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INTRODUCTION
The cocoa tree (Theobroma cacao) is cultivated in the humid tropics for its seed (bean), the vast majority of which is used in the food industry for the production of chocolate and powder (for drinking, baking and ice cream manufacture). A small proportion is also sold as cocoa butter, which is used in the pharmaceutical and cosmetic industries. Cocoa is of international importance as a smallholder crop (5-6 million farmers) with only about 5% (our best estimate) of the world crop (annual total = 3.6 million t) produced on plantations. Historically, most cocoa was planted in newly thinned forest with little investment of monetary capital during the establishment or maintenance phases (Ruf, 1995). Nowadays, little forest remains in the traditional growing areas and its conversion to cocoa is not acceptable. Replanting former cocoa land is costlier and, as it is usually lower yielding, it is less profitable. In West Africa, where cocoa is usually grown under shade, there are long-standing problems over the tenure of the cocoa trees and shared cropping is widespread. As an internationally traded commodity, cocoa contributes to the livelihoods of an estimated 40-50 million people (World Cocoa Foundation, 2010).
A great deal of research has been reported on the ecophysiology and water relations of cocoa and this paper attempts to synthesize this research from an independent perspective and to do this in practically useful ways. It follows the format used in previous reviews in this series notably on coffee (Carr, 2001), banana (Carr, 2009), tea (2010a; 2010b), sugar cane (Carr and Knox, 2011) and coconut (Carr, 2011). It begins with a summary of the origin and centres of production of cocoa and the stages of crop development (including roots) in relation to water availability, followed by reviews of plant water relations, crop water use and water productivity. Various aspects of this topic have previously been reviewed (e.g. Alvim, 1977; Balasimha, 1999; Fordham, 1972) including, most recently, a paper by Almeida and Valle (2007) with a focus on factors influencing the growth and development of the cocoa tree. Emphasis here is placed on those publications describing research which has international relevance.
CENTRES OF PRODUCTION
The centre of diversity of cocoa is believed to...