Reproductive Biology, Sterility and Fertility Restoration, Breeding and Biotechnological Advances in Garlic: A Comprehensive Review

Abstract

Garlic reproduces asexually, as its flowers are generally partially or completely sterile. In some garlic populations, inflorescences often exhibit small aerial bulbs, called ‘bulbils’, which are believed to compete for photoassimilates with developing flowers, thereby influencing fertility. Recent physiological studies on a few fertile genotypes and successful restoration of fertility by removing bulbils from inflorescences and growing the plants under long day conditions have suggested the potential possibility of commercial true seed production in garlic. Additionally, advances in garlic research using cutting edge technologies, including genomic assisted breeding, QTL and simply-inherited trait mapping, genome wide association studies (GWAS), transcriptomics, metabolic engineering and somaclonal variation, have contributed to our understanding of underlying causes and mechanisms of garlic sterility, although, to date, this has not been completely elucidated. As a result, large-scale commercial seed production of garlic is not currently possible. Thus, current breeding strategies should focus on the selection of those—rather infrequent—clones with fertile flowers, and inflorescences with few and small bulbils, exhibiting high yields of large and viable seeds. This review summarizes and critically discusses results from over 30 years of research on garlic reproductive biology, its sterility and reported cases of fertility restoration, and the approaches used for true seed production in the species. Genetic, physiological and morphological factors affecting this trait are discussed. Unlocking garlic's sexual reproduction would have a tremendous positive impact in breeding, genetic research, and—ultimately—domestication of this flavourful vegetable.