SURVEY OF PLANT-PARASITIC NEMATODE COMMUNITIES, TROPHIC STRUCTURE AND SOIL CHEMICAL PROPERTIES IN CITRUS ORCHARDS IN THE MEKONG DELTA

Abstract

Plant-parasitic nematodes are among the most harmful constraints to citrus production. This study was conducted in three provinces of the Mekong delta (Vinh Long, Tra Vinh and Dong Thap provinces), with a total of 134 soil samples collected from lemon, orange, tangerine and pomelo orchards. The objectives were to assess plant-parasitic nematodes composition, nematode trophic structure and soil chemical properties in citrus-based farming systems. Nematode densities varied greatly among provinces and crops, ranging from 212 to 928 individuals per 100 g of dry soil, with the highest in Tra Vinh province and the lowest in Dong Thap province. Orange and lemon orchards harbored higher nematode densities compared to tangerine and pomelo. Bacterivores dominated the trophic structure, followed by plant-parasitic and fungivorous nematodes, with an unusually high proportion of fungivores in orange soils. A total of 13 genera/species of plant-parasitic nematodes composition were recorded. Aphelenchus was the most prevalent (73 individuals/100 g soil, 69.4% frequency), followed by Tylenchulus semipenetrans and Aphelenchoides. Species distribution varied with crops, with orange soils containing the highest diversity (11 genera). Healthy orchards were generally associated with bacterivores and fungivores, while poor growth was linked to Pratylenchus, Meloidogyne, Rotylenchulus and Helicotylenchus. Soils were moderately to strongly acidic, low in organic carbon (2 - 4%), with variable nitrate-N and excess phosphorus in some orchards. Correlation analýis revealed close associations between T. semipenetrans and bacterivores with nitrate-N, Aphelenchoides with EC, nitrate-N and available N and predators with available phosphorus. These findings provide important insights into nematode ecology and soil–nematode interactions in citrus systems of the Mekong delta.