Simulation of inflorescence dynamics in oil palm and estimation of environment-sensitive phenological phases: a model based analysis

For oil palm, yield variation is in large part due to variation in the number of harvested bunches. Each successively-producedphytomercarriesafemale(productive),maleorabortedinflorescence.Sincephytomerdevelopment takes3-4yearsandnearlytwophytomersareproducedpermonth,manyinflorescencesdevelopinparallelbuthavedifferent phenological stages. Environment-dependent developmental rate, sex and abortion probability determine bunch productivity, which, in turn, affects other phytomers via source-sink relationships. Water deficit, solar radiation, temperature and day length are considered key external factors driving variation. Their impact is difficult to predict because of system complexity. To address this question we built a simple model (ECOPALM) to simulate the variation in number of harvested bunches. In this model, trophic competition among organs, expressed through a plant-scale index (Ic), drives sex determination and inflorescence abortion during specific sensitive phases at phytomer level. As a supplemental hypothesis, we propose that flowering is affected by photoperiod at phytomer level during a sensitive phase, thus, contributing to seasonal production peaks. The model was used to determine by parameter optimisation the influence of Ic anddaylengthoninflorescencedevelopmentandthestagesatwhichinflorescencesaresensitivetothesesignals.Parameters wereestimatedagainstobservationofnumberofharvestedbunchesinIvoryCoastusingageneticalgorithm.Themodelwas then validated with field observations in Benin and Indonesia. The sensitive phases determined by parameter optimisation agreed with independent experimental evidence, and variation of Ic explained both sex and abortion patterns. Sex determination seemed to coincide with floret meristem individualisation and occurred 29-32 months before bunch harvest. The main abortion stage occurred 10 months before harvest - at the beginning of rapid growth of the inflorescence. Simulation results suggest involvement of photoperiod in the determination of bunch growth dynamics. This study demonstrates that simple modelling approaches can help extracting ecophysiological information from simple field observations on complex systems.