Manganese Toxicity Induces Abnormal Shoot Growth in 'O'Neal' Blueberry

Manganese (Mn) is an essential micronutrient for plant growth, acting as a cofactor in enzymes and playing an important role in numerous oxidation-reduction processes. In Chile, high levels of foliar Mn have been reported in many fields of 'O'Neal' blueberry and are often associated with abnormal shoot growth in the crop. Abnormalities include multiple flushes of growth over the season, multi-laterals arising from a single position on the shoots (often called 'broom wish'), and small, crinkled leaves with reddish color in the margins. A study was done to determine the relationship between these symptoms and leaf and soil Mn in a 2 year-old field of 'O'Neal' blueberry. We suspected that high levels of Mn were affecting normal auxin and Ca metabolism in the plants and hypothesized that problems were probably due to 1) low soil pH induced by large amounts of sulfur applied prior to planting, 2) high amounts of Mn in the organic mulches (pine sawdust, manure, and pine needles) used, and 3) sensitivity of the cultivar to Mn. As expected, leaf Mn was correlated with abnormal shoot growth, ranging from 223 mg kg(-1) in plants with no symptoms to 476 mg kg(-1) in plants with severe symptoms. Symptoms were also related to Mn in sawdust and manure amendments but not to soil Mn. Thus, results indicate that organic amendments should be tested for high Mn and avoided in 'O'Neal' blueberry when levels are >350 ppm.