Budding from rejuvenated clones: A good compromise between micropropagation and conventional budding

Industrial cloning of the rubber tree is carried out by budding, as the cutting technique is prevented by the very rapid reduction in adventitious rhizogenesis ability during ageing. The juvenile budding or 'juvenile type" (JT) was invented by the Dutch at the West Java Experimental Station in 1930: the scion was taken from the stem of young seedlings. Several experiments between 1930 and 1950 revealed the added-value of that type of material compared to the "mature type" (MT) of the conventional budding, which is used even today throughout the rubber growing world. A Chinese team adapted that "invention" in 1985 to take advantage of the rejuvenation induced by somatic embryogenesis from anther cultures. The few plantlets obtained were used to produce GVPs (buddings from in vitro plantlets). At the beginning of the 1990s, based on those data, the GRAD team used different horticultural processes and somatic embryogenesis to improve propagation by microcuttings and to produce GVPs from mature selected clones. Field trials with statistical design were conducted as early as 1994 in Ivory Coast, then in Thailand and in Nigeria. That work confirmed the merits of the GVP for budding success, growth and natural rubber production. However, the development of this new varietal type requires agronomic validation, as the results available, though they tally, come from small-scale field trials. In addition, knowledge needs to be acquired on the conservation of juvenility in rejuvenated clone bud wood gardens (JBG). Diversification of selected clones rejuvenated by somatic embryogenesis is also necessary. (Résumé d'auteur