Boron toxicity in young cassava plants

Abstract

Listen

Translate article

Diagnosis of boron (B) toxicity in cassava grown in soil is still a challenge. The objectives of this work were (i) to describe the symptoms of B toxicity in cassava grown in soil and (ii) to establish critical B toxicity concentrations in soil and leaf blades of the plant. In a greenhouse, plants were grown for 68 days in pots filled with sandy soil samples submitted to B rates of 0, 0.5, 1, 2, and 4 mg dm−3. Application of B increased both concentration of B extracted from the soil with hot water and B concentration in leaf blades. Visual symptoms of B toxicity were only observed in the highest rate of applied B. The symptoms were photographed and described as chlorosis followed by necrosis in the tip and margin of older leaves. Despite the symptoms, there were no significant effects on growth of the plant. As a result, critical concentrations could not be obtained. Alternatively, thresholds based on B toxicity symptoms are suggested. The thresholds for concentration of B in younger leaf blades and older leaf blades were calculated to be 99.9 and 130.7 mg kg−1, respectively. These respective thresholds corresponded to the thresholds for B concentrations in soil of 0.875 and 0.891 mg dm−3. Concentrations above these thresholds could be used to support visual diagnosis of suspected B toxicity symptoms. Photos, description, and thresholds provided in this article can help improve the diagnosis of visual B toxicity symptoms in young cassava plants grown in soil.