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Pre-Flowering Harvesting of Ocimum gratissimum for Higher Essential Oil and Eugenol Yields Under Semi-Arid Tropics

Journal of Essential Oil Research: JEOR,  Mar/Apr 2005  by Kothari, Sushil K,  Bhattacharya, Arun K,  Singh, Kamla,  Ramesh, Srinivas I,  Et al

Abstract

In spice basil (Ocimum gratissimum L.), contribution of leaves, stalks and inflorescences were 59%, 23% and 18% to total plant biomass and 80%, 1% and 19% to total oil yield, respectively. The leaf oil was richer in eugenol but simultaneously had lower (E)-β-ocimene, compared to the inflorescence oil. Harvesting at pre-flowering produced 12.5%, 24.1%, 35.5% and 50.0% higher biomass yield compared to harvesting at 25%, 50%, 75% and 100% flowering, respectively, in the first year of cropping. The respective increase was 16.8%, 22.0%, 38.2% and 63.2% in the second year. Late harvested crop ( 100% flowering) contained the highest amount of essential oil and it decreased in the order of harvesting at 100% flowering > 75% flowering > 50% flowering > 25% flowering > pre-flowering treatment. The total oil yield was, however, significantly higher (15.8-19.9% and 12.7-33.6% in first and second years, respectively) with pre-flowering compared to all other harvest treatments. Pre-flowering harvested crop produced oil containing the highest amount of eugenol and it decreased in the order of harvesting at pre-flowering > 25% flowering > 50% flowering > 75% flowering > 100% flowering treatment.

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Key Word Index

Ocimum gratissimum, Lamiaceae, harvest management, oil yield, essential oil composition, eugenol, (E)-β-ocimene.

Introduction

The genus Ocimum (family: Lamiaceae), collectively called basil, consists of about 160 species (1), and is spread over the tropical, sub-tropical and wannerpart of the temperate regions of both the hemispheres ranging from sea level to 1800 ft altitude. Spice basil (O. gmtissimum L.), perennial and drought tolerant, is one of the important basil types and is cultivated in many Asian and Mediterranean countries and the United States. It is cultivated in about 2000 hectares in the northern and southern parts of India. Leaves and flowering tops of the plant yield an essential oil on steam distillation. The oil is used to flavor foods, dental and oral products, in fragrances and aromatherapy and in traditional rituals and medicines. Eugenol is the dominant constituent in the oil of O. grntissimum of the Indian (2-5), and Brazilian native plants (6,7) as against thymol and 1,8 cineole in Cameroon native plants (8), and thymol, γ-terpinene and pcymene in Togo and Benin native plants (9,10). Another rare chemotype rich in geraniol is also known to exist in East Africa (11). The oil of O. gratissimum of Indian and Brazilian origins being an important industrial source of eugenol, may replace pure eugenol in many pharmaceutical and cosmetic compositions.

Earlier, a large variability has been demonstrated in respect to composition of oil derived from leaf and inflorescence in O. tenuiflorum (12), O. basilicum (13), and O. micranthum (14). Similarly, changes in oil content and composition were observed with progressive stages of leaf development in O. tenuiflorum (15), plant height in O. basilicum (16), stage of crop harvest in O. basilicum (17), and O. gratissimum (17), and with season of harvest in O. gratissimum (4). There is, however, dearth of information on O. gratissimum in respect to yield and composition of oil obtained from different crop segments and as influenced by stage of crop harvest under semi-arid tropics.

Materials and Methods

Field experiments were conducted in 1999-2002 at the Research Farm of the Central Institute of Medicinal and Aromatic Plants, Resource Centre, Hyderabad (542 in above msl, 17°20' N and 78°3' E), India. The annual rainfall is about 760 mm of which 80% is received between June and September (southwest monsoon). The average temperature is 29°C, and varies from 22°-35°C, the highest (44°C day temperature) being in May and the lowest (12°C night temperature) in January. The winter season is characterized by mild, cool dry weather. The experimental location has a semi-arid tropical climate.

The soil of the experimental site was well drained, red sandyloam (alfic ustochrept) in texture, having organic carbon 0.3%, pH 7.3 and available N, P and K at 60.3, 9.5 and 142.5 kg/ha, respectively. Ocimurn gratissimum seeds were collected from cultivated fields in South India and six week old seedlings were transplanted in 10 x 20 m size plot in July 1999. Before final land preparation, neem cake (0.51 ha^sup -1^), phosphorus (40 kg P^sub 2^O^sub 5^/ha) and potassium (40 kg K^sub 2^O/ha) were applied and mixed well with the top soil of plot area. Nitrogen (60 kg N/ha) was applied into two equal split doses at 30 and 45 days after transplanting (DAT). At full bloom stage (77 DAT), observations were recorded on plant height and spread, number of branches and leaves/plant, leaf color (dorsal and ventral surface), shape, margin, length, width and size, inflorescence number/plant, color, diameter and length and flower color and diameter. On five randomly selected plants, apical part (25-35 cm) of all branches, including inflorescence, was harvested and whole herb weight/plant was recorded. Data were also recorded in respect of biomass distribution in leaf, stem and inflorescence. The oil content in leaf, stalk and inflorescence were separately determined along with whole herb (each three replications of 100 g each) following hydrodistillation in Clevenger-type apparatus for 4 h.

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