Factors determining the variability of performance of bio-control agents against root-knot nematodes in vegetable plants

The application of management strategies against plant-parasitic nematodes (PPNs), an alternative to the use of toxic nematicides, has become of paramount importance due to the recognized environmental impact. Pre-treatments with bio-control agents (BCAs), such as bio-control fungi (BCF, Trichoderma spp.) and arbuscular mycorrhizal fungi (AMF), have been proved to protect many crop plants from endoparasitic sedentary nematodes (ESNs), the most damaging PPN group. However, the use of commercial BCA formulates is not always successful because of an array of variables that influence their performance. One AMF-based and 2 BCF-based commercial formulates were used as soil-drench pre-treatments to protect tomato, egg, and pepper plants from ESN attack. High variability of performance occurred according to the growth stage of treated plants and the amounts of formulates provided per plant. All formulates were highly effective in reducing both root-knot (RKN) and potato cyst (PCN) nematode infection when plants had reached an intermediate growth stage (3.5-5 g plant weight at treatment). However, only specific ranges of doses had to be used. Lower doses were ineffective against nematode attack, higher doses were often toxic to plants. When plants were grown from seeding in BCA-enriched soil, priming against RKNs was even more active. If plants were not challenged by nematodes, BCAs had a low bio-fertilizer effect.