Abstract
The genus Allium includes approximately 750-800 species of geophytes with bulbs or rhizomes. Many Allium species were domesticated millennia ago as important foods, and today >20 species, characterized by onion-garlic-like flavor due to cysteine sulfoxides, are consumed worldwide as condiments, green vegetables, and nutraceutical foods. This chapter describes the (i) centers of origin and evolution; (ii) seedling development; (iii) bulbing physiology, including environmental and growth regulators controlling bulbing; plant factors influencing bulb yields; bulb maturation, dormancy, rest, and sprouting; effect of plant growth regulators on storage; genetic control and molecular biology; male sterility; fertilization and seed development; and (iv) physiological disorders of Allium. All studied Allium species exhibit strong interactions between genotypes and environment, which considerably affect growth, foliage development, yield and quality of storage organs, flowering, seed production, and seed quality. Very little is known about the roots and the endogenous mechanism that controls the formation of storage organs. The complex physiology (especially with regard to competition over resources between generative and storage organs) is far from being understood and molecular knowledge is rather poor. Utilization of both classical and novel tools for genetic and physiological studies, and improved knowledge of inherent control mechanisms of the initiation and development of vital processes, will facilitate improvements in terms of distribution, yield, and quality of these important crops, and provide the tools required for cultivation of these cold-requiring plants under the present and future global warming.