The Genetic Architecture of Maize Photoperiod Sensitivity as Revealed by Recombinant Inbred Line, Backcross, and Heterogeneous Inbred Family Populations.
No Thumbnail Available
Files
Date
2009-01-06
Authors
Journal Title
Series/Report No.
Journal ISSN
Volume Title
Publisher
Abstract
The genetic diversity of elite temperate maize germplasm is very narrow in comparison to the genetic diversity available across of the entire species. Tropical maize germplasm has frequently been cited as a potential source of enhanced genetic diversity that could be used to increase corn productivity. One obstacle to utilizing tropical maize germplasm in temperate breeding programs is photoperiod sensitivity, which is very common in tropical adapted maize lines. An investigation of the quantitative trait loci (QTL) contributing to maize photoperiod sensitivity may increase the facility and ability with which maize breeders can adapt tropical maize germplasm to temperate latitudes.
The inductive phase of maize photoperiod sensitivity was studied in a diverse set of temperate and tropical lines. From a factorial mating of two temperate and two tropical inbreds, four populations of recombinant inbred lines (RIL) were developed for the purpose of mapping the QTL underlying photoperiod sensitivity in tropical maize. Plants were grown in both long- and short-day environments and a number of traits were measured in each environment. These traits include flowering time, plant height, leaf number, and ear structure traits. The trait differences between long- and short-day environments were reported as the photoperiodic responses of the RILs. Utilizing the data of both individual and combined mapping populations, QTL were identified using Iterative QTL Mapping (iQTLm). The positions and effects of these QTL were compared between populations and with flowering time and plant height QTL from other mapping studies. We detected four regions in the genome that produced large photoperiod effects and named these ZmPR1, ZmPR2, ZmPR3, and ZmPR4. These four QTL accounted for 75% of the phenotypic diversity for photoperiod measured by our analysis. Similar QTL positions have been detected by other researchers studying photoperiod sensitivity and flowering time in maize. In addition to a major QTL on chromosome 3, QTL affecting the tasseled ear phenotype of maize were found in the ZmPR3 and ZmPR4 QTL regions, implicating these QTL as also having effects on floral morphology. The four ZmPR loci are the most promising as targets of marker-assisted selection against photoperiod sensitivity in maize.
Verification of the four ZmPR QTL was undertaken in four BC2F3:4 mapping populations. The B73 × CML254 had the same parentage as one of the RIL populations originally used to identify the ZmPR loci. We verified the presence of three of the four ZmPR loci in this population. We also found that the other three mapping populations, derived from crosses of B73 × Ki3, B73 × CML247, and B73 × Ki11 showed significant flowering time and plant height associations at some of the ZmPR loci. Winter nurseries were used to verify that the ZmPR4 QTL, which was the strongest photoperiodic flowering time QTL detected in previous mapping studies, was indeed a photoperiodic and not flowering time per se QTL. An F2 population of Ki14 × CML254 was used to identify allelism at the ZmPR loci. Only ZmPR4 and ZmPR2 showed allelism between these two tropical lines for flowering time and height traits, respectively.
The utility of QTL mapping for applied breeding programs is often limited by the transferability of QTL across populations and by the lack of precision in QTL mapping. One solution to these obstacles is to fine-map and clone the gene or genes underlying the QTL. We developed several heterogeneous inbred families (HIFs) from four RIL populations in order to facilitate fine-mapping. We observed several traits in these HIFs in phytotron, greenhouse, and field environments. We report the manner with which the HIFs were derived, as well as some observations and notes about future fine-mapping directions with these HIFs.
Description
Keywords
Mapping, Maize, QTL, Photoperiod, HIF, RIL, Backcross
Citation
Degree
PhD
Discipline
Crop Science
