Abstract
Among 200 fungal strains isolated from the soil, only one culture filtrate of Aspergillus flavus JCK-4087 showed strong nematicidal activity against Meloidogyne incognita. The nematicidal metabolite isolated from the culture filtrate of JCK-4087 was identified as cyclopiazonic acid (CPA). Because JCK-4087 also produced aflatoxins, six strains of Penicillium commune, which have been reported to be CPA producers, were obtained from the bank and then tested for their CPA productivity. CPA was isolated from the culture filtrate of P. commune KACC 45973. CPA killed the second-stage juveniles of M. incognita, M. hapla, and M. arearia with EC50–3 days 4.50, 18.82, and 60.51 μg mL–1, respectively. CPA also significantly inhibited egg hatch of M. incognita and M. hapla after a total of 28 days of treatment with the concentrations > 25 μg mL–1. The enhancement of CPA production by P. commune KACC 45973 was explored using an optimized medium based on Plackett–Burman design (PBD) and central composite design (CCD). The highest CPA production (381.48 μg mL–1) was obtained from the optimized medium, exhibiting an increase of 7.88 times when compared with that from potato dextrose broth culture. Application of the wettable power-type formulation of the ethyl acetate extract of the culture filtrate of KACC 45973 reduced gall formation and nematode populations in tomato roots and soils under greenhouse conditions. These results suggest that CPA produced by P. commune KACC 45973 can be used as either a biochemical nematicide or a lead molecule for developing chemical nematicides to control root-knot nematodes.
Highlights
Plant-parasitic nematodes (PPNs) are economic burdens in agriculture, owing to their direct and indirect damages that lead to crop yield losses (Bogner et al, 2017); they are estimated to cause an annual yield loss of $173 billion
The objectives of this study were (1) to isolate and identify cyclopiazonic acid (CPA) from the fermentation filtrate of A. flavus JCK-4087 and P. commune Korean Agricultural Culture Collection (KACC) 45973, (2) to investigate in vitro nematicidal activity of CPA against Root-knot nematodes (RKNs), (3) to optimize culture conditions using Plackett–Burman design (PBD) and central composite design (CCD) for CPA production by P. commune, and (4) to evaluate the disease control efficacy of ethyl acetate layer extracted from P. commune KACC 45973 against root-knot nematode disease in tomato plants
Kojic acid isolated from Aspergillus oryzae exhibited nematicidal activity against M. incognita (Kim et al, 2016), and oxalic acid produced by Aspergillus niger F22 showed 100% J2s mortality and 95% egg hatch inhibitory activity against M. incognita at 2 mmol L−1 (Jang et al, 2016)
Summary
Plant-parasitic nematodes (PPNs) are economic burdens in agriculture, owing to their direct and indirect damages that lead to crop yield losses (Bogner et al, 2017); they are estimated to cause an annual yield loss of $173 billion. Root-knot nematodes (RKNs; Meloidogyne spp.) are the most damaging PPNs to various crops (Termorshuizen et al, 2011; Kim et al, 2016; Gamalero and Glick, 2020). Among several identified RKN species, Meloidogyne arenaria, M. hapla, M. incognita, and M. javanca are commonly reported worldwide (Anwar and McKenry, 2010; Jones et al, 2013; Dong et al, 2014; Kim et al, 2018; Gamalero and Glick, 2020). Various chemical nematicides have been used to control RKNs on different crops worldwide. Numerous nematicidal metabolites from fungal biocontrol agents have been reported for the control of RKNs, including thermolides A and B, omphalotins, ophiobolins, bursaphelocides A and B, illinitone A, speudohalonectriins A and B, dichomitin B, and caryopsomycins A-C (Degenkolb and Vilcinskas, 2016)
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