Ecotype variation in early growth, coppicing, and shoot architecture of tea tree (Melaleuca alternifolia)

Tea tree (Melaleuca alternifolia) is native to south eastern Australia where it is also grown as a coppice crop in plantations to produce an essential oil used in medicinal, agricultural and cleaning products. Recent studies of disease and drought resistance suggest that populations from the cooler, drier upland region of its natural range may be a source of novel abiotic and biotic stress tolerance, but studies of potted plants also indicate their growth is slower. In order to assess growth in the field and gain insight into shoot architecture attributes that may underlie productivity differences we established a broadly based germplasm collection (10 provenances; 94 seedlots and nominally 1880 trees) in a field trial at Lismore in northern NSW. Relative growth rates in the field were comparative with container grown plants with around a 12% height penalty in upland plants when favourable growth conditions were provided in the glasshouse and the field. Larger predicted penalties in biomass yield (about 42%) are expected, however, and were likely to be due to a sparser branching architecture in the seedling upland plants. Slower growth rates, and wider and thicker leaves with higher dry matter content, was consistent with earlier inferences that upland plants were arid adapted, and supported their recognition as a distinct ecotype. Faster regrowth following initial harvest of the seedling and early competitive coppice biomass yields, were also consistent with the prediction of a constitutively larger root system on arid-adapted upland plants.