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Environmental Controls on the Growth and Yield of Okra. I. Effects of Temperature and CO₂ Enrichment at Cool Temperature¹

Growth and yield responses of okra (Abelmoschus esculentus (L.) Moench, cv. Clemson Spineless) to 6 different day/night temperature regimes and 3 CO₂ concentrations were studied in controlled environment chambers of the Duke University Phytotron. The objective of these experiments was to characterize the effects of temperature and CO₂ concentrations on vegetative growth and fruit yield of okra. The day/ night temperature regimes in the greenhouses at ambient light and CO₂ concentration (350 ppm) were: 17/11, 20/14, 23/17, 26/20, 29/23 and 32/26 C, and the CO₂ concentration in the growth chambers at 20/14 C were 450, 675, and 1,000 ppm.

In the experiments at ambient CO₂ concentration, no plants survived at temperatures below 26/20 C. The plants grown at 26/20 C and higher temperatures in the greenhouses grew to maturity and produced fruits. Under CO₂ enrichment in growth chambers, however, the plants survived to maturity at 20/14 C. Thus at the suboptimal temperature of 20/14 C, CO₂ enrichment compensated for the adverse effects of cool temperature on the growth of okra. The chamber grown plants at 20/14 C produced the maximumd ry weight in 1,000 ppm CO₂. The greenhouse grown plants under ambient CO₂ and light produced the greatest dry weight at 32/26 C.

The results demonstrate why okra is not a productive crop at mean temperature of 26/20 C or below in ambient CO₂ concentration. However, at increasing atmospheric CO₂ levels okra becomes much more vigorous and productive at low temperature and therefore may spread into cooler areas if the global atmospheric CO₂ concentration continues to increase.

Key Words: Environmental controls • CO₂ enrichment • Okra growth • Cool temperature

² Sr. res. scientist and professor of botany, Botany Dep., Duke Univ., Durham, NC, and research associate, 1890 Research Lab, South Carolina State College, Orangeburg, SC, respectively.

Received for publication February 13, 1981.