Untangling the biochemical warfare of plant defence mechanisms against Meloidogyne spp.: a global systematic review with Sub-Saharan Africa insights

MAIN CONCLUSION: Meloidogyne spp. threatens diverse crops, but integrating biochemical resistance markers with agroecological practices and enhanced SSA research capacity is crucial for sustainable nematode management. Root-knot nematodes (Meloidogyne spp.) pose a major threat to global agriculture, especially in Sub-Saharan Africa (SSA), where smallholder farming systems predominate. Their impact is frequently underestimated due to difficulties in diagnostic challenges and symptom overlap with other stresses. This systematic review critically examines 30 experimental studies conducted across 17 countries, 25 from other regions and 5 from SSA, examining plant biochemical defence responses against Meloidogyne spp., with an emphasis on SSA while incorporating global data. Literature was sourced from PubMed, Web of Science, Scopus, and AGRIS using strict inclusion criteria. Findings show that among the SSA studies included in this review, enzymatic assays were commonly employed on staple crops like maize, yam, and tomato in controlled environments, whereas global studies apply chromatographic metabolite profiling and molecular or omics-based analyses. Resistance and tolerance were consistently linked to elevated peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activity, phenolic accumulation, and activation of key phytohormone pathways (salicylic acid, jasmonic acid, and ethylene). However, major limitations identified include methodological heterogeneity, limited field validation, and underrepresentation of indigenous crops in SSA. The review highlights the urgent need for standardised protocols and expanded molecular capacity. Integrating biochemical markers into breeding programmes may support the development of region-specific resistance screening, and future sustainable nematode management strategies through interdisciplinary collaboration is essential for sustainable nematode control, although further field validation remains necessary. This synthesis offers a foundation to guide future research, crop improvement, and policy decisions under climate stress.