Phytotoxicity of pesticides mancozeb and chlorpyrifos: correlation with the antioxidative defence system in Allium cepa.

Pesticides are a group of chemical substances which are widely used to improve agricultural production. However, these substances could be persistent in soil and water, accumulative in sediment or bio-accumulative in biota depending on their solubility, leading to different types of environmental pollution. The present study was done to assess the impact of pesticides-mancozeb and chlorpyrifos, via morphological and physiological parameters using Allium cepa test system. Phytotoxic effects of pesticides were examined via germination percentage, survival percentage, root and shoot length, root shoot length ratio, seedling vigor index, percentage of phytotoxicity and tolerance index. Oxidative stress on Allium seedlings caused by pesticides was also assessed by investigating the activity of antioxidative enzymes viz. catalase, peroxidase and superoxide dismutase. Correlation was worked out between morphological parameters and antioxidative enzymes to bring out the alliance between them. Mancozeb and chlorpyrifos concentrations were significantly and positively correlated with the activity of antioxidative enzymes and negatively correlated with morphological parameters. Significant positive correlation between various morphological parameters showed their interdependency. However, negative correlation was obtained between activity of antioxidative enzymes and morphological parameters. The enzymes however, showed positive correlation with each other. Based on our result we can conclude that all morphological parameters were adversely affected by the two pesticides as reflected by phytotoxicity in Allium. Their negative correlation with activity of antioxidative enzymes indicates that upregulation of antioxidative enzymes is not sufficient to overcome the toxic effect, thereby signifying the threat being caused by the regular use of these pesticides.

Monitoring of morphotoxic, cytotoxic and genotoxic potential of mancozeb using Allium assay.

The present experiment was designed to monitor the morphotoxic, cytotoxic and genotoxic potential of Mancozeb (fungicide) in non-target plants using bulbs of Allium cepa. Mancozeb is classified as a contact fungicide and is registered for use on a variety of crop plants. In the present monitoring, Allium cepa bulbs were exposed to different concentrations of mancozeb viz., 10, 30, 50, 70, 90, 110, 130 and 150 ppm for 24 and 48 h. The potential morphotoxic and cytotoxic effects of mancozeb were examined by determining the average root number, average root length, mitotic index, relative abnormality rate (%) and frequency of abnormalities (%). A progressive significant concentration and time dependent inhibition of the average root number, average root length indicated the morphotoxic nature. The cytotoxic effect was significantly increased for 48 h treatment as compared to 24 h treatment time, by reducing the mitotic index of meristematic cells. The results indicated an indirect genotoxic effect by inducing different types of chromosomal abnormalities, likely sticky, disoriented and fragmented chromosomes. Thus indicating that the investigated fungicide have genotoxic potential due to abnormal DNA condensation and chromosome coiling by spindle inactivation. The observations of cyto and genotoxic effects suggest that the fungicide mancozeb is clastogenic agent. Thus the different concentrations used in the field could be harmful for the end-receptors of food-chain and needs constant monitoring and management for the better development of crop plants.