Metabolic partition between radial vegetative growth and rubber production of Hevea brasiliensis clones of different metabolic classes, bled at unstimulated d4 frequency in Côte d’Ivoire

Abstract

Rubber growing is one of the most important industrial crops in Ivory Coast. In order to achieve a good sustainable rubber crop of Hevea brasiliensis in Ivory Coast, the effect of bleeding at unstimulated d4 frequency on radial vegetative growth was evaluated with 16 clones of Hevea brasiliensis divided into three classes of vegetative growth and metabolic activity, planted in a completely randomized block pattern. Agronomic (vegetative growth and rubber production) and physiological (sucrose and inorganic phosphorus levels) parameters were assessed over nine years. The results obtained showed that bleeding in d4 had a significant impact on the mean annual increase in circumference of bleeding trees (3.04 cm.yr -1 ) relative to that of non-bleeding trees (5.29 cm.yr -1 ). The reduction in growth expressed as a percentage of the vegetative growth potential was estimated at 42.53%. Mean annual circumference increments of unbleeded trees of clones of active (MAC; 5.46 cm.yr -1 ) and moderate (MMC; 4.96 cm.yr -1 ) vegetative and metabolic growth classes are significantly greater than those of bleeding trees of clones of the same classes (3.00 and 2.80 cm.yr -1 ). On the other hand, the average annual increments of the slow vegetative and metabolic growing clones (SMC) are hardly affected by bleeding. The production and reduction in growth were 58.96 g.a -1 .s -1 , 45.06% for MAC, 56.2 g.a -1 .s -1 and 43.55% for SMC, and 39.83 g.a -1 .s -1 and 23.8% for SMC, respectively. A very highly significant polynomial relationship (R 2 = 1) between percent reduction in increment (%RedAcc), rubber production and P/Sac and Pi/Sac ratios was found. The percentage of vegetative growth potential below 50% is a sign that bleeding at the unstimulated d4 frequency is a good indicator for improving the productivity of rubber clones without damaging the physiological state.