Among the flowering plants that are valued by the aesthetic world for the beauty and fragrance of their flowers, Tuberose occupies an exclusive position because of its attractiveness, elegance and sweet pleasant fragrance. This bulbous plant is the source of Tuberose oil, an expensive commodity usually used in high grade perfumery. It is also cultivated for cut flowers, for bouquets and garlands. While the long flower spikes are excellent as cut flowers for table decoration, the individual florets are used for making garlands, floral ornaments, bouquets and buttonholes.
Tuberose is believed to have originated in Mexico or Central America. It is widely cultivated in Southern France and also in Morocco for the extraction of its natural flower oil. For many years, Tuberose flower oil has been one of the most valuable and expensive raw materials in perfumes.
Tuberose : Polyanthes tuberosa L. belongs to the family Amaryllidaceae. Tuberose is a half-hardy, herbaceous perennial, bulbous plant. It is classed as a monocotyledon, with leaves often light green in colour. It is an erect herb, 60-120 cms high with stout and short bulbs. Bulbs are made of scales, leaf bases and stem remains that are concealed within scales. Fibrous roots are mainly adventitious and shallow. Leaves are basal, 6-9 in number, 30 to 45 cms long, about 1.3 cms wide, linear with grass like foliage, bright green and reddish near the base. The foliage is narrow at the base and wide at the top and is arranged in a rosette. Tuberose inflorescences (spikes) bear 25 ± 10 pairs of florets that open acropetally (i.e., from base to the top of the spike). It is a cross pollinated crop. Polianthes genus contains three types of flowers. One of them is a single flower type having the basic chromosome number n = x = 30 and 2n = 60, which is female fertile; used in the perfumery industry and in breeding programs as a female parent. The other two are semi-double and double flower types and generally used as cut flowers. The flowers have a funnel shaped perianth and are fragrant, tubular and waxy white. About 25 mm long, the tube is bent only near the base, filaments are attached on upper part of the corolla, fragrant and in long terminal racemes. Stamens are six in number, ovary 3 locular and ovules numerous.
There are single as well as double flowered varieties. The single flowered type is mostly cultivated for the extraction of perfume while the double flowered variety is for the cut flower trade. The flowers on top of the long stalk are grouped in spike-shaped clusters 15 to 20 cms long. The flowering period begins in July reaching its maximum potential towards mid-August and lasting till the end of September when a secondary blooming takes place. There are four groups of cultivars of Tuberose.
(i) Single: most widely cultivated. Flower is pure white and has got a single row of corolla segments. E.g. 'Calcutta single', 'Mexican single', 'Rejat Rekha' and 'Suvarna Rekha'.
(ii) Double : Flowers are white, tinged with pinkish red. Petals are in several whorls. E.g. 'Pearl' and 'Calcutta double'.
(iii)Semi-double: Similar to double but with only 2-3 rows of corolla segments.
(iv) Variegated: This has got variegated leaves with yellow margins.
Although Tuberose can be grown under a variety of climatic conditions, a mild climate with an average temperature ranging between 20 ºC to 30º C is considered ideal. Loam and sandy loam soils having a pH range of 6.5 to 7.5 with good aeration and drainage are best suited for its cultivation. The plant is propagated by bulbs. Spindle shaped disease-free bulbs having a diameter of 1.5-3.0 cms are used for planting. Mother bulbs are preferred as they flower early. Finger or side bulbs take 2-3 years to flower. Of the 4 types of Tuberose, viz, single, double, semi-double and variegated, the single type has the maximum fragrance and is popularly used for the production of essential oil. The best time to plant is from May to July. The field is ploughed 2-3 times to bring the soil to a fine tilth. Well-rotten FYM at 20-30 t/ha is applied and mixed well. Furrows are opened 25-30 cms apart and bulbs are planted at 25 cms spacing in furrows. About 1.25 lakhs (800-900 kgs) of bulbs are required for a hectare of land. A fertilizer dosage of 100:200:200 kg N, P2O5, K2O/ha is generally recommended. Half the dose is applied basally and the other half as topdressing when the flower spikes start appearing. Weekly irrigation and regular weeding are required for a good yield. Thrips are known to attack the crop. The flowering season is between June and October. Flowers will be ready for harvest in 3-3.5 months’ time. Tuberose is harvested by cutting the fully opened spikes from the base during cooler hours of the day, either in the morning or evening. From a single crop, 2-3 ratoons are obtained. The average yield is around 5-10 tons/ha for planted crop, 9-12 tons/ha for the first ratoon and 4-6 tons/ha for each subsequent ratoon.
Post Harvest Technology
Tuberose flowers continue to develop their natural fragrance for some time after they have been harvested. The flower oil is extracted by enfleurage and solvent extraction with petroleum ether. Distillation cannot be employed as steam or water distillation of the Tuberose flowers directly results in very little yield of oil and sub-standard fragrance. Freshly picked flowers, before they open are enfleuraged. About 150 kgs of flowers yield 1 kg of absolute of enfleurage that contains 11-15% of steam volatile oil. Extraction of Tuberose flowers with petroleum ether yields about 0.08-0.14% of concrete. The concrete contains 3-6% of a steam volatile oil.