Professor Dr. Apichart Vanavichit, Rice Science Center, Kasetsart University, explains how DNA technology can be used as a tool to control the quality of premium Thai Hom Mali rice.
A grassroots product
Hom Mali rice is widely grown on large paddy fields in poor, low-rainfall areas of northeastern Thailand. With infertile soil and inefficient irrigation in the Northeast, Hom Mali rice yields are low, so the product is scarce and expensive. Because of the high price of Thai Hom Mali rice, other rice varieties are often mixed in for export.
Export performance
Hom Mali rice is regarded as the world's number one aromatic rice and is an important export variety for Thailand. Since the variety was discovered in rural paddy fields and named Hom Mali 56 years ago, Thailand exported 1.4 million tonnes of Hom Mali rice between 2010 and 2019, 18% of all rice exports. Thai Hom Mali rice and Basmati (an Indian variety) are the most expensive rice varieties in the world. Cooked Thai Hom Mali rice has a natural fragrance, a soft and delicate texture, and excellent taste, so there is no doubt about its quality. Since 2009, Thai Hom Mali rice has won the World's Best Rice award five times. This is the main reason Thailand should have effective quality control measures, from seed management through to the quality of rice served at the table.
National Hom Mali rice standard
Thai Hom Mali rice is adulterated with low-quality white rice varieties that look physically similar, both in Thailand and abroad. Adulteration may be intentional or unintentional; the main cause is farmers' seed storage, and the second is farmers sharing combine harvesters, which causes unintentional mixing. Post-harvest adulteration is more complex because of the many stakeholders involved, such as local mills, exporters and importers. To reduce fraud through varietal adulteration, the Ministry of Commerce (MOC) set a national standard for Thai Hom Mali rice under the brand name "Thai Hom Mali Rice" for export, requiring genetic purity of not less than 92% for acceptance as high-quality Thai Hom Mali rice, recognizing that other varieties may be unintentionally mixed in during planting and harvesting.
Why genetic purity testing is the standard for rice quality control
Thai Hom Mali rice, officially named Khao Dawk Mali 105 (KDML105), has had its genetic purity confirmed and has been called Hom Mali rice since 1959. The RD15 variety was later developed from KDML105 by mutation breeding using gamma irradiation. Both varieties are regarded as Thai Hom Mali rice because their grain quality cannot be told apart.
DNA technology
Applying DNA technology to verify the authenticity of Thai Hom Mali rice varieties is widely accepted as key to supporting export standards. For high accuracy, specific molecular markers are used to test purity through the genetic composition of Thai Hom Mali rice. The DNA Technology Laboratory (DNA TEC) developed an in-house, state-of-the-art, low-cost single-grain molecular test for varietal adulteration. Exporters can submit samples to receive an official certificate of Thai Hom Mali rice variety authenticity, and only DNA TEC can provide this accurate information on varietal adulteration. Since 2012, DNA TEC has tested more than 54,472 Hom Mali rice samples, using up to 1.5 million polymerase chain reactions, and its newly established laboratory can now test up to 50,000 samples a year, enough to support 2 million tonnes of premium Thai Hom Mali rice for export (Figure 1).
Post-auditing system for Thai Hom Mali rice
To apply DNA technology to improve the export competitiveness of Thai Hom Mali rice, the Department of Foreign Trade, Ministry of Commerce (DFT, MOC) upgraded its post-auditing system, involving local mills and exporters, using fully accurate DNA technology. Farmers can sell paddy to certified local mills for processing; certification is carried out through provincial government offices, and certified mills receive the "Thai Hom Mali Rice" trademark from the DFT for export rights (Figure 2). Exporters can in turn use the same testing to buy Hom Mali rice directly from farmers for processing and export under the national brand. DNA TEC plays an important role for local mills and exporters in testing the purity of rice varieties harvested by farmers before processing. The DFT often randomly samples export-ready rice from warehouses, or even during exporters' transport, and tests it within 24 hours for rapid varietal purity results by the laboratory. Even in customers' warehouses in export markets, Thai Hom Mali rice is checked by Thailand's international consulate offices for genetic purity to prevent varietal adulteration before it leaves Thailand.
Economic impact
Strict regulation to assure the export quality of Thai Hom Mali rice has improved its genetic purity. In 2012, samples with purity of 92% or above made up 56% of all samples submitted; eight years later this rose to 66% (source: DNA TEC). DNA-based varietal purity testing helps increase economic opportunity. Studies show it affects price and export volume: over the eight years from 1992 to 2000, export volume increased by 279,000 tonnes a year, with total export revenue over the eight years of 86,117 million baht, more than before DNA-based testing. This raised farmers' income by 1,280 million baht a year, or 11,521 million baht over the eight years.
Vision for the future
DNA-based varietal purity testing is being developed to test other premium Thai export varieties, such as Riceberry, soft aromatic rice and soft rice, to meet new needs. DNA TEC has adopted new molecular-level testing technology for greater accuracy, and continues to look for cheaper and faster technology for rice purity testing that can be used outdoors and in the field, to lower costs for rice exporters and strengthen the competitiveness of premium Thai rice in the world market.
References
Vanavichit A, Kamolsukyeunyong W, Siangliw M, Siangliw JL, Traprab S, Ruengphayak S, Chaichoompu E, Saensuk C, Phuvanartnarubal E, Toojinda T, and Tragoonrung S. 2018. Thai Hom Mali Rice: Origin and Breeding for Subsistence Rainfed Lowland Rice System. Rice (2018) 11:20
Tragoonrung, S. 2018. The 10 Years DNA Technology Laboratory. http://dnatec.kps.ku.ac.th
DNA Technology Laboratory providing genetic purity testing of all biological substances and foodstuffs http://dnatec.kps.ku.ac.th