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

A study was undertaken in order to investigate the effects of SO₂ (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 J₂ of M. incognita. SO₂ 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 SO₂ at 50 or 75 ppb concentrations. The nematode and SO₂ interaction varied with the levels of SO₂ and the response of the plant to M. incognita. SO₂ at 50 or 75 ppb concentrations stimulated the pathogenesis of M. incognita on cucurbit species. The combined effect of 75 ppb SO₂ and M. incognita suppressed plant length by 34% against the sum of decreases observed by M. incognita and SO₂ individually (14-18%). At 50 ppb SO₂, the fecundity of M. incognita was decreased and combined effect of SO₂ 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 SO₂.