Characterization and evaluation of tulsi (Ocimum tenuiflorum L.)

Abstract

Medicinal and aromatic plants (MAPs) have been ingredients of traditional medicine since time immemorial. Ocimum tenuiflorum L. (synonym Ocimum sanctum), commonly known as holy basil or tulsi, is an aromatic and medicinal plant native to Indian subcontinent. This plant is known to produce essential oils comprising of a number of aromatic compounds and has immense use in traditional system of medicine, perfumery, and pharmaceutical industry and hence known as the “queen of herbs”. Tulsi is a valuable herb with diverse potential. Almost all parts such as leaves, stem, flower, roots and seeds of tulsi have been used in numerous formulations of Ayurvedha, Sidha, Unani and Homeopathy. However, as a commercial crop it is less exploited in Kerala. Hence the present study entitled “Characterization and evaluation of tulsi (Ocimum tenuiflorum L.)” was taken up in the Department of Agronomy, College of Agriculture, Vellanikkara. The objectives of the study included evaluation of Ocimum tenuiflorum L. accessions for yield and quality, standardization of shade requirement and method of harvesting, investigation of allelopathic effect on upland weeds and crops, and also assessment of the effect of tulsi on root-knot nematode (Meloidogyne incognita). Thirty five accessions of tulsi (10 NBPGR accessions + 25 local collections) from different locations were evaluated for morpho-physiological, biochemical and yield characters. High degree of variation was observed among accessions for all the parameters studied. The collected accessions were grouped into three morphotypes based on the colour of stem, upper leaf surface and inflorescence. Out of the 35 accessions, 16 were identified as green types, 14 were purple types and 5 were intermediate. The collected accessions were grouped into six clusters using eight quantitative characters. Principal component analysis revealed that first three principal components (plant height, mumber of primary branches and secondary branches) ii contributed for 79.7 per cent of variability. Based on biochemical characters (chlorophyll, carotenoid and essential oil content), 35 tulsi accessions were placed into five clusters and the first principal component (chlorophyll content) accounted for 89.90 per cent of the total variation. The logistic binomial estimate revealed that colour had a positive relation with essential oil contentand the expected percentage of improvement f o r essential oil content over the base population was 80.41 per cent.Scoring and ranking based on total biomass yield, number of primary branches and leaf area index revealed accession IC 583288 to be the top rank holder, followed by IC 583318, IC 583296 and KAU OC 30. Based on essential oil content and carotenoid, the best performing accessions were KAU OC 25, KAU OC 34 and KAU OC 32. Accessions IC 583288, KAU OC 34 and KAU OC 35 were found best suited for biomass yield and essential oil content. Field experiments were conducted to assess the influence of growing condition (open and 50 per cent shade) and harvesting method (stage of harvest and height of harvest) on the performance of tulsi. Growing of tulsi at 50 per cent shade was superior to open condition with respect to fresh biomass yield and oil yield. However, eugenol content of tulsi was higher when grown under open condition. Further, harvesting of tulsi at 20 cm or 30 cm height from ground level at 75 and 135 DAT resulted in higher biomass yield, essential oil yield and total chlorophyll. In contrast, eugenol content was higher when plants were harvested at 20 or 30 cm height from ground level at 90 and 150 DAT. Tulsi extracts, shoot and root powders were evaluated for allelopathic effect on upland weeds and test crops (rice and cowpea). The results established the presence of allelochemicals in tulsi and phytotoxic activity on upland weeds and test crops (rice and cowpea). Incorporation of tulsi powder recorded greatest inhibitory effect, followed by aqueous extracts. Application of shoot and root powders of tulsi at 20 g/kg soil caused weed germination inhibition of 86.06 per cent and 79.56 per cent respectively in the first week. The powder form of shoot and root at 20 g/kg soil iii inhibited germination percentage of rice by 13.9 and 11.1 per cent and cowpea by 19.47and 16.67 per cent respectively. Evaluation of nematicidal action of tulsi against root-knot nematode (Meloidogyne incognita) proved significant effect of tulsi extracts on the mortality rate of second stage juveniles (J2s). The highest mortality of J2s was observed with aqueous extract of tulsi @ 30 per cent at all the periods of exposure such as 12, 24, 48 and 72 hours. Studies indicated the possibility of exploiting tulsi as a cheap and safe nematicide for the control of root-knot nematode.