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Field Emergence Comparisons of Opaque-2 and Surgary-2 Opaque-2 Segregates in Two Maize Synthetics¹

The improved protein quality associated with opaque-2 (o2) maize (Zea mays L.) has not been widely used because grain yield, grain quality, and field stands generally are reduced relative to normal maize. This study was conducted to determine if the superior grain quality of sugary-2 opaque-2 (su2 02) would be expressed also in seedling emergence percentage, rate of emergence, and seedling weight by comparing 02 and su2 o2 segregates of S₁ and S₂ ears from two maize synthetics.

Very similar emergence responses were obtained [or the two endosperm classes when S₁ segregates were examined. The means for emergence percentage, rate of emergence, and seedling weight favored the o2 phenotype over the su2 o2 phenotype; however, significant differences were obtained only [or rate of emergence and seedling weight.

Under the cold field conditions encountered when S₂ segregates were examined, o2 kernels were significantly superior to su2 o2 in emergence percentage and rate of emergence. Opaque-2 kernels were larger, heavier, and had lower specific gravity than su2 o2 kernels. Relationships among traits within endosperm classes were different than [or the pooled endosperm classes, however. Percentages of seedling emergence within the o2 and su2 o2 classes were positively correlated with specific gravity of S₂ kernels and rate of emergence, but were negatively correlated with weight and size of kernels. The apparent contradiction reflects the negative relationship between seed size and specific gravity within both the 02 and su2 o2 classes. Heritability estimates for the emergence traits were large and suggest that selection for improved emergence should be effective within either of the endosperm classes. Seedling emergence of o2 was not improved by the superior kernel texture of su2 o2 contributed by the su2 gene.

Key Words: Kernel density • Heritability • Seedling emergence • Zea mays L.

² Research geneticist, AR, SEA. USDA, and professor of agronomy, Iowa State Univ.; and associate professor of statistics, Iowa State Univ.

Received for publication July 11, 1979.