Citation: Singh, H.; Sekhon, B.S.; Kumar, P.; Dhall, R.K.; Devi, R.; Dhillon, T.S.; Sharma, S.; Khar, A.; Yadav, R.K.; Tomar, B.S.; et al. Genetic Mechanisms for Hybrid Breeding in Vegetable Crops. Plants 2023, 12, 2294. https://doi.org/10.3390/ plants12122294 Academic Editor: Andreas W. Ebert Received: 19 April 2023 Revised: 25 May 2023 Accepted: 2 June 2023 Published: 12 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). plants Review Genetic Mechanisms for Hybrid Breeding in Vegetable Crops Hira Singh 1 , Bhallan Singh Sekhon 1 , Pradeep Kumar 2 , Rajinder Kumar Dhall 1 , Ruma Devi 1 , Tarsem Singh Dhillon 1 , Suman Sharma 3 , Anil Khar 4 , Ramesh Kumar Yadav 4 , Bhoopal Singh Tomar 4 , Theodora Ntanasi 5 , Leo Sabatino 6 and Georgia Ntatsi 5, * 1 Department of Vegetable Science, Punjab Agriculture University, Ludhiana 141004, India; hira@pau.edu (H.S.); bhallansekhon3249@gmail.com (B.S.S.); rajinderkumar@pau.edu (R.K.D.); rumadevi@pau.edu (R.D.); tarsemdhillon@pau.edu (T.S.D.) 2 ICAR—Central Arid Zone Research Institute, Jodhpur 342003, India; pradeep.kumar4@icar.gov.in 3 Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, NM 88003, USA; suman30@nmsu.edu 4 ICAR—Indian Agricultural Research Institute, New Delhi 110012, India; anil.khar@gmail.com (A.K.); rkyadavneh@gmail.com (R.K.Y.); bst_spu_iari@rediffmail.com (B.S.T.) 5 Laboratory of Vegetable Production, Department of Crop Science, Agricultural University of Athens, IeraOdos 75, 11855 Athens, Greece; ntanasi@aua.gr 6 Department of Agricultural, Food and Forest Sciences, University of Palermo, 90128 Palermo, Italy; leo.sabatino@unipa.it * Correspondence: ntatsi@aua.gr Abstract: To address the complex challenges faced by our planet such as rapidly changing climate patterns, food and nutritional insecurities, and the escalating world population, the development of hybrid vegetable crops is imperative. Vegetable hybrids could effectively mitigate the above- mentioned fundamental challenges in numerous countries. Utilizing genetic mechanisms to create hybrids not only reduces costs but also holds significant practical implications, particularly in streamlining hybrid seed production. These mechanisms encompass self-incompatibility (SI), male sterility, and gynoecism. The present comprehensive review is primarily focused on the elucidation of fundamental processes associated with floral characteristics, the genetic regulation of floral traits, pollen biology, and development. Specific attention is given to the mechanisms for masculinizing and feminizing cucurbits to facilitate hybrid seed production as well as the hybridization approaches used in the biofortification of vegetable crops. Furthermore, this review provides valuable insights into recent biotechnological advancements and their future utilization for developing the genetic systems of major vegetable crops. Keywords: hybrids; self-incompatibility; gynoecism; male sterility; pollen biology; biofortification; vegetables 1. Introduction Hybrids offer significant advantages for enhancing the economic and technological as- pects of vegetable cultivation, primarily due to the phenomenon of heterosis, which confers superiority over diverse parent varieties. Hybrids’ exploitation is of the utmost importance in addressing the emerging challenges induced by climate change, including the mitigation of food and nutritional insecurities. Moreover, hybrids provide a powerful tool for breeders to maximize the yield potential of vegetable crops. Heterosis exerts a profound impact on both productivity and quality across a range of vegetable crops, enabling improvements in livelihoods by enhancing productivity and delivering high-quality products and nutrition- ally superior food options. Leveraging genetic mechanisms to exploit heterosis facilitates enhancing productivity, improving quality (depending on the objective), and reducing seed production costs. The growing interest in heterosis exploitation and the utilization of genetic mechanisms is evident in the intensified investigation of self-incompatibility (SI), male sterility, and gynoecism and their applications in hybrid seed production for several Plants 2023, 12, 2294. https://doi.org/10.3390/plants12122294 https://www.mdpi.com/journal/plants