The effect of boron levels in nutrient solutions on fruit production and quality of greenhouse tomatoes
Insufficient fruit set of tomatoes owing to poor pollination in low cost greenhouses is a problem in South Africa, as bumblebee pollinators may not be imported. Since sub-optimum boron (B) levels may also contribute to fruit set problems, this aspect was investigated. Greenhouse tomatoes were planted in acid-washed river sand. Four nutrient solutions with only B at different levels (0.02; 0.16; 0.32 and 0.64 mg l-1) were used. Leaf analyses indicated that the uptake of Ca, Mg, Na, Zn and B increased with higher B levels. At the low B level, leaves were brittle and appeared pale-green and very high flower abscission percentages were found. Fruit lacked firmness at the low B level and this problem worsened during storage. At the 0.16 mg kg-1 B-level, fruit set, fruit development, colour, total soluble solids, firmness and shelf life seemed to be close to optimum. The highest B-level had no detrimental effect on any of the yield and quality related parameters. However, using 'Solubor' as a source of B, high levels decreased soluble Mn concentrations in nutrient solutions, probably owing to the precipitation of insoluble MnO2. This was reflected in reduced leaf-Mn concentrations.