Molecular Techniques for Testing Genetic Purity and Seed Health

Abstract

With the globalization of seed trade and transgenic variety development, the application of molecular technologies for seed quality gained more significance in both the internal and international markets. Besides germination, genetic purity and seed health are the two most important seed quality parameters that determine the planting value of a seed lot. Compared to the conventional methods of testing, molecular marker technologies are more efficient for quality analysis as these are more accurate, robust, abundant, and faster. Among the various markers, simple sequence repeats (SSRs), due to their genome-wide presence, reproducibility, multi-allelic nature, and co-dominant inheritance, have emerged as the best markers, for establishing varietal distinctness, identity, and variety/hybrid seed purity testing. With the advent of the next-generation sequencing (NGS) technology, single nucleotide polymorphic (SNP) markers also became widely popular, and the closest to being an ideal marker besides SSRs, in seed genetic purity testing. With large-scale GM crop cultivation, testing for the adventitious presence and trait purity are two added components of seed quality testing. The methods of GM seed quality testing include DNA-based (conventional and real-time PCR), protein-based (lateral flow test and ELISA), and bioassay-based technologies. DNA-based methods including PCR/real-time PCR assays have been successfully employed to detect the adventitious presence of transgenic seeds in seed trade especially at international level, as well as in the national gene banks for germplasm conservation. ISTA plays a prominent role in international harmonization and providing universal guidelines on use of different methods to detect GM seeds. The BMT group of UPOV and the Working Group on DNA Methods of the Variety Committee of ISTA, work in tandem to standardize suitable molecular techniques for establishing variety identity and purity testing, respectively. In the area of seed health testing also, molecular detection assays such as, PCR (nested PCR, multiplex PCR, real-time PCR), loop-mediated isothermal amplification (LAMP), and DNA microarray with many advantages over the conventional assays have been proven highly useful. However, there is a need to validate the usefulness of molecular markers through stringent multi-laboratory tests for their reproducibility before recommending them in routine seed purity and health testing.