Cytogenotoxic effects of cypermethrin on root growth: Allium sativum as a model system

Abstract

Cypermethrin is a pyrethroid pesticide used on agricultural farms in Nigeria to control pests of fruits and vegetables but this is highly toxic to aquatic organisms. To determine toxicity of chemicals, Allium cepa is commonly used as an established bioassay however the bulb is used whole. Allium sativum in contrast is able to be split into cloves of smaller units hence this research aims to validate the potential of Allium sativum as a model plant for genotoxicity assessment. In this study, root growth inhibition test and chromosome aberration assay were used and the effective concentration (EC50) of cypermethrin was determined from the root growth curve. Furthermore, the mitotic activities of the root meristem were assessed using light microscopy. Treatment of root meristem of A. sativum with various concentrations of cypermethrin (0.25, 0.50, 0.75 and 1.0 mg/ml) revealed a reduction in the root length and EC50 of 0.44 mg/ml. Also morphological changes such root wilting, dark spots, tenderness of the clove bases and discoloration of the roots were observed. Cytological studies showed a reduction in mitotic index with increasing cypermethrin concentration. Chromosomal aberrations ranging from abnormal metaphases: c-metaphases, disturbed spindles and vagrant metaphases; to abnormal anaphases: laggard chromosomes, chromosome breaks and multipolarities were also recorded. These aberrations reduced with increased concentration of the pesticide leading to the production of lesser number of dividing cells. These show that cypermethrin is genotoxic to the root meristem and A. sativum is a suitable model plant for detecting pyrethroid genotoxicity in plant.