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Journal of Biological Sciences

Year: 2007 | Volume: 7 | Issue: 7 | Page No.: 1221-1226
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Authors

D.L. Coyne

E.O. Oyekanmi

Keywords

Research Article

Symbiotic Nitrogen Fixation of Two Soybean Genotypes as Affected by Root-Knot Nematode and Microsymbionts

D.L. Coyne and E.O. Oyekanmi
The ability of soybean to symbiotically fix Nitrogen (N) was found to be substantially reduced (p≤0.05), after inoculation with root-knot nematode (Meloidogyne incognita). Galling, which is a commonly used indicator of root-knot crop damage, may provide less accurate information about reductions in the symbiotic N fixation of soybean. The experiments were undertaken in Nigeria in pots, using two soybean genotypes (TGx 1448-2E and TGx 1485-1D) with differential susceptibility to nematode. The microsymbionts Glomus mosseae (200 spores), Bradyrhizobium japonicum (106 cells mL1) and Trichoderma pseudokoningii (6.8x107 spores) were applied plant1. Treatments involving nematode inoculation had 1000 second-stage juveniles plant1. Ureide N (fixed N) in stems and petioles, nodulation score and activity, nematode infection and arbuscular mycorrhizal colonization were assessed at harvest using standard methods. Regression and correlation analyses demonstrated that root nematode densities assessed at harvest were highly correlated negatively (p≤0.001) with Symbiotic N Fixation (SNF) as measured from the ureide N. Results confirmed that inoculation of M. incognita reduced SNF, nodulation score, nodule activity and plant growth parameters. However, fixed N was not necessarily related to galling damage. Results indicated that nodulation score and galling may not be the most suitable parameters, by which levels of productivity or damage could be determined in the presence of Meloidogyne sp., but rather ureide N is a more accurate assessment of the effect of M. incognita on soybean.
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