Biological control of plant-parasitic nematodes in citrus: Exploiting fungi, bacteria, and mycorrhizal symbiosis with emphasis on mechanisms of action

Citrus trees face significant challenges from various plant-parasitic nematodes (PPNs), with Tylenchulus semipenetrans being especially problematic due to its widespread occurrence in all citrus-producing regions, resulting in considerable economic losses for growers (up to 30–50 % yield loss in heavily infested orchards). This review provides a comprehensive overview of the major nematode pests affecting citrus trees, focusing on the biology, life cycle, and biotypes of T. semipenetrans , as biotype variation governs host specificity, modulates interactions with the soil microbiome, and determines the effectiveness of biological control strategies. It also highlights interactions with soil microorganisms and their ecological significance. Moreover, the review explores biological control agents such as fungi, bacteria, and arbuscular mycorrhizal fungi (AMF), as well as the use of resistant rootstocks, with a particular focus on their mechanisms of action. Specifically, it addresses key biocontrol agents such as Trichoderma spp. and Purpureocillium lilacinum , which have shown promising nematicidal activity. Additionally, it discusses the integration of nematode management into comprehensive pest and disease control frameworks, examines regulatory considerations governing the deployment of biological control agents, and identifies key knowledge gaps requiring further investigation. Finally, it explores the potential effects of climate change on the distribution, survival, and population dynamics of PPNs. It also highlights emerging molecular techniques, such as RNA interference (RNAi) and CRISPR, as promising tools for future nematode management strategies. • Tylenchulus semipenetrans is the main PPN affecting citrus trees globally. • Three biotypes of T. semipenetrans show host specificity and geographic range. • This nematode disrupts citrus growth by damaging roots and altering physiology. • Biological control reduce T. semipenetrans impact.