Influence of Propagation Method on Root Architecture and Other Traits of Young Citrus Rootstock Plants

Abstract

There are generally inadequate supplies of seed for the newest rootstocks to satisfy the growing demand for the propagation material to be used in commercial citrus nurseries. Consequently, rootstock propagation, which is traditionally by seed, now often makes use of alternative methods such as cuttings and tissue culture (TC). Propagation through cuttings and TC will generate a root system that is largely composed of adventitious or lateral roots, compared with seed propagation, which will generally promote the formation of a well-defined taproot. In this study, we compared root architecture and growth of seven different rootstock plants, generated from seed, stem cuttings, or TC, during the early weeks of growth in the greenhouse. Based on total dry biomass, root mass fraction of plants generated from cuttings ranged from 11% to 16%, and from 16% to 29% and 21% to 30% for micropropagated plants and seedlings, respectively. Plants propagated through cuttings had the most primary roots (7–10), followed by tissue culture–propagated plants which developed an average of 2–6 primary roots. As expected, plants grown from seeds mostly developed a single and well-defined taproot during the first weeks. The total number of first order lateral roots was highest in the plants propagated as cuttings (108–185) compared with 53–103 and 43–78 for tissue culture–propagated plants and seedlings, respectively. Similarly, specific root length (SRL) was highest in plants derived from cuttings (21–43 m·g−1) and lowest in plants grown from seed (7–20 m·g−1). It is suggested that the larger number and length of roots on rootstock plants propagated through vegetative methods may be better suited for resource acquisition as compared with seed propagated plants.