Nematodes as indicators of sustainable soil health management practices in corn-soybean production

Soil nematodes are multicellular organisms causing significant economic and ecological impacts, and their community composition is widely used as a bioindicator of soil health. Current methodologies for nematode assessment require further refinement and advancement. This thesis addressed knowledge gaps by combining enhanced DNA metabarcoding tools with the standard morphological analyses to evaluate soil nematode communities under different crop management practices. The first study evaluated the use of soil DNA for profiling nematode communities. Compared to the commonly used NF1/18Sr2b primer, degenerate primers (NemF/18Sr2b and NemFopt/18Sr2bRopt) combined with an improved soil DNA extraction protocol greatly increased nematode detection and taxonomic resolution. The enhanced primer specificity enabled the recovery of nematode assemblages from soil DNA, and was comparable to those from nematode DNA. The direct nematode DNA extraction yielded consistent community profiles regardless of the primer used. This demonstrates that DNA source and primer choice can bias biodiversity estimates. These findings suggest that the widely used NF1/18Sr2b primer may have contributed to the commonly held perception that soil DNA extraction is not a reliable method for studying nematode communities. The second study compared morphological identification with DNA metabarcoding for nematode community analysis. Metabarcoding revealed a greater diversity of beneficial free-living bacterivores, detecting many rare taxa that were overlooked by conventional microscopy. In contrast, the morphological approach provided accurate identification and quantification of herbivore populations, while metabarcoding overrepresented bacterivorous nematodes. Both methods were able to identify key indicator taxa, but also missed others. The inherent differences between molecular and morphological methods, however, prevented alignment of results. The third study examined how winter cover crops (WCCs) in a corn–soybean rotation influence nematode communities and soil health indicators. The study observed that long-term use of WCCs significantly increased total nematode abundance and diversity, while reducing the prevalence of herbivorous nematodes, relative to fallow. Mixed-species WCCs promoted nematode communities that were more balanced and biologically enriched than those of a single species. The fourth study demonstrated that conservation tillage practices (occasional tillage within no-tillage and minimum tillage) increased beneficial free-living nematodes and soil organic matter. In contrast, conventional tillage resulted in higher populations of herbivores such as Pratylenchus sp. in deeper soil layers. Over time, occasional tillage within no-tillage systems developed higher soil food web indices and shifted toward communities driven by fungi and herbivorous nematodes

Name thesis:degree_name

Ph.D. Biological Sciences

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Faculty of Mathematics and Science

Department dc:contributor.department

Department of Biological Sciences

Grantor dc:publisher

Brock University

Year dc:date.issued

2026

Author dc:creator

• Akanwari, Jerry

Advisors dc:contributor.advisor

• Sultana, Tahera
• Liang, Ping

• NATURAL SCIENCES::Biology

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10464/19957

OAI identifier oai:identifier

oai:brocku.scholaris.ca:10464/19957