Aromatic Rice and Factors Affecting Aroma in Rice

Aromatic rice is considered as an important value-added commodity with small variations in the aroma determining preference and unacceptability by the consumers. Aroma is the most desired trait followed by taste and elongation. Indian sub-continent is home to aromatic rice diversity with northeast being the richest reservoir of the genetic variability of aromatic rice. Aromatic rice has two groups, the long-grained Basmati type and the small and medium-grained indigenous aromatic varieties. 2-acetyl-1-pyrroline (2AP) is the principal component responsible for aroma, produced through a single recessive allele (fgr) at a locus on chromosome 8 which corresponds to the gene that encodes betaine aldehyde dehydrogenase (BADH2). A premature stop codon upstream of key coding regions is introduced by an 8-bp deletion in exon 7 which makes BADH2 non-functional. The mutant BADH2 transcript leads to 2AP accumulation in aromatic rice. The flow of γ-aminobutyraldehyde (GAB-ald) to γ-aminobutyric acid (GABA) is inhibited and consequently, the accumulated GAB-ald is diverted to a flavour component, 2-acetyl-1-pyrroline (2AP) by a non-enzymatic reaction with methylglyoxal. Accumulation of 2-acetyl-1-pyrroline in aromatic rice depends on the interaction of various genetic and environmental factors. Aromatic rice is prone to biotic and abiotic stress. Grain quality of aromatic rice can be improved using existing aromatic genotypes by backcrossing, mutation breeding or conventional cross-breeding. There is an urgent need to document, evaluate and conserve underutilized germplasm for the improvement of aromatic rice in the future.