Scaling up oil palm (Elaeis guineensis Jacq.) seedling production through modified dry heat scarification and embryo rescue.

Abstract

Germination of oil palm seeds is naturally very slow, low and unsynchronized due to severe dormancy. Considering that in practice the propagation of oil palm is accomplished mainly by seeds, slow, low and worse still, failure to germinate obviously has serious consequences at the agronomic and socioeconomic scales. The present consumption rate of palm oil in the food and the manufacturing industries coupled with its recent use in production of biodiesel, call for an increase in productivity for fear that demand does not outweigh supply at the global scale. To mitigate this deficit, the government of Cameroon in accord with local councils has been allocating extensive hectares of land to international and national companies in the South West, Littoral and Centre Regions to extablish oil palm plantations. The latter need improved seeds adapted to the local agroecological zone. Unfortunately, CEREPAH, ‗the major producer and distributor of improved oil palm seeds in Cameroon witnessed a constant decrease in annual germination capacity (GP) of ≈5 % per annum from 2009-2013. Hence demand for improved oil palm seeds became greater than CEREPAH can supply. In response, CEREPAH is envisaging new approaches to be used alongside the conventional dry heat scarification (DHT) to maximize supply of improved oil palm seeds. It is within this context that this study was conceived. The general objective was to to identify approaches that could ameliorate annual germination rate of improved oil palm seeds at the IRAD-CEREPAH, La Dibamba, in groundwork to satisfy the present and future huge demand. Four specific objectives were set to attain this goal, amongst which where: to determine the causes of low annual germination capacity (GP); to optimize the traditional DHT by incorporating some growth promoting chemicals (GPC); to evaluate acid and hot water scarifications as alternative methods of breaking dormancy and finally to assess production of oil palm plantlets via mature zygotic embryo rescue. To determine the cause of unsynchronized GP, some biometric parameters were studied. Position dependent effect of seeds and the influence of harvesting date on germination were carried out to determine the causes of general low GP. In the second approach, the effect of incorporating different concentrations of some growth promoting chemicals (GPC) to the traditional DHT was appraised. Regeneration potential of vitro plantlets via MZE rescue of the ten CEREPAH commercial oil palm cultivars was tested on 10 modified Murashige and Skoog culture media (CM1-10). As concerns the causes of variation in GP, the results showed the existence of significant variation in biometric parameters like length, weight, number of kernel/seeds, shellxxv thickness between the 10 tenera cultivars commercialised by CERPAH. Similarly, it was found that the basal seeds (Orange coloured fruits), significantly higher than apex seeds (deep red coloured fruits) in terms of number, scored a lower germination compared to apical seeds. The results also showed that the harvesting date of FFB destined for seed production significantly influences germination capacity positively. As concerns optimization of DHT, it was observed that, Gibberellic acid (GA3) and hydrogen peroxide (H2O2) incorporation to DHT improved germination capacity (GP) than DHT alone. Significant differences were noted between the GPC and the control for parameters like GP, mean length of incubation time (MLIT) and coefficient of velocity of germination (CVG). Generally incorporation of GA3 and H2O2 significantly improved GP while CN2H2 decreased GP even lower than the control. H2O2 recorded the least MLIT (30-36 days) while CN2H2 registered the longest (90-120 days) for all seed cultivars tested. H2O2 also scored the highest CVG compared to other treatments. No germination was observed when the seeds were subjected to acid and hot water scarifications without prior scarification by DHT. Embryo rescue revealed a positive response to in vitro germination in all the ten seed cultvars. Cv1, Cv5 and Cv9 scored the highest germination capacity (90 %) while the least of 14 % was recorded in Cv8. Most suitable culture medium (CM5) registered 72 % while the least germination (48 %) was observed in CM1 and CM8. Robust vitro plantlets with complete differentiation into a shoot and root bud axes occurred in CM2, CM5, CM7 and CM10. Among the three auxin types compared, rooting of vitro plants was highly significant when treated with IBA at 1.5 mg/L.