Quantitative Assessment of the Agro-physiological Advantages of Upward Tapping in Relation to the Downward Tapping of the GT 1 and PB 260 Rubber Clones [Hevea brasiliensis, Muell. arg. (Euphorbiaceae)] in Southwest Côte d'Ivoire

The downward tapping on virgin bark of the lower panel (BO) is immediately followed by the upward tapping on virgin bark of the upper panel (HO), consecutively. To determine the agro-physiological advantages of one tapping over another, a study of the downward and upward tapping of the GT 1 and PB 260 clones of Hevea brasiliensis was carried out in southwestern Côte d'Ivoire. For this purpose, the rubber trees were tapped in a downward half-spiral (S/2) at the opening for nine consecutive years, followed by upward quarter-spiral tapping (S/4U) for four consecutive years. The agronomic parameters (rubber production and vegetative growth), tapping panel dryness and the latex micro-diagnosis, were evaluated. For GT 1 clone, the transition from the downward tapping panels to the upward tapping panels resulted rubber productivity gain of 35%. Meanwhile for PB 260, rubber productivity gain was 37%. Regardless of the clone and tapping direction, the higher the rubber productivity of a respective tapping panel, the lower the isodiametric growth of the tree trunk was recorded. Latex harvesting systems, and clone’s combination, did not influence the tapping panel dryness or the physiological profile of the trees. Finally, it should be concluded that upward tapping is more productive than downward tapping, but the quantification of the gains in this rubber production depends on the clone.