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

Maize ear fasciationKnowledge 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 MethodsUsing 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 DiscussionEar 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.ConclusionsPortuguese 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.玉米果穗簇生症 解析调控玉米果穗花序的基因，可为籽粒产量预测模型的优化提供理论支撑。玉米果穗簇生症表现为果穗异常扁化、穗行数显著增多，是葡萄牙玉米地方品种中广泛存在的数量性状。 材料与方法 本研究以果穗簇生性状存在极端差异的杂交组合衍生的分离群体（含149个F2:3家系）为材料，采用完全随机区组设计，在两点开展田间试验。测定了多个与果穗簇生相关的性状及产量的相关性与遗传力，鉴定了调控这些性状遗传的数量性状位点（Quantitative Trait Loci, QTL），并提出了对应位点的候选基因。 结果与讨论 果穗簇生症的广义遗传力为0.73。该性状与部分果穗直径、穗轴直径及穗行数性状间存在极显著相关性。针对23个产量及果穗簇生相关性状，共鉴定到65个QTL，其中11个在两个试验环境中均被检测到；针对3个主成分，每个环境可检测到5~6个QTL。所检测到的QTL分布于17个基因组区域，单个QTL可解释8.7%~22.4%的性状或主成分表型变异。本研究为这些QTL区域提出了多个候选基因，例如裸须基因1 (bearded-ear1)、分支无花丝基因1 (branched silkless1)、紧凑株型基因1 (compact plant1)、穗分枝基因2 (ramosa2)、穗分枝基因3 (ramosa3)、雄穗转雌基因4 (tasselseed4)及顶端穗基因1 (terminal ear1)。但仍有大量QTL定位到无已知候选基因的基因组区域，表明尚有部分染色体区域未被用于玉米果穗性状的遗传改良选择。 结论 葡萄牙玉米种质资源是开展玉米产量遗传改良以及解析果穗簇生性状遗传基础的宝贵基因或等位变异来源。未来研究应聚焦于对已鉴定基因组区域开展精细定位，以实现图位克隆。