Photosynthesis of wheat in a warm, irrigated environment -: II.: Traits associated with genetic gains in yield

Net photosynthetic rate (A(n)), stomatal conductance (g(s)), intercellular CO2 concentration (C-i), and chlorophyll concentration estimate ([Chl]) were measured on flag leaves of 30 random individual F-5 plants within each of eight F-2-derived bulks, from a cross between two spring wheat (Triticum aestivum L.) cultivars, Seri-M82, and Siete Cerros-T66 contrasting in A(n), and realized grain yield. Measurements were made on fully irradiated leaves of field plots growing in a warm, low relative humidity, irrigated environment. Average A(n) of F-2-derived families measured during grain filling ranged from 19.1 to 24.4 mu mol m(-2) s(-1) among families, with standard errors ranging from 0.35 to 0.53. Based on measurements of A(n) of flag leaf lamina of individual plants, measured several times during grain filling, four plants from each of four bulks were selected for high and low A(n) to represent the range of genetic diversity within and among F-2:5 families. From each of these 16 selected F-5 plants, head rows were grown to generate inbred F-5:7 lines for replicated yield trials, which were sown in two environments in the same locality, differing by five weeks in sowing date, and having mean grain yields of approximately 3.5 t ha(-1). Mean A(n) measured on randomly selected flag leaves of the inbred lines ranged from 16.3 to 24.6 mu mol m(-2) s(-1) over both sowing dates. A(n), g(s), and C-i all correlated with yield of inbred lines. Furthermore, A(n) and g(s) measured on individual F-5 plants correlated genetically and phenotypically with A(n), g(s), and yield of the inbred lines deriving from the same plants, in both environments where yield was evaluated. (C) 2000 Elsevier Science B.V. All rights reserved.