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Essential oils extracted from basil (Ocimum spp.) by steam distillation are used to flavor foods, oral products, in fragrances, and in traditional medicines. The genus Ocimum contains around 30 species native to the tropics and subtropics, with some species naturalized and/or cultivated in temperate areas. Interand intraspecific hybridization have created significant confusion in the botanical systematics of this genus. Taxonomy of basil (O. basilicum) is also complicated by the existence of numerous varieties, cultivars, and chemotypes within the species that do not differ significantly in morphology. In this study we are using RAPD markers and volatile oil composition to characterize the genetic diversity among the most economically important Ocimum species. We hypothesize that the genetic similarity revealed by molecular markers will more accurately reflect the morphological and chemical differences in Ocimum than essential oil composition per se. Preliminary research using five Ocimum species, four undetermined species, and eight varieties of O. basilicum (a total of 19 accessions) generated 107 polymorphic fragments amplified with 19 primers. RAPDs are able to discriminate between Ocimum species, but show a high degree of similarity between O. basilicum varieties. The genetic distance between nine species and among 55 accessions within the species O. americanum, O. basilicum, O. campechianum, O. × citriodorum, O. gratissimum, O. kilimandscharium, O. minimum, O. selloi, and O. tenuiflorum will be analyzed by matrix of similarity and compared to the volatile oil profile. This research will for the first time apply molecular markers to characterize the genetic diversity of Ocimum associate with volatile oil constituent.

To determine the mode of inheritance of citral, linalool, methylchavicol, and methylcinnamate in basil, controlled crosses were made between chemotypes rich in each of these constituents. Four stable Ocimum basilicum populations selected for high methylcinnamate (79%), methylchavicol (95%), linalool (82%), and citral (65%) respectively, served as parents. Crosses were made using chemotypes rich in terpenes (linalool × citral), in phenylpropanoids (methylchavicol × methylcinnamate), and a third that combines chemotypes from both biosynthetic pathways (linalool × methylchavicol). True hybrids were selfed in isolation and one hundred F2 plants were analyzed for their oil composition. The parents, the F1 hybrids and the F2 generation of all plants were evaluated in a field trial under identical environmental conditions. Plants were harvested at full flowering, and dried at 380 °C. Identification of essential oil constituents were confirmed by GC/MS. The F2 segregation data for each major oil constituent trait will be examined by c2 analysis tests. Preliminary results indicate that methylcinnamate segregates in a 3:1 ratio, and is a dominant major gene. In the two crosses using methylcinnamate chemotype as a female parent, the F2 population segregates in 80:22 and 65:28 methylcinnamate:non-methylcinnamate plant types, with P = 0.42 and 0.25 and c2=0.64 and 1.29, respectively. Analysis of the other crosses are being processed, evaluating qualitative and quantitatively the presence or absence of each constituent in their F2 population.

Ocimum species are largely used in Brazil both as a condiment and in traditional medicine against bronchitis, cough, and sorethroat in the form of tea or syrup. As little research has examined the natural products from Brazilian basil, 14 accessions of Ocimum, including O. basilicum (4), O. campechianum (3), O. gratissimum (6), and O. kilimandsharicum (1), collected in Brazil were grown in the Purdue Univ. greenhouse and upon maturity harvested, the volatile oil extracted and analyzed by GC/MS. Thirty-one constituents were identified. Three accessions of O. gratissimum showed high content of eugenol (40% to 66%), while the other accessions contained either high thymol (33%) or p-cymene (28% to 42%). The constituents of the single O. kilimandscharicum included 1,8-cineole (39%), methyl-chavicol (21%), and ß-bisabolene (23%). O. campechianum accessions contained either high 1,8-cineole (62%) or high ß-caryophyllene (79%). O. basilicum could also be separated chemically: a linalool:methyl chavicol type (47:28%); one methyl chavicol type (72%), and a third, methyl cinnamate (61%). One accession was identified containing >90% trans-methyl cinnamate, which crystallized during extraction. Plants rich in targeted compounds, such as the one with 90% trans-methyl cinnamate, can be used as source of germplasm for breeding and potential commercialization