**Abstract**

Development of climate-resilient genotypes with high agronomic value through conventional breeding consumes longer time duration. Speed breeding strategy involves rapid generation advancement that results in faster release of superior varieties. In this approach, the experimental crop is grown in a controlled environment (growth chambers) with manipulation provisions for temperature, photoperiod, light intensity, and moisture. The generation of the crop cycle can be hastened by inducing changes in the physiological process such as photosynthesis rate, flowering initiation, and duration. Speed breeding eases multiple trait improvement in a shorter span by integration of high-throughput phenotyping techniques with genotype platforms. The crop breeding cycle is also shortened by the implementation of selection methods such as single-seed descent, single plant selection, and marker-assisted selection.

**Keywords:** accelerated breeding, controlled environment, crop Improvement, rapid generation advancement, speed breeding

### **1. Introduction**

The increase in world population coupled with climatic fluctuations such as drought, flood, and high temperature poses a serious threat to food security [1]. Many researchers quoted the importance of enhancing the genetic gain of primary crops at a faster rate to meet the global food demands [2]. It remains a challenging task for plant breeders to evolve resilient varieties in a shorter period by employing conventional approaches. The slow progress in crop improvement is mainly attributed to long breeding cycles/generation [3]. To overcome the drawbacks involved in traditional methods and to safeguard food security, speed breeding concepts are now being adopted at large/small units for realizing a rapid genetic gain in many crop species.

The speed breeding techniques include the use of controlled environments with manipulation provisions for the light duration, intensity, and temperature. This serves as more advantageous for the plant breeder to hasten the crop development

#### **Figure 1.**

*Rapid generation advancement through speed breeding. a. Experimental crop grown under controlled environments. b. Use of high-throughput genotyping platforms; advanced phenotyping tools and other modern breeding techniques in speed breeding protocol.*

in several major photosensitive crops [4]. The concept of stimulating an artificial environment for plant growth was first initiated by a team of botanists several years ago. Around 1980, similar protocols were again adopted by scientists of National Aeronautics and Space Administration (NASA) in collaboration with Utah State University to understand the accelerated crop growth cycle under constant light in the space station [5]. As an outcome, a new dwarf variety USU-Apogee was released by NASA in wheat [6]. In earlier crop improvement programs, the breeders employed few manipulations in conventional approaches such as the single-seed descent method [7], shuttle breeding [8], and haploid technique for rapid delivery of superior varieties. These were upgraded and combined with the use of other innovative technologies under the term speed breeding. Scientists achieved rapid generation advancement through the adoption of novel techniques such as marker-assisted selection, *in vitro* culture, high-throughput phenotyping, next-generation sequencing, genomic selection, and gene editing in the speed breeding protocols [9]. The speed breeding concept was first employed in *Triticum aestivum* (wheat) to investigate the seed dormancy trait under controlled conditions [10]. At present, speed breeding protocols are widely employed in several crops, including underutilized species [11]. Around six generations per year have been achieved in crops such as oat [12], barley [13], wheat [14], chickpea [15], faba bean, and lentil [16] through the implementation of speed breeding techniques. Speed breeding protocols allow for the integration of new techniques along with several manipulations in influencing factors (**Figure 1**), which have been briefly discussed in this chapter.
