Abstract
Rice (Oryza sativa L.) is one of the most cultivated and consumed crops worldwide. It is mainly produced in Asia but, due to its large genetic pool, it has expanded to several ecosystems, latitudes and climatic conditions. Europe is a rice producing region, especially in the Mediterranean countries, that grow mostly typical japonica varieties. The European consumer interest in rice has increased over the last decades towards more exotic types, often more expensive (e.g., aromatic rice) and Europe is a net importer of this commodity. This has increased food fraud opportunities in the rice supply chain, which may deliver mixtures with lower quality rice, a problem that is now global. The development of tools to clearly identify undesirable mixtures thus became urgent. Among the various tools available, DNA-based markers are considered particularly reliable and stable for discrimination of rice varieties. This review covers aspects ranging from rice diversity and fraud issues to the DNA-based methods used to distinguish varieties and detect unwanted mixtures. Although not exhaustive, the review covers the diversity of strategies and ongoing improvements already tested, highlighting important advantages and disadvantages in terms of costs, reliability, labor-effort and potential scalability for routine fraud detection.
Highlights
DNA barcoding explores a unique pattern of variation in a DNA section or gene that allows the specific identification of a species or variety, and it was already proposed as a standardized method [102]
A method combining High Resolution melting (HRM) with DNA barcoding, known as Bar-HRM [119], has shown to be successful for quantitative determination of adulterants in agri-food products [119,120,121] it was still not explored in rice. This methodology uses sequences derived from barcoding markers, to design specific primers that allow the amplified region to be used in post-Polymerase Chain Reaction (PCR) HRM [119]
The increase of whole-genome rice data, boosted by the 3K project and led by the advances in sequencing technologies and bioinformatic tools, opened the door for the identification of an exponential number of new DNA-based markers. This will definitely contribute to the development of new methodologies for rice authenticity analysis
Summary
Rice is a major crop that directly feeds about half of the global population, most of it in developing countries [1]. Following a tendency for human population growth (12% from 2010 to 2020), global rice production has risen in the same period, reaching 500 million tons (13% increase) [2] This was possible due to improved agronomic practices and improved varieties. To better explore the molecular diversity of this germplasm, a large sequencing initiative, the 3K Rice Genome Project [4], was launched by the Chinese Academy of Agricultural Sciences, Foods 2022, 11, 258. To better explore the molecular diversity of this germplasm, a large sequencing initiative, the 23oKf 21 Rice Genome Project [4], was launched by the Chinese Academy of Agricultural Sciences, BGI-Schenzhen and the International Rice Research Institute (IRRI). This increase in EU importations of japonica rice, has led to some of the biggest consumer countries to come together to promote EU japonica rice production and sales in the European market [20]
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