BORON DEFICIENCY AND CHILLING INJURY INTERACTIONS IN TOBACCO TRANSPLANTS GROWN IN THE FLOAT SYSTEM

Abstract

Boron deficiency and chilling injury produce similar symptoms in young tobacco transplants. Mistaken identification of chilling injury as B deficiency has resulted in B toxicity when growers apply additional B to non-deficient plants. In order to distinguish between B deficiency and chilling injury, it is important to determine an approximate B deficiency threshold and to determine the effects of sub-optimal temperatures on growth and B uptake. In an experiment to determine tissue concentrations of B associated with B deficiency symptoms, transplants grown at a day/night temperature regime of 26/22°C exhibited B deficiency symptoms at 10–20 µg B g−1 dry matter. These tissue levels resulted from solution concentrations of 0.19–1.9 µM B (.002–.205 mg L−1 B). Root and shoot growth of flue-cured cultivars was near maximum at a 26/26°C day/night temperature regime. Burley cultivars were adapted to a wider temperature range for optimum growth compared to flue-cured cultivars. The B deficiency threshold decreased with decreasing temperatures and with increased day/night temperature differentials. Sub-optimal temperatures appeared to be the primary growth limiting factor for tobacco transplants in the float system with low B availability. Boron deficiency was a secondary factor in limiting growth.