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Photosynthetic Selection of Zea mays L. I. Plant Age and Leaf Position Effects and a Relationship Between Leaf and Canopy Rates¹

Leaf apparent photosynthetic (Pn) rates of inbred, hybrid, and open pollinated plants were studied in association with a continuing program of photosynthetic selection and improvement of Zea mays L. Of major interest was the influence of plant age and leaf position on Pn rates and on results of Pn selection. Apparent photosynthetic rates of multiplant canopies (Pc) of hybrid strain combinations of NY821 and C153 were also measured to determine if variation of Pn rates was indicative of variation of Pc rates.

ANOVA revealed highly significant variation of Pn rates among pretassel, silk, and dough stages of inbred and open pollinated plants and among stages ranging from silk to late dent for hybrids. Pn rates generally declined as plants aged, but a small increase from dough to early dent was observed for two maize hybrids.

Variation of Pn rates among lower, middle, and upper leaf positions was highly significant for three hybrids, but was rarely significant for the inbred and open pollinated plants. Pn rates of the three hybrids were substantially higher at upper positions from blister through early dent. A significant statistical interaction of age and position effects on the hybrid Pn rates alluded to a more marked age effected decline of Pn at upper positions.

A simple comparison of mean Pn rates indicated that Pn response to plant aging and leaf position differed among maize genotypes. The differential response was potentially detrimental to Pn selection efforts.

The similarity of trends of mean Pn and Pc rates and a highly significant regression relationship between Pn and Pc rates over time and between two hybrids provided evidence that variation of Pn rates was indicative of variation of Pc rates.

Key Words: Inbred • Hybrid • Leaf area • Light response • Genotype • Variation • Corn

² Assistant professor, Dep. of Soil and Crop Sciences, Texas A&M Univ.; plant breeder, Dep. of Biological Sciences, Univ. of the West Indies; and professor, Dep. of Agronomy, Cornell Univ., Ithaca, NY 14853.

Received for publication August 14, 1976.