Rate of leaf expansion: A criterion for identifying oil palm ( Elaeis guineensis Jacq.) types suitable for planting at high densities

Abstract

The aim of the present study, carried out in South Sumatra under conditions of high solar radiation and a rainfall of about 2500 mm per year, was to identify oil palm material suitable for planting at high densities. To that end, we monitored leaf expansion of tenera progenies descending from the pisifera male parent origins Ekona, Nigeria and Calabar, by fitting logistic growth curves through the area of the fully developed youngest leaf as a function of palm age. In addition, estimates were made of the (asymptotic) maximum leaf area attained ( L max ) and the time to reach 95% of L max ( t 0.95). During the first 5 years after planting when the canopy closes, i.e., Phase 1 of canopy expansion, the area of individual leaves was very similar among the three origins, although the leaf area of the origin Nigeria slightly exceeded that of the two other ones. During the second 5-year period (Phase 2), leaf expansion rate started to divert: Calabar already reached t 0.95 at 6.9 years after planting compared with 7.4 years for Nigeria and 8.8 years for Ekona. During Phase 3, the final phase of stable leaf area, Calabar attained a lower L max (7.99 m 2) than the two other origins: 9.63 and 10.11 m 2 for Nigeria and Ekona, respectively. Logistic growth curves were also used to calculate leaf area index ( LAI). For maximum yield per ha the optimal LAI was assumed to lie between 5.5 and 6.0. When planted at a standard density of 143 palms per ha, compared with the density of 135 palms per ha used in this study, LAI at mature canopy size (Phase 3) would be 5.6 for Ekona; 5.4 for Nigeria; and 4.5 for Calabar. Because the LAI of Calabar is far below the optimal range, it was concluded that the planting density of Calabar can be increased to 160 palms per ha, which gives an LAI of 5.0 at Phase 3. General Combining Ability (GCA) values, i.e., the additive genotypic effects (of parents), for bunch yield as well as L max varied considerably among individual pisifera male parents. In particular, some pisifera of the origin Nigeria combined high GCA values for yield with low GCA values for L max . Such an inverse relationship offers the possibility to select pisifera male parents for producing tenera material suitable for planting at high densities. The study further concludes that L max is a more suitable criterion for estimating optimal density than the conventional method based on mean leaf area.