Ammonium accumulation and ethylene evolution by tomato infected with root‐knot nematode and grown under different regimes of plant nutrition

Ammonium accumulation and ethylene evolution are common phenomena with plant tissues under physiological stress. Enhanced ethylene evolution has been detected with tomato (Lycopersicon esculentum Mill.) infected with root‐knot nematode (Meloidogyne spp.). The present investigation addressed a linkage between ammonium accumulation and ethylene evolution by tomato infected with root‐knot nematode [Meloidogyne incognita Kofoid & White (Chitwood)]. At 6 weeks after infection, an array of foliar symptoms resembling those of ammonium toxicity developed on infected plants. Increased severity of symptoms was accompanied by a concomitant increase in foliar ammonium accumulation and by enhanced ethylene evolution. Stimulation of ammonium accumulation appeared to precede ethylene evolution. Plants grown on different nutritional regimes showed different responses to nematode infection with respect to shoot growth and injury, ammonium accumulation, and ethylene evolution. Relative to nitrate nutrition, ammonium nutrition intensified the injuries and responses from nematode infection.