Assessment of phytotoxicity of selected botanical insecticides on treated cowpea (Vigna unguiculata) seed

Abstract

Background Synthetic insecticides employed in seed treatment are often phytotoxic, especially at slightest misapplications. Cowpea seed is mainly attacked by Callosobruchus maculatus. It is established that azadirachtin, myristicin and α-humulene based insecticides (botanical insecticides) are eco-friendly and have activity against C. maculatus and thus are considered ideal candidates in research efforts targeted at developing plant based options for protecting cowpea seed against C. maculatus attack. Therefore, the aim of this study was to evaluate the toxicity of selected botanical insecticides on treated cowpea (Vigna unguiculata) seed. Results Electrical conductivity of leachate obtained from cowpea seed treated with botanical insecticides was significantly (P < 0.05) lower than that recorded on seed treated with chlorpyrifos. Malondialdehyde levels in seed of cowpea cultivars; SAMPEA 11 and 12 was significantly (P < 0.05) higher than that recorded on seed treated with chlorpyrifos. However, malondialdehyde levels in seed of SAMPEA 14 treated with myristicin and azadirachtin based insecticides were not significantly (P > 0.05) different from that reported for cowpea seed treated with chlorpyrifos. Less than 50% of the embryo recovered from seed treated with botanical insecticides was unstained contrary to the observation made on seed of SAMPEA 14 dressed with chlorpyrifos. Conclusion This study reveals similarity as well as variation in varietal sensitivity to phytoxicity among the various cultivars of cowpea seed studied implying that a farmer’s choice of botanical insecticides for the protection of cowpea seed against Callosobruchus maculatus would strictly depend on the cultivars involved.