Genetic analysis of ear development and tassel architecture in maize (Zea mays L. ssp. mays)

Yield potential of maize (Zea mays L.) has been increased significantly during the last century. Along with genetic gains for grain yield, changes in other traits have included an increase in the number of ears per plant (i.e. fewer barren plants) and a reduction in tassel size. The objectives of this study were 1) to identify Quantitative Trait Loci (QTL) associated with number of ears per plant (EPP), growing degree units to anthesis (GDU), plant height (PH) and tassel architectural traits, and 2) to evaluate the consistency of the QTL across environments. A population of 218 recombinant inbred lines (RILs) derived from two nearly isogenic inbreds, C103 and C103AP was evaluated for EPP, GDU, PH and four tassel architectural traits. The genetic map of 123 Simple Sequence Repeat (SSR) loci covered 894 cM. At least 5 novel regions for EPP were detected on chromosomes 2, 3, 6, 8 and 9. A region flanked by loci umc1858 and umc1309, on chromosome 8 (bins 8.04-8.05; a bin is an arbitrary subdivision of the maize genome based on a set of core markers) had a major influence on EPP, PH and GDU to anthesis. With respect to tassel morphology, a total of 32 QTL were identified for tassel branch number (TBN), tassel length (TL), central spike (CSL) and branching zone length (BZL). The majority of these QTL were located on chromosomes 1, 2, 3, 4 and 8. The QTL for TBN, TL and CSL with strong association to the phenotypic variance were located in bins 2.01, 2.06, 2.08 and 9.03. In these bins candidate genes and QTL have not been identified; therefore, this is the first report of a biological function with respect to tassel morphology for those regions in the genome. Comprehensive descriptions of the QTL related to the traits evaluated in this study are provided in the individual chapters of this dissertation. Many results found have not been described previously in the literature and will contribute to the current knowledge. Finally, further study of these regions is required for better understanding of the genetic factors affecting meristem initiation, maintenance and development in maize.