Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: March 12, 2008
Publication Date: N/A
Technical Abstract: Benzoxazinoids produced by rye (Secale cereale) can be nematotoxic. To test effects of one of these compounds on nematode population densities, the benzoxazinoid 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA) was added to soil at concentrations ranging from 9.4 to 150 micrograms per ml (dissolved in methanol and water). DIBOA-treated and control soils were inoculated with Meloidogyne incognita and incubated for five days, during which time the soil was sampled at intervals to investigate disappearance of DIBOA and formation of BOA and HBOA, two important metabolites or degradation products of DIBOA. The soil treatments were then planted with cucumber seedlings and grown in the greenhouse for 5 weeks. Disappearance half-life values for DIBOA varied from 14.6 to 24.1 hours. Production of BOA and HBOA were approximately equal and their combined total concentrations never exceeded 10% of the initial DIBOA concentrations. After their initial formation these metabolites also disappeared over the course of the sampling time. Only the highest DIBOA treatment suppressed nematode populations on cucumber roots, with populations approximately 73% of those recorded from the water plus methanol controls. This result was different from the effects previously observed in laboratory assays, in which a lower concentration of DIBOA, 74.3 micrograms per ml, had been sufficient to prevent 50% of eggs from hatching. The fate of DIBOA in soil may account for differences between effects of DIBOA in laboratory assays vs. greenhouse tests.