Growth and physiological responses of okra (Abelmoschus esculentus (L.) Moench ) to simulated acid rain and root-knot nematode (Meloidogyne incognita)

S. S. Shaukat, M. A. Khan


This investigation was undertaken to ascertain the single and combined effects of simulated acid rain (SAR) and the root knot nematode (RKN), Meloidogyne incognita, on okra. Root knot nematode inoculated and uninoculated plants were intermittently exposed to SAR (pH 4.0). In combined treatment, plants were exposed to SAR either concomitantly with or a week after inoculation. SAR exposure either alone or in combination with nematodes caused white-to-tan spots on the abaxial and adaxial surfaces of leaves. Single and combined treatments with M. incognita and SAR significantly suppressed pigment synthesis, shoot and root dry weights and yield of okra. Reducing and non-reducing sugars were depleted to varying degrees in all treatments. Non-reducing sugars were reduced to a greater extent than were the reducing sugars. This effect was more pronounced when the plants were treated with SAR and infected with root-knot nematode. SAR exposure, either alone or in combination with M. incognita, resulted in accumulation of soluble phenols, possibly as an induced defence mechanism against abiotic and biotic stresses. The fecundity of M. incognita was markedly suppressed in plants exposed to SAR as compared with those infected with M. incognita alone. The results are discussed in the light of pathological and physiological responses of plants to pathogens. Apparently, SAR and the nematode interacted additively and synergistically (reduction of chlorophyll and increase of soluble phenol contents) as their combination caused greater damage to okra than single treatments, especially when there was a post-inoculation exposure to SAR.

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