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Variability and Selection Advance for Photosynthesis in Iowa Stiff Stalk Synthetic Maize Population¹

Photosynthesis is a primary trait influencing yield potential, and it should be improved in a yield-potential selection program. Information concerning the genotypic variability and inheritance of photosynthetic efficiency in maize (Zea mays L.) must be obtained before a yield-potential selection program is initiated.

We used CO₂-exchange rate (CER) of sections from excised leaves to estimate photosynthetic efficiency of 64 random inbred fines of maize derived from Iowa Stiff Stalk Synthetic (BSSS). Our study was conducted for years at one location. Measurements of CER taken during vegetative growth (CER 1) and during grain filling (CER 2) were used to estimate genotypic variances and heritabilities and to calculate selection advances for these two stages of plant development. We also evaluated the possibility of using specific leaf weight and leaf thickness as index traits for CER selection.

Results showed that estimates of additive variance were 1.7 and 4.9 times larger than estimates of genotype x environment variance at CER 1 and CER 2, respectively. Narrow-sense heritabilities were 0.58 for CER l and 0.80 for CER 2, and realized heritability values were 0.72 (CER 1) and 0.66 (CER 2). A high genotypic correlation between CER at CER 1 and CER 2 indicated selection at either developmental stage would produce nearly identical results. Actual selection advances (15% selection intensity) represented increases of 14 and 22% above population means for CER 1 and CER 2, respectively. Our data suggested that measurement of two replications of four plants/plot grown in two environments would provide most efficient selection advance for inbreds. We concluded that selection for improved CER in BSSS would be possible and that selection must be for CER per se.

Key Words: Zea mays L. • CO₂ exchange rate • Heritability • Selection Advance • Specific leaf weight • Leaf thickness

² Research associate and associate professors, respectively. Agronomy Dep., Iowa State Univ., Ames.

Received for publication September 20, 1976.