Field growth and rubber yield of Hevea brasiliensis (Muëll.-Arg.) from budded versus in vitro micropropagated plants from clone IRCA 18

A hevea microcutting procedure has been defined for the propagation of selected clones, involving an initial rejuvenation phase. Experimental production based on clone IRCA 18 was carried out in 1992 and culminated in the setting up of a field trial in 1993 to compare the agronomic performance of in vitro plantlets with that of conventional budding. The results were analysed from the acclimatization phase, where problems in the resumption of apex growth have resulted in very high mortality. After growing for eight years in the field, the in vitro plantlets had a significant 6% advantage in terms of trunk circumference 1 m from the ground. A relation was sought between initial in vitro plantlet development at the time of planting, and their subsequent growth in the field. One of the challenges of micropropagation was to overcome the handicap of cuttings, with the inadequate anchoring ability of neoformed root systems. In the trial described here, none of the trees was lost through uprooting; moreover, we showed in a parallel study that in vitro plantlets obtained by micropropagation had a similar root development process to that of plants obtained from seed, notably with a vigorous taproot structure. In the two first tapping years, the in vitro plantlets produced 20% higher yields (in kg of dry rubber per tree). These results will be commented on in relation to the initial hypotheses put forward regarding the merits of in vitro plantlets for rubber cultivation, and to application prospects.