Studying bulb formation in Onion was very intersting to me, behind the environmental factors that effect bulb formation, Genetics factors still big mistry for this subject. However, I focused in both environmental and Genetics factors that effect bulb formation in Onion. As result, I found that Onion is very sensitive plant to the environment and how is this sensitivity important to the Onion breeder around the world. In addition, genetics effect bulb formation in Onion still not understanding very well, but I mention the important genes that may effect the bulb formation in Onion.