Photosynthetic and growth responses of Theobroma cacao L. clones to waterlogging

Six high yielding cacao clones (CCN-10, CP-49, CP-06, CEPEC-2007, CEPEC-2008, and PS-1319) were evaluated for photosynthetic performance, growth, and leaf nutrient concentration in response to 45 days of root waterlogging. Submergence reduced net CO2 assimilation (A). The highest A value (6.8 mmol CO2 m-2-s-1) was observed in the control plants of CCN-10 at 15 days after submergence, and CEPEC-2007 and PS-1319 30 at days of submergence. Stomatal conductances (gs) were 115 and 102 mmol H2O m-2-s-1 for CP-49 and CCN-10, respectively. Fifteen days of submergence increased the leaf intercellular (Ci) to atmospheric CO2 concentration (Ca) ratio (Ci/Ca) and decreased gs with CEPEC-2008 and PS-1319 being the most sensitive clones. CCN-10, CP-49, and CP-06 had relatively higher mean values of A and gs after waterlogging than other clones. All CEPEC-2008 and PS-1319 plants died after 35 days of waterlogging. The surviving clones had lower root, leaf and total plant dry weight, leaf area, leaf biomass ratio, relative growth rate, and leaf number, with the exception of clones CP-06 and CEPEC-2007. Waterlogging also decreased leaf concentrations of N, P, K, and Mg in all clones, except N in CEPEC-2007. The CCN-10 clone was the most tolerant to waterlogging with the least effects of waterlogging on leaf gas exchange. Clones CP-49, CP-06, and CEPEC-2007 showed intermediate tolerance, while CEPEC-2008 and PS-1319 were highly sensitive.