Relevant factors associated with crown expansion in oil palm (Elaeis guineensis Jacq.)

Summary Trends in crown expansion, the area of the youngest fully expanded leaf (LA) against age were studied in two oil palm progeny trials, and one density x fertilizer experiment, the latter comparing 110, 148, and 186 palms per ha each with four fertilizer levels. LA against age was best fitted by a logistic growth curve with maximum LA (L_m) and the time required to reach 0.95 L_m (t_0.95) as characteristic parameters. Progenies significantly differed in L_m and t_0.95. Increasing planting density significantly decreased L_m and t_0.95, while fertilizers increased L_m and t_0.95 only at the lowest density. Population means of the experiments markedly differed in L_m and t_0.95 values. Based on the, so called, Leaf Expansion Ratio (ER), being the ratio of LA at maximum expansion rate and LA at its final size, individual palms were selected for a rapid increase in LA, but a relatively low final size. The first characteristic means selection for rapid ground coverage, which resulted in palms with a higher Total Dry Matter Production (TDM) prior to canopy closure. The second characteristic appeared to lead to selection for high Bunch Index (the proportion of TDM used for fruit bunch production), indicating that L_m is a measure for the relative sink strength of leaves for assimilates. Selection for high ER values appeared feasible and this would increase yield during the economic life of a planting. The practical aspects of using ER values as a new selection criterion in oil palm breeding were discussed.