Onion (Allium cepa L. ) 2n=16.

It is a highly cross-pollinated, biennial for seed production and annual for bulb production, belonging to family Alliaceae. Onion is one of the most important vegetables and grown worldwide under outdoor condition.

It has become an important commercial crop because of its area, production and consumption. During the past few decades tremendous developments have contributed to the knowledge and understanding of various aspects of crop production and various literatures has been generated.

To improve the bulb yield and quality through selection of better varieties, the information on the nature and magnitude of variability for yield and other characters present in the population owing to its genetic and non-genetic causes play an important role and as such it is a pre-requisite for any systematic breeding programme. The crop yield being complex in nature depends largely on its contributing characters and their interactions.

Knowledge on association of these traits with yield will be more useful to plan the selection strategies for improving the yield. With going this book many ideas and problems are discussed to help out the students, research workers.

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