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Photosynthetic Rates of Six Maize Cultivars During Development

Agric. Canada, Land Resource Res. Centre, Bldg. 74, C.E.F., Ottawa, Ontario, Canada K1A OC6

C. J. Marur and R. I. Hamilton

IAPAR, CX Postal 1331-86100, Londrina, Parana, Brazil
Agric. Canada, Plant Research Centre, Bldg. 12, C.E.F., Ottawa, Ontario, Canada K1A OC6

^* Corresponding author.

Production estimates based on photosynthate accumulation are affected by changes in photosynthesis rates related to aging in different cultivars. The influence of leaf and plant age on photosynthetic rates was investigated in six maize (Zea mays L.) cultivars with maturity ratings ranging from <2300 to >3500 CHU (corn heat units). Photosynthesis and irradiance measurements were fitted to rectangular hyperbolas using a nonlinear fitting technique. These curves were analyzed as a function of cultivars, and leaf and plant age. For comparison among cultivars and age groups, photosynthesis was represented by P₂₀₀₀ (net photosynthetic rate at irradiance (I) = 2000 µmol m^2–2 s^–1. In all cultivars, early leaves had lower P₂₀₀₀ values at a given leaf age than late maturing leaves. The P₂₀₀₀ values tended to increase to a maximum at the time of full individual leaf expansion and then decrease. The duration of maximum P₂₀₀₀ values for leaves nearest the ear were longer than for earlier or later developing leaves. Leaves nearest the ear for early maturing cultivars tended to have lower P₂₀₀₀ values than later maturing cultivars at comparable leaf ages. Plant photosynthesis patterns were the same for all cultivars in relation to plant age and phenological development. Photosynthesis (P₂₀₀₀) was low for the six-leaf stage, reached a maximum just before tasselling, and then declined during brown silk, blister, and dent stages. A quadratic equation described the relationship between P₂₀₀₀ and plant age. The trend was for latermaturing cultivars to have significantly (P < 0.05) larger P₂₀₀₀ values than earlier-maturing cultivars at comparable phenological stages. Significant cultivar differences were found in leaf development rate and length of vegetative period (P < 0.10).

Received for publication May 5, 1988.

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