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Physiological Basis of Successful Breeding Strategies for Maize Grain Yield

University of Guelph, Department of Plant Agriculture, Crop Science Bldg., Guelph, ON N1G 2W1, Canada

View larger version (17K): [in this window] [in a new window]   Figure 1. Average U.S. (1865–2005) and Canadian (1892–2005) maize yields in kilograms per hectare (15.5% moisture), 1866 to 1938 (pre-hybrid era; – US yields, – Canadian yields), 1939 to 2005 (hybrid era; – US yields, – Canadian yields). Data compiled by the USDA and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA).

View larger version (16K): [in this window] [in a new window]   Figure 2. Dissection of yield formation in maize into physiological component processes at the whole-crop level (adapted from Tollenaar and Lee, 2006).

View larger version (102K): [in this window] [in a new window]   Figure 3. (A and B) ERA hybrids from the 1930s and the 1990s, respectively, showing differences in leaf angle (Photo courtesy of D.N. Duvick). (C and D) Canadian hybrids at 9 weeks post-silking from the 1940s and 1980s, respectively, showing differences in visual stay-green. (E and F) Maize plants with excess source capacity, relative to sink capacity, which is typified by purpling of leaves and stalks. G. Maize plant with excess sink capacity, relative to source capacity, which is typified by premature senescence of the leaves and stalk. (H and I) Hybrids grown at a high plant population density showing symptoms of nitrogen deficiency and variability in ear size, respectively.

View larger version (32K): [in this window] [in a new window]   Figure 4. Pattern of dry matter accumulation throughout of growing season and distribution within a mature maize plant.

View larger version (21K): [in this window] [in a new window]   Figure 5. Leaf CO2 exchange rate (CER) of maize hybrids Pride 5, Pioneer 3902, and Cargill 1877 from tassel emergence to 6 wk after silking. Data shown are measurements taken at 1200 h on the day following the night of cold exposure. Vertical bars are standard errors of the mean. (Adapted from Ying et al., 2000.)

View larger version (17K): [in this window] [in a new window]   Figure 6. A schematic representation of the relationship between kernel number per plant and plant growth rate during the period bracketing silking (PGRS) for a hybrid (solid black line), Inbred line 1 (dashed line) and Inbred line 2 (solid gray line), showing differences in PGRS threshold for kernel set (T), initial slope of the relationship between kernel number and PGRS (S), and asymptote or potential kernel number per plant (A). (Adapted from Echarte and Tollenaar, 2006; Tollenaar and Lee, 2006).

View larger version (16K): [in this window] [in a new window]   Figure 7. Overview of a modern maize breeding program.

View larger version (19K): [in this window] [in a new window]   Figure 8. Northern Corn Belt Dent heterotic patterns. (Based on Troyer, 1999; Mikel and Dudley, 2006.)

View larger version (17K): [in this window] [in a new window]   Figure 9. Typical inbred line development scheme depicting a two-parent breeding cross involving two inbred lines from the Stiff Stalk heterotic pattern.