INTRODUCTION

Rice is principally a crop of tropical and semi-tropical regions, but is also grown in many cold regions of the world in late spring to summer. It is most susceptible to chilling temperatures amongst abiotic factors and experiences a greater yield loss.

Rice is a staple food for two third of the population of the world and is basic part of diet. As a cereal grain, it is the most widely consumed staple food for a large part of the world's human population, especially in Asia and the West Indies. It is the grain with 2nd highest worldwide production after maize (corn), according to the data of 2010. Since a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and calory intake, providing more than one fi fth of the calories consumed worldwide by the human species.