Screening of aromatic rice lines by phenotypic and molecular markers

To improve the yield potential of local aromatic variety Kalizira, a segregating population was developed from a cross between Y-1281 (high yielding mutant variety) and Kalizira. Thirty two F7 rice lines were used to evaluate agronomic characteristics, aroma detection through sensory test and genotypic analysis using microsatellite markers. Highly significant negative association was found between aroma and grain yield. Nine, 12 and 17 pedigree lines (PLs) having fragrance gene ( fgr) locus were found using three SSR markers RM223, RM342A and RM515, respectively as homozygous condition in 32 rice lines. The marker RM515 detected highest number of fgr locus in PLs. Fourteen promising lines were identified with aroma genes having higher yield with good agronomic performance and other grain quality traits. These SSR markers could be utilized in marker -assisted selection (MAS) and would have a great impact on identifying fgr locus in rice genotypes. Rice (Oryza sativa L.) is the staple food of more than half of the world's population. Most of the world's rice is produced and consumed in Asia which constitutes more than half of the global population (Chakravarthi and Naravaneni 2006). In Bangladesh rice occupies about 70% of t he total cropped area of about 13.9 million hectares. Out of this 70%, fine rice is cultivated in roughly 10% land. Grain quality in rice plays an important role in consumer acceptability. Juliano and Duff (1991) concluded that grain quality is second afte r yield as the major breeding objective for crop improvement. The quality in rice is considered based on milling quality, grain size, shape, appearance, aroma and other cooking chara cteristics (Dela Cruz and Khush 2000). Most of the scented rice varieties in Bangladesh are of traditional type, photoperiod sensitive, and cultivated during the Aman season. Majority of these indigenous aromatic rice cultivars are low yielding but its higher price and low cost of cultivation generate higher profit margins compa red to other varieties. Aroma development in rice grain is influenced by both genetic and environmental factors. The biochemical basis of aroma was identified as 2 -acetyl-1-pyrroline (Tanchotikul and Hsieh 1991). Most of the rice varieties have been develo ped traditionally by selection, hybridization and back crossing with locally adapted high -yielding lines. The conventional methods of plant selection for aroma are not easy because of the large effects of the environment and the low narrow sense heritabili ty of aroma. More recently molecular markers, such as SNPs and simple sequence repeats (SSRs), which are genetically linked to fragrance and have the advantage of being inexpensive, simple, rapid and only requiring small amounts of tissue, have been developed for the selection of fragrant rice (Cordeiro et al. 2002). Moreover, an allele specific amplification (ASA) assay allows discrimination between fragrant and non -fragrant rice varieties and identifies homozygous fragrant, homozygous non -fragrant and heterozygous non- fragrant individuals in a population segregating for fragrance (Louis et al. 2005). SSR or microsatellite markers behave as a co -dominant marker which was used for this study to select rice lines having aroma with fine grain and good seed yi eld.