Side effects of biostimulants against root-knot nematodes on tomato

Plant biostimulants are often reported for their suppressive side effects against root-knot nematodes, due to an enhancement of host-plant resistance or to direct nematoxicity. Effects of soil treatments with four different commercial biostimulants based on quillay extract, sesame oil, neem seed cake or algae were investigated against the root-knot nematode Meloidogyne incognita on tomato in potting mixes. Infested soil, either untreated or treated with Oxamyl, and uninfested soil were used as controls. Numbers of nematode eggs and juveniles and gall formation on tomato roots and plant fresh top and root weight were checked at 75 days after transplanting. Treatments with neem cake, sesame oil and quillay extract formulations resulted in a significant reduction of nematode multiplication and gall formation on tomato roots compared with untreated controls, and were not significantly different from treatment with Oxamyl. Neem cake and sesame oil were also significantly more suppressive than the quillay extract formulation in the first experiment. The algae formulation provided the lowest effect on nematode infestation, causing only a slight significant reduction of eggs and galls on tomato roots only in the first experiment. Almost all treatments with the four biostimulants also significantly increased tomato plant growth, though the best growth effect was always provided by the quillay formulation. Results from these experiments seem to indicate that biostimulants may play a role in sustainable nematode management strategies, either by limiting nematode impact on plant growth and/or by directly suppressing multiplication.