Effects of the root-knot nematode, Meloidogyne incognita, on the sensitivity of tomato to sulfur dioxide and ozone

Infection of plants with root-knot nematode leads to an increase in transpiration rate. We hypothesize that, in infected plants, the diffusive intake of gaseous pollutants would be greater and the interaction between the nematode and pollutant(s) would be governed by the degree of stomatal opening. Tomato plants infected with the root-knot nematode, Meloidogyne incognita were exposed to air containing 0, 50 or 100 ppb of SO2 or O-3 for 5 h every third day on 27 occasions in 1988 and 1989. Plants exposed to the gases at 100 ppb had chlorotic and/or necrotic leaves, small shoots and roots, reduced leaf pigment levels and low yield, compared to untreated plants. Greater foliar injury developed on plants exposed to SO2 + O-3 mixture. Symptoms were even greater on nematode-infected exposed plants. M. incognita alone reduced tomato yield by 14.4% and induced a 3.6% increase in the width of stomatal pores and a 15.6% increase in the transpiration rate. A positive correlation was observed between stomatal pore width and rate of transpiration. Interaction between SO2 and O-3 depended on the presence (significant) or absence (insignificant) of nematodes. Most effects of nematode infection and gas exposures (especially mixtures) were synergistic. Disease intensity (galls per root system) was increased, but nematode reproduction (egg masses per root system, eggs per egg mass) reduced on plants exposed to SO2 and/or O-3. (C) 1997 Elsevier Science B.V.