Industrial propagation by rooted cuttings of mature selected clones of hevea brasiliensis
The importance of Hevea brasiliensis (rubber tree) as a cash crop keeps increasing warranting the development of new and more efficient techniques than the bud-grafting traditionally used for mass producing superior planting material. In vitro production of rubber trees by somatic embryogenesis and the good field performance (fast growth, high yield) of the resulting emblings have been reported for years, but so far only on an experimental scale. In vitro mass production of self-rooted rubber clones by somatic embryogenesis or microcuttings is hindered by a lack of responsiveness of most of the selected genotypes and by prohibitive production costs. Given this situation, macro propagation by rooted cuttings following in vitro propagation of mature selected clones was attempted by the SoGB estate in Côte d'Ivoire as a possible alternative to in vitro techniques only. Two industrial mature clones, clone A (70yrs-old) and clone B (53yrs-old), were first rejuvenated in vitro by somatic embryogenesis then micropropagated in greater numbers by microcuttings. After acclimatization, these in vitro-rooted microcuttings were potted in individual containers to be managed intensively as stock plants to produce macro cuttings. After 3 weeks under suitable rooting conditions in the nursery, rooting rates of 74.6% (1203/1613) for clone A and 76.5% (198/259) for clone B macrocuttings were obtained. The cuttings produced vigorous and taproot-like adventitious roots. After successful acclimatization, all the rooted cuttings developed true-to-type and 4 months later reached a sufficient height of 25-30 cm to be field planted. In addition to higher field vigor and true-to-typeness, cutting- derived rubber tree clones can be produced more quickly, on less nursery space at lower cost and in easier working conditions than traditionally bud-grafted plants. Further investigations are underway for assessing at the field level the comparative advantages of rooted cuttings versus grafted clonal offspring with respect to traits of major economic importance such as latex yield.
Authors : Aurélien MASSON, Jean-Marc JULIEN, Luc BOEDT