The effect of temperature regime and substrate Mn on growth and manganese concentrations in rice

Three rice cultivars, IR712, M1–48 and E425 were grown in solution culture for 10 weeks in temperature controlled glasshouses at IRRI, Los Baños, Philippines. Treatments consisted of two Mn levels, 0.5 and 50 μg.cm^‐3 and two temperature regimes, 35/27 and 20/20 (day/night) in °C. Dry matter and Mn concentrations were determined at 2‐week intervals. In a second experiment, the M1–48 cultivar was grown in solutions containing 0.5, 1, 40 and 80 μg.cm^‐3 Mn at 35/27, 29/21 and 20/20 °C (day/night) temperatures.

It was concluded that rice is more sensitive to excess Mn under cool conditions and that the concentration of Mn in the tissue at which toxicity symptoms appear or growth is decreased depends on the age of the tissues and the environmental conditions under which the plant is growing. Growth of two‐day old seedlings exposed to excess Mn was decreased to a greater degree than was that of 2‐week old seedlings. It is suggested that in screening rice cultivars for tolerance to excess Mn the environmental conditions should be rather rigidly controlled.