BORON NUTRITION OF CASSAVA, AND THE BORON-X TEMPERATURE INTERACTION

Rooted stem tip cuttings of five cassava cultivaes grew well in a complete nutrient solution containing 46 μM boron when the solution temperature was maintained at 28 or 33°C, but developed severe boron deficiency symptoms at 18°C. Mild symptoms of boron deficiency were observed also at a solution temperature of 23°C. The diagnosis of boron deficiency was confirmed both by plant analysis and by the induction of identical symptoms in a subsequent experiment in which the solution temperature was held constant at 25°C and the boron supply varied. In this latter experiment with cv. Mameya, the critical boron concentration in the plant tops for deficiency was estimated at about 17 μg.g-1 dry weight and that for toxicity at about 140 μg.g-1 dry weight. The boron x temperature interaction in cv. Mameya and Seda was further explored over the temperature range 19-40°C with four levels of boron supply ranging from deficient to toxic. It was found that the susceptibility of cassava to boron deficiency at suboptimal root temperatures was due in part to a lowering of the rate of boron uptake per unit root weight and in part to a reduction in the relative size of the root system. © 1979.