Eco-friendly Approaches to the Management of Plant-Parasitic Nematodes

Abstract

Eco-friendly approaches have been increasingly used for the management of plant-parasitic nematodes because of growing worldwide concern regarding health risks and environmental contamination caused by nematicides. Avoiding the introduction and spread of nematodes to non-infested areas is the most efficient method of control. Cleaning machinery and equipment, use of healthy planting materials, and quarantine procedures are good examples of preventive practices. In infested fields, nematode populations can be reduced by combining cultural, physical, and biological methods and genetic resistance of plants. The use of resistant crops is one of the most efficient and eco-friendly methods for reducing losses caused by plant-parasitic nematodes. Based on the information on which nematode species/races are prevalent in the field, the grower should choose a resistant crop, when available. Soil plowing and irrigation – named humid fallow – have been used for the management of root-knot nematodes in common bean (Phaseolus vulgaris), lettuce (Lactuca sativa), and okra (Abelmoschus esculentus) in Brazil. Soil steaming, treatment of planting materials with hot water, and soil solarization are recommended for the control of several plant-parasitic nematode species, based on the lethal action of high temperatures. Biofumigation with residues from some species of Brassicaceae and manures releases volatile toxic gases during the degradation process of the organic matter, including isothiocyanates. Non-host or antagonistic plants are also important tools for the integrated management of nematodes. In this context, marigolds (Tagetes erecta and T. patula), crotalaria (Crotalaria spectabilis), sunn hemp (Crotalaria juncea), and velvet bean (Mucuna pruriens) are widely used as antagonistic plants. Soil amendment with crop residues of neem (Azadirachta indica), castor bean (Ricinus communis), velvet bean (Mucuna pruriens), crotalaria (Crotalaria spectabilis), and Brassica spp.; oil seed cakes of neem, castor bean, mustard, and sesame; cattle manure; poultry litter; liquid swine manure; and crab shells release nematotoxic substances during decomposition, provide nutrients to the plants, and increase the population of biocontrol agents. More than 200 species of nematode antagonists have been identified, including fungi, bacteria, nematodes, tardigrades, and collemboles. Fungi and bacteria are the most studied and commercially exploited organisms for nematode control. Several commercial bionematicides have been developed from the nematode-trapping fungi Arthrobotrys, Dactylaria, Dactylella, and Monacrosporium, the egg-parasitic fungi Purpureocillium lilacinum and Pochonia chlamydosporia, the antibiotic bacterium Bacillus species, and the obligate parasite bacterium Pasteuria spp. The anaerobic soil disinfestation is an ecological alternative to soil fumigation for the control of several soilborne pathogens, including nematodes. This technique consists of incorporating organic material that is easily decomposable (C/N ratio from 8 to 20:1) into the soil, irrigating to saturation, and covering the soil with oxygen-impermeable plastic. Accumulation of toxic products from anaerobic decomposition, antagonism by anaerobic organisms, lack of oxygen, and the combination of all of them are the main drivers that explain the efficacy of anaerobic soil disinfestation. Consumers have been demanding higher food security and environmental quality, and this situation will not be different in the future. In this context, scientists’ efforts in discovering new nonchemical strategies for nematode control and improvements in the current methods must be continuous.