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

Abstract Net photosynthetic rate ( A n ), stomatal conductance ( g s ), intercellular CO 2 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 μmol 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 μmol 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.