Regional, Annual, and Individual Variations in the Dihydroxyacetone Content of the Nectar of Ma̅nuka (Leptospermum scoparium) in New Zealand

A method was designed and validated for the analysis of dihydroxyacetone in the floral nectar of ma̅nuka (Leptospermum scoparium). The method was applied to samples collected from different regions of the North Island and the Nelson region of the upper South Island of New Zealand during the period 2009–2012 as well as to nectar samples from some Australian Leptospermum species. The ratio of dihydroxyacetone to total sugar (DHA/Tsugar) was classified as low (<0.001 mg/mg), moderate (0.001–0.002 mg/mg), or high (>0.002 mg/mg). Inter- and intraregional variation were observed as well as interannual variation with variation from low to high classification occurring within one region and from low to moderate between years. Australian species also demonstrated elevated levels of dihydroxyacetone in the nectar. Some garden cultivars were shown to produce very high nectar DHA/Tsugar, and a survey of cultivars was undertaken; cultivars with single-flowered red or pink flowers were the most common producers of very high nectar DHA/Tsugar.