Chapter 7 **The CRISPR/Cas9 System for Crop Improvement: Progress and Prospects 129**

Kah-Yung Bernard Leong, Yee-Han Chan, Wan Muhamad Asrul Nizam Wan Abdullah, Swee-Hua Erin Lim and Kok-Song Lai

Preface

crops.

feed an ever-growing population.

ance from the public and policymakers.

Today, the major challenges of agricultural production include unpredictable and extreme weather conditions that cause abiotic stress together with the severity and distribution of many pathogens and pests. Furthermore, climate change and decrease in the availability of arable land per person also cause severe limitations. Thus, we need more crop production to

The potential solution to this problem could be the development and utilization of modern genomics and biotechnological tools, which can provide a second Green Revolution as a complementary strategy to conventional breeding. This was also pointed out by Nobel Peace Prize Laureate Dr. Norman E. Borlaug in 2000 (Plant Physiol. 124:487–490). In accord‐ ance, currently, several successful examples that apply molecular tools have effectively con‐ tributed to developing cultivars in rice, millet, maize, several legumes, and horticultural

In this sense, next-generation breeding techniques, including marker-assisted selection (MAS), next-generation sequencing (NGS), gene editing techniques, together with omic technologies, including genomics, transcriptomics, proteomics, and phenomics, have great potential not only to develop new crop cultivars but also to increase crop tolerance to abiotic and biotic stresses for sustainable agriculture. Among them, MAS could be regarded as a precise and efficient selection system that allows for recessive allele selection at early-stage selection and multiple genes pyramiding without traditional phenotypic evaluation for each trait. NGS and powerful computational pipelines have appeared as powerful tools both to identify many DNA sequence polymorphism-based genetic markers and to determine gene expression levels with RNA-sequencing (RNA-seq) methods within a short time and at low cost. However, there is still a necessity to increase the number of available high-quality whole-genome reference models and crop plant sequences to accelerate gene mapping and discovery to aid the application of MAS. Hence, information on genome sequences and gene functions is also a precondition for effective genome editing, which represents a new breed‐ ing technology that enables targeted or directional breeding with its low cost, precision, and rapidness in spite of the challenges (nontarget effects and regulations) that have to be re‐ solved. Last but not least, it is obvious that the abovementioned next-generation plantbreeding techniques will be a frontier area of plant science and business for the cultivation of crops for tomorrow. Thus, we need a broad interdisciplinary approach both to transmit the information and experience obtained with model plants to crops and to achieve accept‐
