Abstract:
Aromatic rice is highly cherished in many countries of the world and commands premium prices at all levels of the global rice trade. The presence of aroma in aromatic rice is controlled by betaine aldehyde dehydrogenase 2.1 (BADH2.1) gene allele which results from an eight base pair deletion and three single nucleotide polymorphisims (SNPs) in exon seven of betaine aldehyde dehydrogenase 2 (BADH2) gene. This mutation is responsible for the introduction of premature stop codon which produce a truncated protein, this results in loss of function of the enzyme betaine aldehyde dehdrogenase 2 (BADH2) leading to accumulation of substrate (main aroma compound) 2-acetyl 1-pyrroline (2AP) in aromatic rice varieties. In this study, the association between BADH2.1 aromatic allele and aroma in Tanzanian rice varieties was investigated. Leaf and grain aromatic tests for aroma evaluation and screening for BADH2.1 gene allele using allele specific amplification (ASA) marker were conducted in 160 popular traditional rice landraces from different geographical regions of Tanzania. Of the 160 landraces genotyped and phenotyped; 95 varieties were classified as aromatic by the presence of aroma in both leaf and grain aromatic tests, most of these (91.6 %) carried BADH2.1 gene allele. Evidence from sequencing of BADH2/BADH2.1 alleles confirmed the association of BADH2.1 gene allele with aroma in aromatic rice landraces as it was shown that all aromatic genotypes had eight base pair deletion and three SNPs in exon seven of BADH2 locus. This suggests that BADH2.1 gene allele is the main aroma allele in most of the Tanzanian aromatic rice varieties. Phylogenetic analysis of BADH2/BADH2.1 nucleotide sequences, showed a large amount of genetic variability (39.41-100 % nucleotide sequence identity) among the varieties studied. These findings will contribute siginificantly in planning for effective rice breeding strategies especially in selection of appropriate parental materials for developing high yielding aromatic rice varieties in the country.
