Breeding rice varieties with improved grain and nutritional quality

Abstract

Worldwide, 3 billion people depend on rice for more than 20% of their daily calorie intake. Like yield, rice grain quality has now become a primary consideration for producers and consumers. However, preference for grain quality is highly variable in different regions, countries and among different consumers. The grain consists of ª80% starch and its quality is dependent on a combination of several traits, some of which are influenced by environmental factors. The major physical traits include grain shape, size, chalkiness, degree of milling, and head rice recovery, and chemical characteristics-amylose content, gelatinization temperature and gel consistency. A number of Quantitative Trait Loci (QTLs) have been identified and molecular markers for some of the traits are available. Starch biosynthesis, however, is a complex system involving as many as 18 genes including starch synthases, branching and debranching enzymes, which act in concert to affect starch structure and function at least at six organizational levels. Aroma carries a special place in rice and is controlled by 1 or 2 major genes, and molecular markers for three alleles are available.