Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/4/2005
Publication Date: 10/1/2005
Citation: Zasada, I.A., Meyer, S.L., Halbrendt, J.H., Rice, C. 2005. Activity of hydroxamic acids from secale cereale against the plant-parasitic nematodes meloidogyne incognita and xiphinema americanum. Phytopathology 95:1116-1121. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plants and cause ten billion dollars in crop losses annually in the United States. Farmers face an enormous problem because they lack safe and effective ways of reducing the numbers of nematodes in soils. Cover crops are crops planted to control soil erosion or to improve soil quality. They are an important component of crop production systems and have the potential to control plant-parasitic nematodes. Therefore, in this study, two agriculturally destructive species of nematodes were exposed in laboratory tests to four chemicals produced by a widely-used cover crop, rye. The four compounds differed in their toxicity to the nematodes tested. In addition, the two nematode species differed in their susceptibility to the different compounds. These results are significant because they provide the first identified chemical factors that are partly responsible for the toxicity of rye to nematodes. This research will be used by scientists developing the use of rye cover crops for reducing nematode numbers in agricultural fields.
Technical Abstract: Cyclic hydroxamic acids are secondary metabolites found in the Poaceae and have been implicated in the allelopathy of rye (Secale cereale). The toxicity of these compounds against plant-parasitic nematodes is unknown. DIBOA (2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one) and DIMBOA (2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one) and their degradation products BOA (benzoxazolin-2(3H)-one) and MBOA (6-methoxy-benzoxazolin-2(3H)-one) were screened against Meloidogyne incognita second-stage juveniles (J2) and eggs and mixed-stage Xiphinema americanum. Xiphinema americanum was more sensitive to DIBOA and DIMBOA than M. incognita J2 with a maximum mortality of 96 and 92% compared to 73 and 72% at 90 µg/ml. The egg stage of M. incognita was less sensitive to the hydroxamic acids than the J2 stage; only DIBOA resulted in a 50% reduction in egg hatch with a lethal concentration (LC50) value of 74 µg/ml compared to 21 µg/ml for the J2 stage. When M. incognita J2 were treated with DIBOA for 48 h and the treatment was removed and replaced with water, the LC50 increased from 21.0 to 40.7 µg/ml. MBOA was not toxic to X. americanum or M. incognita eggs, but was toxic to M. incognita J2 with LC50 values of 44 and 20 µg/ml before and after rinse. BOA was the least toxic hydroxamic acid tested; it did not reduce M. incognita egg hatch after one week of exposure or affect the mortality of X. americanum a 24h exposure period. Knowledge of the toxicity of the chemical components of rye provides a valuable starting point for improving the suitability of this cover crop for plant-parasitic nematode suppression.