MANGANESE TOXICITY IN ECHINOCHLOA-COLONA - EFFECTS OF DIVALENT MANGANESE ON GROWTH AND DEVELOPMENT

Manganese (Mn2+) toxicity is probably the second most important growth -limiting factor (after aluminum toxicity) for plants in acidic soils. The objective of our study was to determine the toxic effects of diff erent concentrations of divalent Mn (MnCl2) on the growth of Echinochl oa colona in hydroponic culture. Seed germination was not inhibited by Mn concentrations of 9.1 to 910 mu M in distilled water. However, the higher Mn concentration (910 mu M) in nutrient solution completely su ppressed root development. Although chlorophyll content decreased with increased Mn concentrations in solution, dry weights of shouts were i ncreased by the higher Mn treatments. These treatments also produced t oxicity symptoms of leaf chlorosis and necrosis. Histological studies showed that the higher Mn concentrations caused disorganization of con ductive and mesophyll tissues.