Photosynthesis of wheat in a warm, irrigated environment -: I:: Genetic diversity and crop productivity

Net photosynthetic rate (A(n)), stomatal conductance (g(s)), chlorophyll content and dark respiration rate were measured on 16 wheat cultivars (Triticum aestivum L.), grown in replicated yield trials in a warm, irrigated, and low relative humidity environment in central Mexico. Measurements were made on flag leaves in full sunlight at three different stages of plant development (booting, anthesis, and grain filling), and at different times of the day. Two experiments were conducted with sowing dates in December 1991 and March 1992, whose average daily temperature for their respective growing cycles were 21 and 25 degrees C. Physiological measurements were compared with agronomic performance on the same field plots. A(n) was fairly stable during the day between 10:00 and 14:00 h, and across experiments, despite differences in leaf temperature of up to 4 degrees C. A(n) fell noticeably at successively later stages of plant development, however, and there were clear differences among cultivars. With both sowing dates, A(n) and g(s) measured at all three stages of development correlated significantly with yield and biomass of the cultivars. A(n) during the grain filling period was also strongly associated with chlorophyll loss. The data indicate that differences in A(n) throughout the crop cycle as well as variation in the onset of senescence may be important variables affecting wheat yield potential in warm environments. (C) 2000 Elsevier Science B.V. All rights reserved.