Effect of root-knot nematode and two species of crown gall on antioxidant activity of grape leaves

Agrobacterium tumefaciens and Agrobacterium vitis significantly reduced the entire criteria (galls, embedded stages, final population, Pf/Pi and egg production) of the root-knot nematode, Meloidogyne incognita, when they were in concomitance with grape (Vitis vinifera var) superior roots. Greater suppression in such criteria was observed with high inoculum levels (5X10(7) cfu/pot) than with lower (2.5X10(7) cfu/pot) ones. All treatments resulted in the increase of leaves contents of H2O2 and lipid peroxidation (TBARS) dramatically, which were considered the most damaging stresses in plant cells. The contents of AsA, GSH, TPH and PAL specific activity increased as a strongly antioxidant defense compound against induced oxidative damage. In addition, the increase in the activity of various antioxidant defense specific enzymes (SOD, APX, CAT and GST) represented the protective activity used to counteract the oxidative injury promoted by nematode and nematode-bacteria infections. The rate of the chemical increase was significantly higher in interaction treatments than in the leaves of plants treated singly with M. incognita. Moreover, higher inoculum levels resulted in higher values of the measured chemicals. Symptoms appearance at low levels of nematode and bacterial treatments were significantly preceded by significant induction of AsA, GSH and TPH contents, and APX, CAT, SOD, GST and PAL activities in grape leaves. However, under high levels of nematode and bacteria, an obvious depletion at all non-antioxidants enzymes' levels and antioxidants enzymes' activities was observed. It is supposed that stimulated antioxidative processes contributed to the suppression of necrotic symptom development in grape leaves depending on the level of pathogen inoculum.