. incognita at 7 days after exposure. The fungus was identified as Meloidogyne verrucaria. Two macrocyclic trichothecenes verrucarin A and roridin A were isolated and identified as major active metabolites by bioassay-guided fractionation and instrumental analysis. When the second-stage juveniles were treated with the chemicals, no juvenile mortality was observed. However, they effectively killed juveniles from treated eggs. The hatched juvenile mortality was used to evaluate the in vitro nematicidal activity of the compounds against M. incognita. The median effective concentrations were 1.88 μg/mL for verrucarin A and 1.50 μg/mL for roridin A. Among various liquid media, commercial malt extract broth (cMEB) was found to be the best for the production of verrucarin A and roridin A, followed by potato dextrose broth. The cMEB culture filtrate effectively reduced the formation of galls and egg masses on tomato roots in a pot experiment. In addition, the culture filtrate reduced the formation of galls on the roots of melon plants and the number of RKNs in the soils under field conditions. These results suggest that M. verrucaria KACC 40321 can be used as a biocontrol agent against RKNs in various crops. To the best of our knowledge, this is the first study to report the effectiveness of verrucarin A and rorridin A against hatched juveniles of M. incognita.