Photosynthetic responses of cassava cultivars (Manihot esculenta Crantz) from different habitats to temperature.

Maximum photosynthetic CO2 exchange rates (Pn) of single attached leaves were determined for several cassava cultivars selected from different habitats and grown in pots outdoors at CIAT, Colombia, S.A. Pn rates were in a narrow range of 22 to 26 μmol CO2 m(-2)s(-1) for all cultivars tested when measured at high photon flux density, normal air, optimum temperature and with low leaf-air vapor pressure differences. For all tested cultivars (9 cvs.), there was a broad optimum temperature for Pn between 25 to 35°C. At temperatures below and above this range Pn declined in all cultivars with Pn rates reaching 80% of maximum at 20 and 40°C. Pn temperature coefficient (Q10) from 15-25°C was 1.6±0.2 across cultivars. No consistent relation existed between Pn, optimum temperature, and the original habitat.