Eco-physiological responses of cocoa plants under shade and heat stress in Southeastern Ghana

Authors: Eric Opoku Mensah*, University of Ghana, Anders Rabild, University of Copenhagen, Denmark, Philippe Vaast, ICRAF, Richard Asare, International Institute of Tropical Agriculture (IITA), Christiana A. Amoatey, University of Ghana, Kwadwo Owusu, University of Ghana
Topics: Agricultural Geography, Biogeography, Environmental Science
Keywords: cocoa, heat, shade, photosystem II, stomatal density, rate of photosynthesis
Session Type: Virtual Paper
Day: 4/8/2021
Start / End Time: 6:25 AM / 7:40 AM
Room: Virtual 14
Presentation File: No File Uploaded

Heat stress is believed to have strong effects on the growth of cocoa plants especially affecting photosystem II efficiency, rate of photosynthesis and stomatal responses. Shade has been recommended as one of the solutions to buffer the effects of heat on cocoa production. However, full sun systems have been suggested to outweigh shading systems in terms of yield when nutrients and water are non-limiting. A trial was established using small experimental plots with potted seedlings in a two-factor randomized complete block design (RCBD) to help understand the effects of heat and shade on the eco-physiological functions of cocoa. Six-month-old seedlings from the Clone 67, obtained from the Cocoa Research Institute of Ghana (CRIG), were used for the trial. The treatments included heat stress with ambient temperature raised above 5° C using infra-red heaters and 60 % shade provided by black shade nets. Results revealed higher stomata and leaf mass per unit area from plants under stress. Higher predawn chlorophyll fluorescence recorded in the shaded plants indicated higher photosystem II efficiency and therefore better leaf functions of plants under shade. Stressed plants had photosynthetic rates between 3 - 4 mmol m-2s-1 lower than the controls. Photosynthesis was optimum at 500 mmol-2s-1 of photosynthetically active radiation (PAR) for the full-sun plants with the shaded treatments saturating around 400 – 450 mmol-2s-1 PAR. Shade has a positive effect on cocoa seedlings and can help protect the plants in areas of high temperatures to improve survival rates and establishment in the field.

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