**1. Introduction**

Fruit and vegetable crops are rich in cellulose, vitamins, trace elements, minerals, and other important nutrients, which are essential in the human diet [1]. However, climate and environmental changes potentially threaten the production and supply of fruits and vegetables [2]. Humans have long domesticated and cultivated wild species. Crossbreeding technology enables breeders to improve varieties by crossing selected dominant varieties [3]. However, with long-term artificial selection, the shortcomings of conventional breeding become increasingly prominent, mainly in the excessive dependence on naturally occurring allelic variation. There are limited genetic germplasm resources for improving target traits, and conventional breeding can expose many adverse traits, thereby reducing breeding efficiency [4]. Although traditional breeding can produce new vegetable cultivars with high yield, good quality and disease resistance, with the increasing global population and continuous food-supply demands, it is important to rapidly select new varieties to meet market demands [5]. The development and application of emerging methods in crop biotechnology can promote high-efficiency and precise varietal breeding [6].

Genetic engineering has been used to improve the responses to biotic and abiotic stress, and to improve the quality of fruits and vegetables. In 1994, a storage resistant transgenic tomato was approved by the Food and Drug Administration (FDA) [7]. For papaya, 80%

**Citation:** Wan, L.; Wang, Z.; Tang, M.; Hong, D.; Sun, Y.; Ren, J.; Zhang, N.; Zeng, H. CRISPR-Cas9 Gene Editing for Fruit and Vegetable Crops: Strategies and Prospects. *Horticulturae* **2021**, *7*, 193. https:// doi.org/10.3390/horticulturae7070193

Academic Editor: Yuyang Zhang

Received: 1 June 2021 Accepted: 10 July 2021 Published: 14 July 2021

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of the market was supplied with high-yield transgenic papaya with high resistance to the cyclic spot virus [8]. However, in order to ensure safety in planting processes and product consumption, genetically modified (GM) plant development and application are strictly legislated and regulated, greatly delaying the development to market of transgenic cultivars [9]. In 2013, CRISPR-Cas-mediated gene editing was developed as a tool to study plant gene function. Over the next two years, many new gene-edited crop germplasm resources emerged. In 2016, the US FDA approved the CRISPR gene editing of a waxy corn null segregant line and an anti-browning mushroom (*Agaricus bisporus*) for the market, without applying the strict regulatory process required for GM crops [10,11]. This indicates that CRISPR gene editing has already succeeded in promoting the development of crop cultivars.

In this review, we summarise the mechanisms underlying CRISPR technology, recent applications in fruit and vegetable crops, and improvements in CRISPR-Cas systems. We further outline CRISPR-associated regulatory frameworks that enable commercialisation of gene edited crops in different countries. Finally, we discuss the future challenges and opportunities for introducing desirable alleles and improving many traits.
