Analysis of differences in field performance of vegetatively and seed-propagated <i>Eucalyptus</i> varieties II: vertical uprooting resistance

Abstract

The aim of this study was to establish whether roots of micropropagated Eucalyptus grandis × E. nitens differ in their vertical uprooting resistance and architecture when compared with those of macropropagated E. grandis × E. nitens and seed-propagated E. grandis and E. nitens. Uprooting resistance was significantly lower for micropropagated plants than in other plant types after 16 months of field growth. All vegetatively propagated plants produced few and thick I-beam shaped roots, compared with the thin and numerous T-beam shaped roots of seed-propagated plants. Thinner T-beam shaped lateral roots evenly distributed around the stem enhanced resistance to vertical extraction more efficiently than thicker and fewer I-beam shaped roots. Some of the uprooted macropropagated E. grandis × E. nitens trees had produced the equivalent of a taproot (i.e. tap-sinker), compared with none of the micropropagated trees. Vegetatively propagated plants without tap-sinkers showed little resistance during vertical extraction, and their roots were generally asymmetrical and established just below the soil surface. Although the best predictor of uprooting resistance was a combination of the number of roots and root cross-sectional area at the root–stem junction, the number of roots was the most significant predictor. Micropropagation yielded an inferior root system than macropropagation during the first 16 months of field growth. Therefore, trees propagated in vitro may be unsuitable for commercial planting across areas with strong winds.

Keywords: anchorage; cold-tolerant; macropropagation; micropropagation; root architecture

Southern Forests 2010, 72(1): 31–36