Monitoring of phytotoxicity of lead and mercury from germination and early seedling growth indices in two rice cultivars

Treatment of seeds of two rice (Oryza sativa L.) cultivars (Ratna and IR36) separately with 10(-5) and 10(-4) M PbCl2 and HgCl2 decreased germination percentage, germination index (GI), shoot and root length, tolerance index (TI), vigour index (VI) and dry mass of shoot and root but increased percentage difference from control (% DFC) of germination and percentage phytotoxicity in both the cultivars. It was observed from these indices that the phytotoxic effect of mercury was greater than lead at identical concentrations and that IR36 appeared more tolerant than Ratna to these metals. Among the monitoring indices examined, TI, VI, and % phytotoxicity seemed to serve as good biological monitoring methods for evaluating the relative toxicity of lead and mercury to rice cultivars.