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Seasonal Patterns and Genotypic Differences in Glucose-6-Phosphate Dehydrogenase Activity in a Diallel Cross of Corn¹

Glucose-6-phosphate dehydrogenase (G6PD) (E.C. 1.1.1.49) activity was assayed in a four-parent dlallel cross of corn (Zea mays L.) to determine the level of activity at various stages of development (seasonal patterns) and to look for differences in G6PD activity among inbreds and the F₁ progenies. The enzyme was extracted from leaf blades of field-grown corn every week in 1972 from 2 weeks after seedling emergence until 7 weeks after silking. In 1973, the enzyme was extracted and assayed at 2-week intervals between 8 and 14 weeks after emergence.

Seasonal patterns revealed that G6PD activity in leaves was relatively low in all genotypes during the first 7 weeks after seedling emergence, but activity increased sharply between 7 and 10 weeks in those genotypes with high levels of activity. Activity remained high until 12 weeks after emergence and then decreased rapidly.

When seasonal means for G6PD activity were compared, twofold differences in inbreds were observed. Significant genotypic differences were noted for G6PD activity both years at every sampling except at 5 weeks after emergence in 1972. In 1973, all 12 F₁ progenies were compared, but no significant reciprocal effects were found. General combining ability for G6PD activity was significant, indicating that the level of G6PD activity in inbreds was reflected in the F₁ progenies. Based on general combining ability in 1973 and the close relationship between midparent means and F₁ progenies in 1972, assaying G6PD activity in corn inbreds should be adequate to predict the levels of activity in F₁ progenies.

Key Words: Inbreds • F₁ progeny • Heterosis • Enzyme • Reciprocal effects • General combining ability • Specific combining ability • Leaf blades • Midparent means • Zea mays L.

² Associate Professor of Crop Physiology.

Received for publication May 9, 1973.