Screening for Photosynthetic Efficiency1

Maize ( Zea mays L.), sorghum ( Sorghum vulgare L.) and several other plants have maximum rates of photosynthesis of 50 to 60 mg CO 2 dm −2 hr −1 and have CO 2 compensation concentrations (Γ) near 0 ppm. In contrast, small grains and many other plants have maximum rates of photosynthesis of 20 to 30 mg CO 2 dm −2 hr −1 and Γ values near 60 ppm. By growing a mixture of these high and low Γ plants together in a closed chamber, a CO 2 concentration below that necessary for survival of the high Γ plants was obtained. Only low Γ plants remained alive after 5 to 8 days in the chamber. This is a rapid and simple method for screening populations of plants for high photosynthetic rates.