Environmental and genetic influences on growth, flowering, and nectar production in mānuka (Leptospermum scoparium J.R. Forst. & G. Forst.) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand

Abstract

Dihydroxyacetone (DHA) in floral nectar of the Mānuka shrub, Leptospermum scoparium (J.R. & G. Forst.) is a direct precursor to methylglyoxal (MGO) the bioactive compound of manuka honey. Accumulation of DHA in Mānuka nectars varies between trees, localities, and years. However, the reasons for this variability are largely unknown and its origins in nectar are unclear. Since high DHA to total sugar ratios (DHA/TSugar) in fresh honey result in high MGO in mature honey, it follows that nectars with high DHA/TSugar will produce high-value honey indicated by a high Unique Mānuka Factor (UMF®) attracting premium returns for the NZ honey industry and NZ economy. It is key to further optimise both nectar and DHA production by selecting for high producers. Selecting/developing varieties for maximum nectar potential (NP) needs an understanding of the relative influences of genotype (G), environment (E), and their interactions (GEI) on relevant trait expression. The responses of genetic clones from three high yielding Mānuka lines expressing varying levels of nectar DHA to temperature, light, and soil moisture were studied in controlled environments. The relative performances of the clones were evaluated and contributions of G, E, and GEI to aspects of their growth, flowering and nectar production quantified.--Shortened abstract