Photosynthetic efficiency was measured by infrared analysis of net CO 2 exchange (NCE), using single attached leaves of intact greenhouse grown plants. The leaves were sampled as they approached full expansion or shortly thereafter. One or two measurements of the rate of NCE by primary or trifoliate leaves from several plants were used to estimate the photosynthetic efficiency of a variety. The mean from five observations, usually five different leaves, was used to estimate the genetically controlled potential in photosynthetic efficiency of individual plants from segregating progenies. ‘Michelite‐62’ significantly exceeded the closely related variety ‘Monroe’ by about 9% and ‘Perry Marrow,’ ‘Steuben,’ and 'Red Kidney' by 22%, 35%, and 31%, respectively. Light response curves for Michelite‐62 and Red Kidney were similar, but the net CO 2 uptake of Michelite‐62 exceeded that of Red Kidney by about 20% at all light intensities above the compensation point. Light saturations of about 37.7 and 70.0 kilolux, respectively, were obtained with winter and summer grown plants, but the absolute rate of net CO 2 uptake was about the same for the two intensities. Below the compensation point, Michelite‐62 evolved more CO 2 than Red Kidney. It was determined that the basis for the varietal difference in NCE resides in the reactions of photosynthesis that proceed in the dark rather than those that are light dependent. The photosynthetic efficiencies of Red Kidney and Michelite‐62, their F 1 and F 2 progenies, and a backcross to Red Kidney suggested that the genetic mechanism controlling the varietal difference in net CO 2 exchange rate is quantitative, that there may be relatively few genes involved, and that there is some dominance for the low photosynthetic efficiency of Red Kidney.
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Izhar et al. (1967) studied this question.