Evaluation of Rubber Tree Crown Clones for Yield and Magnesium Use Efficiency in a Xanthic Ferralsol

Abstract

The cultivation of rubber trees in the humid tropical Amazon region is only possible with the use of crown grafts with species of Hevea sp. that are resistant to South American leaf blight – (SALB) [Microcyclus ulei (P. Henn.) v. Arx.]. However, it has been observed that plants with grafted crowns are not efficient in remobilizing magnesium from the crown to the latex. The experimental design was a randomized block, with three replicates. Five crown clones were studied (CPAA C 01, CPAA C 06, CPAA C 18, CPAA C 45, and CBA 2) with two magnesium (Mg) levels [source: magnesium sulfate(MgSO4): low-Mg (150 g plant−1 of MgSO4 × 7H2O] and high-Mg (450 g plant−1 of MgSO4 × 7H2O). The panel clone used for tapping was CNS AM 7905 (Hevea brasiliensis). The results showed that the Mg levels influenced the crown clones differently in relation to yield, efficiency index and leaf and soil Mg concentration. Clone CPAA C 01 with a high-Mg produced over 2.0 t ha−1 of dry rubber. Clones CPAA C 01 and CPAA C 45 were the most efficient, while clone CPAA C 06 showed moderate efficiency and clones CPAA C 18 and CBA 2 were inefficient in using Mg. The Mg concentration in the latex was not influenced by the two Mg levels, with the only differences being between the crown clones.