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Abstract
Most land plants can become infected by plant parasitic nematodes in the field. Plant parasitic nematodes can be free-living or endoparasitic, and they usually infect plant roots. Most damaging are endoparasites, which form feeding sites inside plant roots that damage the root system and redirect nutrients towards the parasite. This process involves developmental changes to the root in parallel with the induction of defense responses. Plant flavonoids are secondary metabolites that have roles in both root development and plant defense responses against a range of microorganisms. Here, we review our current knowledge of the roles of flavonoids in the interactions between plants and plant parasitic nematodes. Flavonoids are induced during nematode infection in plant roots, and more highly so in resistant compared with susceptible plant cultivars, but many of their functions remain unclear. Flavonoids have been shown to alter feeding site development to some extent, but so far have not been found to be essential for root–parasite interactions. However, they likely contribute to chemotactic attraction or repulsion of nematodes towards or away from roots and might help in the general plant defense against nematodes. Certain flavonoids have also been associated with functions in nematode reproduction, although the mechanism remains unknown. Much remains to be examined in this area, especially under field conditions.
Highlights
Introduction to Plant Parasitic NematodesNematodes are small roundworms with a bilateral symmetry and unsegmented bodies [1].Whilst most nematodes are free-living, ~7% (>4100 species) of the characterized nematodes belong to the plant-parasitic nematode (PPN) group [2,3,4]
PPNs are agricultural pests that cause significant crop damage and crop loss, estimated at up to $US 125 billion globally per annum [4,5,6,7]. This is due to the diversion of host nutrients to PPNs and interference with transport processes, as well as physical damage caused during feeding or migration, which can result in secondary infections [8,9]
We suggest that flavonols such as kaempferol, quercetin and their glycosides would be likely used by these nematodes for auxin regulation as they have been shown to inhibit polar auxin transport [94,97,98]
Summary
Nematodes are small roundworms with a bilateral symmetry and unsegmented bodies [1]. Whilst most nematodes are free-living, ~7% (>4100 species) of the characterized nematodes belong to the plant-parasitic nematode (PPN) group [2,3,4]. PPNs are agricultural pests that cause significant crop damage and crop loss, estimated at up to $US 125 billion globally per annum [4,5,6,7]. PPNs are classified into three orders—the Triplonchida, Dorylaimida, and Tylenchida—with the majority of agriculturally damaging nematodes belonging to the last order [10]. These PPNs have evolved a highly specialised feeding structure, termed the stylet, to feed on plant tissues, and often display complex life-stages to suit their environment [11,12,13]. The tylenchids are classified based on their trophic niche, either as aerial nematodes or root parasitic nematodes [10]
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