1 allele was detected in both the Japonica and Indica groups, the Cornell-IRRI team set out to determine in which group it had originated.

To do this they examined 242 different rice types from 38 countries across Asia and used what is called 'a haplotype approach', Susan McCouch, Cornell University researcher and one of the authors, said in an e-mail interview.

She said the haplotype analysis allowed the team to demonstrate that the badh2.1 allele -- responsible for fragrance -- arose within the Japonica group in a 'Basmati-like ancestor' and was transferred to fragrant Indica varieties, including the Jasmine varieties from Thailand.

The authors said the transfer of the fragrance gene would have occurred 'between the rice subpopulations through the process of introgressive hybridisation, facilitated by population expansion and human migration throughout Asia'.

Over 100 volatile compounds have been detected in fragrant rice varieties, but the major compound responsible for the characteristic aroma is 2-acetyl-1-pyrroline (2AP). Basmati grains contain 0.09 parts per million of 2AP which is about 12 times more concentration than un-scented rice varieties.

E.A. Siddiq, a renowned rice scientist and former deputy chief of the Indian Council of Agricultural Research, says the reported finding is purely of academic interest and has no commercial value.

'It makes no difference where Basmati derived its aroma from,' Siddiq told IANS. 'The most important trait of Basmati is elongation -- on cooking the grain length increases by as much as two-and-half times.'