Gradients of salts of the specific ion repellents for Meloidogyne incognita - NH4+, K+, Cl- and NO3- -have been demonstrated to shield tomato roots from infestation in soil. The strategy of these greenhouse experiments was to interpose a salt barrier in a soil column between the plant roots and the nematodes. Potassium nitrate was found to produce a negative chemotaxis for 2nd-stage juveniles of Meloidogyne incognita (J2) as it creates a chemical “shield” around the root system to protect. Tomato seedlings treated with 30 mg/L (3x 10-4 M) KNO3 showed increased plant length and increased root growth without root knot formation after 21 days of incubation with M. incognita J2. Untreated plants were shorter and showed root knot formation. Potassium nitrate outperformed potassium chloride in protection against the root-knot nematode (Table 1).
Table 1. Percentage protection to the number of eggs produced by the root-knot nematode.
Castro, C. E., H. E. McKinney, and S. Lux. 1991. Plant protection with inorganic ions. Journal of Nematology 23.4: 409-413.