Genetic Architecture of Ear Fasciation in Maize (Zea mays) under QTL Scrutiny

Abstract

Maize ear fasciation: Knowledge of the genes affecting maize ear inflorescence may lead to better grain yield modeling. Maize ear fasciation, defined as abnormal flattened ears with high kernel row number, is a quantitative trait widely present in Portuguese maize landraces.

Material and methods: Using a segregating population derived from an ear fasciation contrasting cross (consisting of 149 F2:3 families) we established a two location field trial using a complete randomized block design. Correlations and heritabilities for several ear fasciation-related traits and yield were determined. Quantitative Trait Loci (QTL) involved in the inheritance of those traits were identified and candidate genes for these QTL proposed.

Results and discussion: Ear fasciation broad-sense heritability was 0.73. Highly significant correlations were found between ear fasciation and some ear and cob diameters and row number traits. For the 23 yield and ear fasciation-related traits, 65 QTL were identified, out of which 11 were detected in both environments, while for the three principal components, five to six QTL were detected per environment. Detected QTL were distributed across 17 genomic regions and explained individually, 8.7% to 22.4% of the individual traits or principal components phenotypic variance. Several candidate genes for these QTL regions were proposed, such as bearded-ear1, branched silkless1, compact plant1, ramosa2, ramosa3, tasselseed4 and terminal ear1. However, many QTL mapped to regions without known candidate genes, indicating potential chromosomal regions not yet targeted for maize ear traits selection.

Conclusions: Portuguese maize germplasm represents a valuable source of genes or allelic variants for yield improvement and elucidation of the genetic basis of ear fasciation traits. Future studies should focus on fine mapping of the identified genomic regions with the aim of map-based cloning.

Fig 1. QTL detected for ear fasciation and related traits using 149 F_2:3 families (PB260 (non-fasciated) x PB266 (fasciated)) at two environments in Portugal (Coimbra and Montemor).

Bar positions indicate the locations of quantitative trait loci (QTL): outer and inner interval correspond to 1-LOD and 2-LOD support interval, and are indicated as full box and a single line respectively. QTL nomenclature was arranged by the trait name plus environment abbreviation (c = Coimbra and m = Montemor) and the order number of detected QTL for the same trait in the genome (the higher the n°, the lower the contribution of the detected QTL for the explained phenotypic variability).

Fig 2. Representation of the ear fasciation and related traits QTL regions per maize chromosome, with indication of respective detection environment.

For each chromosomal region, the respective candidate genes are indicated.