Abstract

Understanding how and when crops cope with and respond to stress during reproductive development may be able to forecast total crop production under abrupt climate change. We studied the effect of complete defoliation under time-specific climate-related conditions on inflorescence sex differentiation in oil palm. A total of 162 pisifera oil palm trees were completely defoliated at the rate of three trees per month between July 2007 and December 2011. Complete defoliation significantly increased male inflorescence induction by 104% when compared with control without defoliation. Acute soil water deficit (SWD) of 16.8 mm between the 30th and 60th day after complete defoliation (DAD) had an additional positive effect on male inflorescence production. A regression analysis on 18 time-specific, climate-related research and two inflorescence-related variables resulted in high regression coefficients for the time period 30th to 60th DAD. This is an indication that oil palm responds to complete defoliation stress after a 30-day delaying period. Total soluble sugars measured at 45 DAD showed a depletion of 55% in the leaves and 21% in inflorescence of defoliated trees compared to control trees without defoliation. Preferential sex differentiation in oil palm towards maleness is an acclimation response to the depletion of total soluble sugar inflected by mechanical and soil water deficit stresses. These results shall permit the simulation of male inflorescence induction and yield forecasting in other geographical locations.

Key words: Fruit bunches, Male inflorescence induction, Mechanical stress, Sugar depletion, Sex differentiation, Stress responses