THE EFFECT OF IRRADIANCE LEVEL ON COCOA (THEOBROMA-CACAO L) .1. GROWTH AND LEAF ADAPTATIONS

Improved tolerance of cocoa to full sunlight has the potential of incr easing yields while reducing the need for shade management. The effect s of irradiance on growth and leaf adaptations in plants grown from se eds or cuttings and subjected to full sunlight (1800 mu mol m(-2) s(-1 )) or shaded conditions (900 mu mol m(-2) s(-1)) were investigated. Le af size, internode length, total leaf area, and dry matter per plant w ere significantly reduced while leaf thickness, specific leaf weight, stomatal density, and leaf number per plant were increased in full sun light. The leaf area ratio, net assimilation rate, and relative growth rate were also reduced under full sunlight, although some genotypes, especially TSH 919, TSH 1188, and their progenies, seemed to grow bett er in full sunlight than in shade. The results suggest that some leaf adaptations may influence tolerance to high irradiance.