DNA authentication of tulsi (Ocimum tenuiflorum) using the nuclear ribosomal internal transcribed spacer (ITS) and the chloroplast intergenic spacer trnH-psbA

DNA barcoding, a technique used to identify species based on short regions of DNA [1], can discriminate between different species, and identify contaminants and adulterants. Ocimum tenuiflorum L., commonly known as holy basil or tulsi, is native to Asia. Three types of tulsi are recognised in the Hindu culture (figure 1); Raam and Shyam (Krishna) are varieties of O. tenuiflorum, whilst Vana tulsi is O. gratissimum L. [2]. Following migration, tulsi plants are widely grown in South Asian (SA) households across the UK. The aim of this research is to use DNA barcoding techniques to identify tulsi plants collected from SA families, using ITS and trnH-psbA regions.

A variety of tulsi samples were collected for authentication: community samples from SA families in the UK, commercial samples, and vouchered specimens. DNA analyses discovered that samples described as Shyam tulsi collected from communities in the UK were O. tenuiflorum, but Raam tulsi samples were O. gratissimum. Commercial samples proved to be recalcitrant to DNA extraction; this could be because the DNA had been degraded during manufacturing processes. Vouchered specimen obtained were used to create reference DNA barcodes which were not available in the current DNA databases.

Both ITS and trnH-psbA regions were successfully used to distinguish between O. tenuiflorum and O. gratissimum samples. The plastid trnH-psbA primers were more efficient for amplification and sequence analysis than the ITS region. The results exemplify how with the transmission of traditions from one country to another, confusion of species is occurring. Both the ITS and trnH-psbA regions had their strengths and limitations which reinforces the importance of using multiple primers for species authentication.

Fig. 1: Tulsi plants in India

References:

[1] Kress WJ et al Use of DNA barcodes to identify flowering plants. PNAS, 2005; 102:, 8369 – 8374

[2] Joshi V et al. Pharmacognostic and scientific evaluation of the plant – tulsi (O. sanctum). IJGHC, 2012; 1: 75 – 90