Inheritance of Aroma in Six Rice Cultivars

'Jasmine 85', a soft-cooking aromatic rice (Oryza sativa L.) cultivar, was released in the USA with the objective of displacing imported Thai Jasmine rice in local markets. However, the reduced aroma and off-white color of its milled rice limit its marketability. The present objective was to determine the number of genes controlling aroma in four rice lines (Jasmine 85, 'Amber', a dwarf mutant from 'Basmati 370' (P1 457917), and 'Dragon Eyeball 100'), and to evaluate the allelism of aroma in these four lines and with the single recessive gene known to be in both 'A-301' and Della-X2. Lack of leaf aroma in aromatic/non-aromatic Ft hybrids indicated the recessive nature of the aroma in all studied rices. F2 segregation ratios revealed that Jasmine 85 and P1 457917 each contain a single gene for aroma, and the aromatic nature of the Ft leaves from crosses with each other and with A-301 and Della-X2 revealed that the aroma genes in all four cultivars are allelic. Amber and Dragon Eyeball 100 each contain two aroma genes, a novel gene plus one allelic to the gene in A-301, Della-X2, Jasmine 85, and P1457917. Incorporation of a novel aroma gene into Jasmine 85 could potentially increase its marketability. No linkage was detected between the two aroma genes in Dragon Eyeball 100 and five morphological characters. High levels of sterility observed in Amber F2 populations may hinder the use of its novel aroma gene. I SPITE OF A SURPLUS of domestically grown rice, the volume of imported rice is increasing in the USA (Wailes and Livezey, 1991). Ninety percent of these imports are milled rice from Thailand. Most are of the Jasmine type, an aromatic, soft-cooking type of rice sold primarily in U. S. Asian markets (Wailes and Livezey, 1991). Jasmine 85 was released in the USA to compete with imported Jasmine rice (Bollich, 1989). However, when U. S. grown Jasmine 85 was evaluated by Thai Jasmine consumers and professional taste panels, it was consistently criticized for its dull off-white color and less pronounced aroma (Rister et al., 1992). The aromatic character of Basmati rice and Thai Jasmine has been attributed to 2-acetyl-l-pyrroline, which is present in all rice, but is present in significantly higher concentrations in these aromatic cultivars (Buttery et al., 1983, 1986). Lin et al. (1990) determined that the level of this aromatic USDA-ARS, Texas AM Sood and Siddiq, 1978; Reddy and Reddy, 1987), 3:1 ratios indicating a single dominant aroma gene (Kadam and Patankar, 1938), 15:1 or 9:7 ratios indicating two dominant aroma genes interacting in a duplicate or complimentary manner (Dhulappanavar and Mensinkai, 1969; Tripathi and Rao, 1979), 37:27 ratios indicating three complementary recessive aroma genes (Reddy and Sathyanarayanaiah, 1980; Nagaraju et al., 1975), 175:81 ratios indicating four complementary recessive aroma genes (Dhulappanavar, 1976), and 3:13 ratios indicating a single recessive aroma gene interacting with an inhibitor gene (Ghose and Butany, 1952; Tsuzuki and Shimokawa, 1990). The differing observations may have been due to the cultivars used in the various studies and to the use of different techniques and materials for detecting aroma. Berner and Hoff (1986) stressed the importance of using blind controls as well as selecting plant materials and sample sizes that are appropriate for an endosperm character, like aroma, where heterozygous plants are expected to produce both aromatic and non-aromatic seed. The objective of the present study was to determine the number of aroma genes and their allelic relationships in six aromatic lines. It was hoped that additional aroma genes could be found that could be introduced into Jasmine 85 to increase its aromatic character, thus increasing its marketability. MATERIALS AND METHODS