Major determinants of fruit set and yield fluctuation in coconut (Cocos nucifera L.)

The final yield of coconut (Cocos nucifera L.) is determined by early fruit set. Thus understanding the factors controlling fruit set including climate change is of importance for assessing the yield and its accurate prediction. This study assessed the survival pattern of female flowers produced in different months of the year, the effects of climate factors during early phase of flowering and the competition for assimilates from previously formed fruits on the fruit set of newly opening inflorescences in a 25 26 year-old coconut plantation in the Intermediate Zone (IL1a) of Sri Lanka over a period of three years. The rate of fruit survival since the onset of flowering to maturity varied with the month of inflorescence opening. Abortion of fruits after three months from inflorescence opening was negligible. The optimum (Topt-In vitro) and maximum (Tmax-in vitro) temperatures for in vitro pollen germination were 28 degrees C and 39.7 degrees C, respectively. The fruit set of an inflorescence/s opened in a given month (number of set fruits palm(-1) month(-1)) was negatively correlated with the total reproductive dry matter requirement of the palm (TDMR) of the month of inflorescence/s opening (first month), and the number of high temperature days (T-max >= 33 degrees C) during the first three months of inflorescence opening, whilst it was positively correlated with the number of female flowers produced in the inflorescence. There was a highly significant correlation between the monthly fruit set (at three month stage) and the corresponding harvested fruit yield palm(-1) month(-1). The lag period between flowering (opening of the female phase) and fruit maturing was eleven months.