A universal method for rapid identification of alfalfa and burr medic seeds with an emphasis on discriminating different forage species

Unlike many crop seeds which are large in size, forage seeds are relatively small. Moreover, some forage seeds from the same genus, or even different genera, share similar morphologies in terms of colour, size, weight and so on. Alfalfa (Medicago sativa L.) and burr medic (Medicago polymorpha L.) also share similar morphology. However, alfalfa is a perennial, cross-pollinated herbaceous species, whereas burr medic is considered an annual, self-pollinating plant. Therefore, a universal and rapid method of discriminating burr medic seeds from alfalfa seeds or other similar forage seeds from different plant species is needed. Previous methods of discriminating similar-looking forage seeds have been shown to be unreliable or time consuming. Here, a universal method that combines polymerase chain reaction (PCR) and polyacrylamide gel electrophoresis techniques was developed to discriminate alfalfa and burr medic. Based on the differences in the lengths of homologous genes caused by insertions and deletions between two species, a pair of primers was designed to discriminate the accessions of 15 alfalfa and 9 burr medic via visualizing the clearly different PCR amplicon sizes. In addition, the melting curve analysis was performed to investigate the specificity and reliability of the primer pair. The results showed two different melting peaks between the two species, further demonstrating this method can accurately and sensitively identify the two species. Thus, we believe that this method has the great potential to be extensively applied for the identification of contaminated seeds and breeding of forages.