Onion Male Sterility: Genetics, Genomics and Breeding

Onion, belonging to the Allium genus, is an essential and versatile vegetable crop that plays a pivotal role in culinary traditions worldwide. Renowned for its distinctive flavor and nutritional value, onion is an indispensable ingredient in countless dishes. As the global demand for onion continues to surge, securing a stable supply of high-quality, high-yielding onion varieties becomes ever more pressing. The onion umbel bears numerous tiny flowers that are protandrous in nature. Hybrid breeding is limited in onion due to high inbreeding depression, tedious emasculation and lack of elite inbreds. In this quest for crop improvement, the phenomenon of male sterility stands out as a key tool in modern onion breeding. Male sterility, which is recognized as the incapacity to produce viable pollen grains, inhibition of anther dehiscence and production of non-functional male gametes, has been harnessed as a mechanism to control cross-pollination and escalating hybrid development. The successful utilization of stable male sterile lines in onion holds the promise of producing uniform, high-yielding and disease-resistant hybrids. In recent decades, scientific advances have illuminated the molecular intricacies underlying male sterility systems in onion. Much progress has been made in elucidating the regulation of male sterility systems in the post-genomics era. This review highlights the current status of molecular markers linked with male sterility and provides genetic and molecular insights into its regulation. Additionally, it discusses the role of male sterility as a transformative tool in onion breeding in the genomics era.