Genetic Diversity and Improvement of Contemporary Proprietary North American Dent Corn

Abstract

Coefficient of parentage (CP) is useful to estimate genetic diversity (1 − CP) among a set of lines. Estimated diversity among 846 proprietary inbred corn (Zea mays L.) lines registered in the United States from 1976 to 2005 shows favorable diversity of 0.944. Less diversity (0.859) was found among 47 widely grown hybrids from 1995 to 2001. Cluster analysis of the 55 parental inbreds formulating these 47 hybrids found nine family clusters, four that were Iowa Stiff Stalk Synthetic (BSSS) and five that were non‐BSSS, with intergroup diversity of 0.99 between BSSS and non‐BSSS. There was less genetic diversity among BSSS (0.64) than among non‐BSSS (0.90) inbreds. Genetic diversity within the nine family clusters B73/B14, B73/B37, B73/Maiz Amargo, B37/B14/Maiz Amargo, Miscellaneous/Oh43, Mo17/LH123, LH82, Oh07/Midland/Female Composite, and Iodent were 0.238, 0.285, 0.285, 0.735, 0.817, 0.525, 0.346, 0.554, and 0.539, respectively. Evaluation of the lineage of 470 recently (1996–2005) registered proprietary inbreds found that 170 (36%) are direct descendents of the public inbred B73. Breeding progress was estimated using progeny to parent side‐by‐side comparisons. Significant increases per breeding cycle were found for inbred grain yield (6%), plant height (2.3%), ear height (2.2%), and kernel weight (3%), but ear length decreased 4%. Hybrid grain yield increased 2.2% per breeding cycle. A positive correlation (0.36) was found between inbred and hybrid grain yields.