COULD FULL SUN EXPOSURE REPRESENT PHYSIOLOGICAL ADVANTAGES FOR CRIOLLO COCOA CULTIVATION?

Abstract

In Venezuela, the physiological performance of adult cocoa trees under full sun exposure is unknown. The long-term effect of high photon flux density (PFD) on leaf water potential (), leaf area index (LAI), gas exchange, photochemical activity of PSII, and photosynthetic pigment content in adult cocoa trees of Ocumare 61 (OC-61) was evaluated, in order to know if OC-61 could have a good photosynthetic performance in plants grown in full sun (E) or if on the contrary there is a physiological disadvantage compared to those grown in shade (S), self-shaded leaves were also evaluated in each condition (E+A and S+A). The OC-61 clone grown in E showed significant changes in some physiological traits: lower , lower IAF, higher rates of photosynthesis (A) and water use efficiency (WUE), lower intercellular CO2 concentration (Ci) and lower total chlorophyll, and carotenoid content. An increase in electron transport rate, PSII quantum efficiency, photochemical and non-photochemical extinction coefficient was found that would partially explain the higher A's in E; there was no decrease in maximum quantum efficiency indicating the absence of photoinhibition. Clone OC-61 is a shade tolerant crop; however, the results indicate that it can be acclimatized to high sun exposure without damage to PSII functioning, which could represent a physiological advantage for clone OC-61 grown in the study area.