Biological and Physiological Responses of Root-knot Disease Development on Five Cucurbits Exposed to Different Concentrations of Sulfur Dioxide

A study was undertaken in order to investigate the effects of SO(2) (25, 50, and 75 ppb) exposure for five hours on alternate days for three months on the susceptibility of five cucurbits to the infection of Meloidogyne incognita, causing root-knot disease. Four-week-old cucurbit plants were inoculated with 2000 J(2) of M. incognita. SO(2) levels of 50 and 75 ppb caused noticeable injury to foliage and reduced the plant growth parameters and biomass production of cucurbits (p ≤ 0.05). Nematode-inoculated plants caused characteristic oval, fleshy and large galls. The galls were formed closely, and as a result they coalesced, giving bead-like impressions especially in pumpkin and sponge gourds. Disease severity became aggravated on plants exposed to SO(2) at 50 or 75 ppb concentrations. The nematode and SO(2) interaction varied with the levels of SO(2) and the response of the plant to M. incognita. SO(2) at 50 or 75 ppb concentrations stimulated the pathogenesis of M. incognita on cucurbit species. The combined effect of 75 ppb SO(2) and M. incognita suppressed plant length by 34% against the sum of decreases observed by M. incognita and SO(2) individually (14–18%). At 50 ppb SO(2), the fecundity of M. incognita was decreased and combined effect of SO(2) and M. incognita was more than the sum of their singular effects. The study has proven that root-knot disease might become aggravated in the regions contaminated with elevated levels of SO(2).