**1. Introduction**

The performance of a wheat cultivar, which is normally measured by its adaptability and yield potential under target environments, is dependent on genetic and environmental factors as well as the interaction between these factors. Timely flowering, that is the switch

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from the vegetative phase to the reproductive phase, and the duration of the life cycle fine‐tune a cultivar to the targeted environment [1, 2]. Flowering is essential for repro‐ ductive success and occurs when conditions are favorable to maximize pollination, seed development, seed dispersal, and subsequent germination [1]. Flowering success is dem‐ onstrated by the ability of the plant to efficiently use a range of available resources includ‐ ing water, nutrients, temperature, day length, radiant energy, and relevant endogenous signals to maximize its potential yield and to escape stressful conditions during growth and development [1, 3]. Consequently, there is a need to better understand the genetic control of flowering time in wheat. Understanding the genetic control of the components of the life cycle, although complex, will enable plant breeders to exploit associated genes, thus fine‐tune the growth and development of the crop to fulfill the demands of a specific environment and to increase yield [1, 4]. Discovering genes that control flowering time in wheat have been one of the key research goals for decades [1] and is increasingly gaining importance due to the impact of projected climate change [5]. As a result, many loci influ‐ encing flowering time has been successfully mapped and their effects determined [1, 4].

The duration of the life cycle of bread wheat is controlled by numerous genes, including those associated with seed germination, vegetative growth, flowering time, seed matu‐ ration, and seed dispersal [6]. These processes form the foundation of the reproductive strategy of flowering plants. The interaction between these genes and the environment defines the ultimate phenotype [7, 8]. Flowering time is an important component of the life cycle with a very wide and complex genetic control. Three groups of genes with major influence on flowering time of wheat include vernalization response genes, photoperiod response genes, and genes controlling the developmental rate (earliness *per se* (*eps*)) when vernalization and photoperiod response requirements have been met [1, 9, 10]. With the exception of *eps* genes, the environment plays a role in the expression of vernalization and photoperiod response genes and thus, to their contribution towards flowering time and growth of wheat [1, 11, 12]. Reviewing currently available genetic and genomic resources for flowering time and the progress made so far toward introgressing known genes in elite germplasm is vital to guide future research. This chapter, therefore, discusses the progress made in discovering genes involved and the impact of their extensive allelic variation on flowering time. Additionally, the potential benefits of tailoring the flowering time of wheat to improve yield in the wheat production industry are also discussed. Furthermore, the chapter discusses the benefits of introgressing genes for other complimentary traits such as semidwarf and preharvest sprouting resistance on promising or advanced wheat breed‐ ing lines.

### **2. The process of flowering in bread wheat**

The process of flowering involves multiple interactions between major genes (vernalization, photoperiod response, and *eps* genes) and endogenous factors such as the developmental stage and floral gene activities acting together to promote flower initiation [13]. Crucial to the process of floral initiation is the establishment and maintenance of meristems. A specified class of vernalization response genes called *Vrn‐1* series (*Vrn‐A1*, *Vrn‐B1*, and *Vrn‐D1*) is responsible for this task in wheat [14–16]. The process consists of pools of undifferentiated cells that could either give rise to lateral organs such as leaves, auxiliary shoots (including flowers), and internode tissue, or that could serve as a continuing supply of new meristem cells. As a result, the type of cells produced and their ultimate developmental fate as part of vegetative or reproductive structures determine whether flowering occurs [13]. To initiate flowering, the flowering response or signal must be transferred through florigen to apices and induces meristem identity genes involved in the initiation of flowering following the accumu‐ lation of a light signal (photoperiod response) on the leaves [17–19]. This process is mediated by both vernalization and photoperiod response genes [18, 20]. Future research should iden‐ tify the meristem identity genes controlling floral transition and inflorescence development in wheat and other cereal crops [21].

from the vegetative phase to the reproductive phase, and the duration of the life cycle fine‐tune a cultivar to the targeted environment [1, 2]. Flowering is essential for repro‐ ductive success and occurs when conditions are favorable to maximize pollination, seed development, seed dispersal, and subsequent germination [1]. Flowering success is dem‐ onstrated by the ability of the plant to efficiently use a range of available resources includ‐ ing water, nutrients, temperature, day length, radiant energy, and relevant endogenous signals to maximize its potential yield and to escape stressful conditions during growth and development [1, 3]. Consequently, there is a need to better understand the genetic control of flowering time in wheat. Understanding the genetic control of the components of the life cycle, although complex, will enable plant breeders to exploit associated genes, thus fine‐tune the growth and development of the crop to fulfill the demands of a specific environment and to increase yield [1, 4]. Discovering genes that control flowering time in wheat have been one of the key research goals for decades [1] and is increasingly gaining importance due to the impact of projected climate change [5]. As a result, many loci influ‐ encing flowering time has been successfully mapped and their effects determined [1, 4].

78 Wheat Improvement, Management and Utilization

The duration of the life cycle of bread wheat is controlled by numerous genes, including those associated with seed germination, vegetative growth, flowering time, seed matu‐ ration, and seed dispersal [6]. These processes form the foundation of the reproductive strategy of flowering plants. The interaction between these genes and the environment defines the ultimate phenotype [7, 8]. Flowering time is an important component of the life cycle with a very wide and complex genetic control. Three groups of genes with major influence on flowering time of wheat include vernalization response genes, photoperiod response genes, and genes controlling the developmental rate (earliness *per se* (*eps*)) when vernalization and photoperiod response requirements have been met [1, 9, 10]. With the exception of *eps* genes, the environment plays a role in the expression of vernalization and photoperiod response genes and thus, to their contribution towards flowering time and growth of wheat [1, 11, 12]. Reviewing currently available genetic and genomic resources for flowering time and the progress made so far toward introgressing known genes in elite germplasm is vital to guide future research. This chapter, therefore, discusses the progress made in discovering genes involved and the impact of their extensive allelic variation on flowering time. Additionally, the potential benefits of tailoring the flowering time of wheat to improve yield in the wheat production industry are also discussed. Furthermore, the chapter discusses the benefits of introgressing genes for other complimentary traits such as semidwarf and preharvest sprouting resistance on promising or advanced wheat breed‐

The process of flowering involves multiple interactions between major genes (vernalization, photoperiod response, and *eps* genes) and endogenous factors such as the developmental stage and floral gene activities acting together to promote flower initiation [13]. Crucial to the process of floral initiation is the establishment and maintenance of meristems. A specified

ing lines.

**2. The process of flowering in bread wheat**
