Nematicidal activity of volatile fatty acids generated from wheat bran in reductive soil disinfestation

Abstract

We tried to elucidate the mechanisms of soil disinfestation by a combined treatment of wheat bran amendment, temporary flooding, and tarping with plastic film (reductive soil disinfestation, RSD). In a laboratory experiment, redox potential decreased to under -200 mV in RSD-treated soil and short-chain volatile fatty acids (VFAs), such as acetic and n-butyric acids, were generated at levels of 9.8 to 10.8 mM in the soil solution in 48 hr. VFAs showed high nematicidal activities when second-stage juveniles of Meloidogyne incognita were exposed to them at 10 mM for 24 hr. Acetic and n-butyric acids had nearly equal nematicidal activity and their mixtures showed an additive effect. VFAs increased the nematicidal activity with decreasing pH, indicating that nematicidal activities of VFAs are related to their ionization. Logistic LC50 of nonionized acetic acid was estimated to be 5.6 ± 0.2 (SEM) mM. In a field demonstration, RSD was confirmed to be adequate for nematode control, and 5.7 mM of acetic acid and 1.5 mM of n-butyric acid were calculated in the water-phase of the soil, although the soil pH was not low enough to form nonionized acids at the lethal concentration. These results show that VFAs generated by soil microorganisms in reduced soil probably play an important role in nematode suppression in practice.