Measurement of photosynthetic performance in crop plants under South African climatic conditions


Courtesy of PP Systems

A key objective of the research conducted by Dr Riekert van Heerden ( at North-West University, Potchefstroom, South Africa and Drs Kobie de Ronde (and team members) and Joseph Asiwe at the Agricultural Research Council (ARC–Vegetable and Ornamental Plant Institute & ARC–Grain Crop Institute) is to increase the production of crops important for the livelihoods of South African people. Drought is one of the most difficult challenges faced by resource-poor farmers and agriculture in general in South Africa. The sustainability and predictability of crop production in South Africa is severely restricted by drought. Moreover, it is predicted that sub-Saharan Africa is heading for a period of even more prolonged drought, which researchers warn could be among the most severe in decades. The need for crop plants with enhanced tolerance to water deficits is thus real and urgent. The current research is designed to identify sweet potato and cowpea genotypes with enhanced drought tolerance for immediate use in drier areas of South Africa as well as for breeding programmes aimed at developing more drought tolerant genotypes.

Since carbon metabolism plays such an important role in plant growth and productivity a key objective of their research is to assess the effects of drought stress on photosynthesis in selected cowpea and sweet potato genotypes. For these field experiments portable and highly reliable equipment, which can operate for extended periods of time under often extremely hot and dusty South African conditions, is an absolute necessity. Dr van Heerden uses the CIRAS-2 portable differential CO2/H2O IRGA for these experiments and finds the instrument ideally suited for his research. The superior portability and stability of the CIRAS-2 under these harsh climatic conditions deserves special mention. The CIRAS-2 is used in combination with a cuvette featuring precise and simultaneous control of light intensity, relative humidity and CO2 concentration (Fig. 1). Experiments have revealed large genotypic variation in photosynthetic response in these two crops under drought/dry-land conditions. Selected results obtained in some of these experiments are shown in Figs. 2 and 3.

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