ABSTRACT
Rice is the staple food for more than half of the world’s population, which provides 27% of caloric need and 20% of the dietary protein intake (Fresco, 2005; Verma and Srivastav, 2017). About 90% of rice production and consumption were reported in Asian countries (Dutta et al., 2012). Giri and Vijayalakshmi (2000) reported that by the year 2050 the world population is estimated to be approximately 11 billion people out of which 90% of the people reside in the developing countries of the South. As rice is considered as the staple food for the tropical and subtropical region people, the increase in rice yield is a must especially in Asia (Cha-um et al., 2009). In India, there are lots of indigenous traditional rice varieties which are economically valuable due to properties like aroma, medicinal properties, grain yield, short duration, and so forth. The fragrant or aromatic rice are the special varieties that emit delicious fragrance when cooked (Itani et al., 2004). Due to its pleasant aroma, it is preferred over non-aromatic rice varieties (Joshi and Behera, 2006; Nadaf et al., 2006). Aroma content of the rice is the primary selection criteria employed for its assessment of quality (Reinke et al., 1991; Verma and Srivastav, 2016). Most of the aromatic rice varieties are cultivated in the regions of India, Thailand, and Pakistan. Basmati rice in India is considered to be one of the most widely used aromatic rice across the world due to its exquisite aroma. In India, there are many indigenous aromatic rice varieties apart from Basmati, which are small, medium grained and good in fragrance (Nadaf et al., 2006). Gandhakasala and Jeerakasala are fine white rice varieties grown in South India which are believed to contain fragrance and also having the high grain yield of 2743 and 2179 kg/ ha respectively. Gandhakasala and Jeerakasala are traditionally believed to be aromatic rice varieties (George et al., 2005). Due to difficulty in cultivation and lack of scientific data, these valuable rice genotypes are in the verge of extinction though it has many special traits, especially aroma, medicinal properties, and so forth. Buttery et al. (1983a) reported that there are more than 114 volatile compounds responsible for aroma in the aromatic rice varieties. Among these volatile compounds, 2-acetyl-1-pyrroline (2AP) is the principal compound which imparts delicious popcorn-like flavor to the rice varieties which is mostly controlled by the loss function of betaine aldehyde dehydrogenase gene (badh2 of fgr) on rice chromosome 8. The non-aromatic rice also contains 2AP, but 10-100 times lower than that of the aromatic variety (Buttery et al., 1983a; Laksanalamai and Ilangantileke, 1993). A recessive gene (fgr gene) located on exon 7 of the Chromosome
8 is proved to be responsible for the rice fragrance. Therefore, the 2AP analysis, by both quantitative and qualitative analysis, is essential to identify the rice variety as aromatic or non-aromatic in order to reveal its economic importance. In vitro callus induction and plant regeneration are the essential prerequisite for crop improvement, conservation and genetic transformation studies (Bhaskaran and Smith, 1988). The effective callus formation and regeneration is considered as variety specific (Saharan et al., 2004) and the efficient regeneration in indica rice varieties is still a major problem as rice is considered as recalcitrant (Sathishkumar and Manoharan, 1996) which limits the genetic transformation studies towards those rice varieties. Although a copious literature reporting the in vitro regeneration from different explants exists (Karthikeyan et al., 2009), very little is reported about the efficient and high-frequency regeneration particularly for these rare Indian rice varieties. Establishment of the in vitro system is necessary for both crop improvement and to conserve these valuable natural resources from extinction. In this report, the 2AP content was analyzed by sensory analysis, histochemical staining, quantified by gas chromatography (GC) method and an efficient methodology for the in vitro regeneration is optimized which can be applied for the improvement of these rare cultivars with medicinal applications and also ensures the protection of these valuable rice varieties from the verge of extinction.
