DIBOA: Fate in Soil and Effects on Root-knot Nematode Egg Numbers

Authors: Meyer, Susan; Rice, Clifford; Zasada, Inga

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2009
Publication Date: 5/5/2009
Citation: Meyer, S.L., Rice, C., Zasada, I.A. 2009. DIBOA: Fate in Soil and Effects on Root-knot Nematode Egg Numbers. Soil Biology and Biochemistry. 41:1555-1560.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that cause ten billion dollars in U.S. crop losses annually, and root-knot nematodes are among the most destructive species on many crops. A major problem facing growers is the lack of safe and effective methods for reducing crop losses caused by root-knot nematodes. Therefore, scientists are developing the use of rye as a crop for suppressing nematodes after the rye plants are incorporated into soil. Because rye produces a compound called DIBOA that is believed to naturally control nematodes, this study investigated the persistence of different concentrations of DIBOA when applied to soil and their effects on nematode control. The results indicated that only the highest DIBOA concentration reduced nematode population densities, and that little DIBOA was recovered after 5 days. The results are significant because they demonstrated that high soil concentrations of DIBOA are necessary to suppress root-knot nematodes (probably in part because the compound disappears quickly after addition); therefore, DIBOA may not be a major factor in the ability of rye crops to suppress this nematode. This research will be used by scientists developing environmentally safe methods for managing diseases caused by nematodes.

Technical Abstract: The benzoxazinoid 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) is produced by rye (Secale cereale) and may contribute to plant-parasitic nematode suppression when rye plants are incorporated as a green manure. We investigated the fate of DIBOA in soil and DIBOA’s effects on nematode reproduction. Soil in plastic bags was treated with DIBOA at concentrations ranging from 1.1 to 18 micrograms g-1 dry soil, and with the root-knot nematode Meloidogyne incognita. Control soils were treated with water or with 0.31% methanol, with or without nematodes. DIBOA concentrations extracted from the soil were measured at selected times for 5 consecutive days. The soil from each bag was then placed into a pot in the greenhouse, and a cucumber seedling was transplanted into each pot. Five weeks later, only the highest DIBOA concentration, 18 micrograms g-1 soil, reduced nematode egg numbers. At 0 h, DIBOA measured in soil ranged from 19.68 to 35.51% of the initial DIBOA concentration, and was dependent on the concentration added to the soil. DIBOA half-life was from 18 to 22 h, and very little DIBOA was present in soil after 120 h. Identified breakdown products accounted for only 4% at maximum of the initially added DIBOA. The results of our study demonstrate that high soil concentrations of DIBOA are necessary to suppress M. incognita; DIBOA may not be a major factor in nematode suppression by a rye cover crop.