Salicylic acid-induced suppression of Meloidogyne incognita infestation of okra and cowpea

Salicylic acid (SA) applied as 10 mM foliar spray to okra (Abelmoschus esculentus) cv. Purbani Kranti and cowpea (Vigna unguiculata) cv. Pusa Ruby plants 24 h before inoculation of roots with Meloidogyne incognita juveniles, reduced infestation. Salicylic acid had no direct influence on plant growth and did not kill nematodes in an in vitro test. It induced increased accumulation of a 14 kDa pathogenesis-related protein (PR-1) in roots of both non-inoculated and inoculated salicylic acid-sprayed okra but not in the treated leaves. Salicylic acid sprays enhanced pherylalanine ammonia lyase (PAL) activity in roots of both non-inoculated and inoculated cowpea, estimated at 15 days after inoculation. Infected roots had higher PAL activity than roots of the corresponding non-inoculated treatments. Both PAL activity and SA-induced resistance gradually declined with plant age after treatment.