Botanical features of Pongamia
Pongamia tree is indigenous to the Indian subcontinent and south-east Asia. The tree grows abundantly along the coasts and riverbanks in Myanmar. It has been successfully introduced to humid tropical regions of the world as well as parts of Australia, New Zealand, China and the USA.
Distribution in India:
The tree grows well in wastelands of Karnataka, Andhra Pradesh, Tamil Nadu, Maharashtra, Orissa. The tree is found almost throughout India.
Commonly known as Indian Beach Tree, Honge, Karanja Ponge, Kanaga.
Botanical description of Pongamia pinnata
Pongamia is often grown as avenue tree nearly all over India. It resists drought well, moderately frost hardy and highly tolerant to salinity. The tree is used for afforestation, especially in watersheds, in drier parts of the country and also in social forestry plantations. P. pinnata is a plant well-suited to “marginal lands”. Growth is seen best from sea level to an altitude of approximately 1,200 m and an optimal annual rainfall of 500 to 2,500 mm. It is found growing under temperature of 28 °C to 40 °C. It is found growing mainly in red soil and few in black soil.
Pongamia pinnata is a legume which shows tap root system with formation of nodules resulting from a symbiotic relationship with nitrogen-fixing bacteria. Previous studies on the nodulation in pongamia showed the presence of endogenous rhizobium species and their ability to nodulate.
It is a medium sized glabrous tree, with a short bole and spreading crown and stem girth of more than 20 cm to 250 cm. Bark is greyish green, turns brown on subsequent growth and attains smooth or rough surface. The branching begins to grow above the ground level from 5ft to 7ft. The trunk has primary and secondary branches. The primary branches range from 2 to 4 numbers.
Leaves are imparipinnate, leaflets are ovate or elliptic in shape and ranging from 5-7 nos. Leaves are 5-10 cm long 4-6 cm wide and pointed at the tip.
Flowering begins during the month of March to May of a well established tree of age group 4-5yrs. The flowers resemble a typical legume flower. Flowers are white, pink to lilac in colour. They arise in a allixary raceme position with two keel and two wing petals, and a single standard petal. Insect mediated pollination is observed most often by bees. Abundant pollen is released from flowers mainly in the keel petals triggered by the nectar feeding bees. Mature flowers usually open for 24 hrs with coinciding of the nectar release at the same time. The nectar contains up to 60 % sugar principally glucose, fructose, sucrose.
Formation and development of fruits:
Fruits are referred to as pod in pongamia. Fruiting is usually observed during the month of June. The number of fruits per bunch ranges from 5-6 to 10-15 in number. Fruits begin to develop after fertilization of flower. The developmental stage of the pod is divided into three – light green, half brown and dark brown stage. Pods develop to maximum size from the month of June to September. The embryo consists of pair of cotyledons. Accumulation of the storage components in the cotyledon begins from October and stabilizes at the end of maturity which coincides with the harvesting period.
The mature pods are brown in colour, woody, indehiscent. The tip of the pod is usually mucronate or beaked. The surface of the pods and seeds is either rough or smooth. The pods are varying in size (small, medium, large).
Tree improvement program in general includes germplasm collection, maintenance, evaluation of the germpalsm for eliteness, establishment of clonal orchards, hybridization program.
Germpalsm collection, maintenance and evaluation:
Pongamia candidate plus trees may be marked along the wastelands, bunds, roadside, canal side, farmbund, backyards in villages for germplasm collection. Selection is preferred on the basis of 1km-5km separation between the trees within the same area. Trees aged above 7yrs should be selected. Pods should be collected from all sides of the tree to ensure uniformity. The yield performance of the trees should be recorded. These CPTs may be subjected to evaluation of certain morphometric traits like tree height, girth at breast height (GBH), number of main branches and sub-branches, canopy diameter and shape, branching pattern, fruits per bunch, average seed yield per tree. The pod characters like pod size, thickness, pod tip, pod texture may be recorded. The oil content of the seeds from these candidate plus trees should be analysed. Seeds from these candidate plus trees should be germinated in the nursery and seedlings to be raised and maintained. Grafts from these trees should be maintained. The germplasm thus collected should be carefully maintained under proper nursery conditions for further studies. The marked candidate plus trees should be studied for seed yield and oil content for three successive years for confirmation. Superior genetic material with respect to seed yield and oil content could be identified from the existing population based on proper selection procedure.
Establishment of clonal orchards:
The base populations of candidate plus trees could be used for establishment of clonal orchards in selected geographical zones of different states and progeny studies of these pongamia trees can be conducted. Clonal orchards can be further utilized for bulk seed collection and biodiesel production.
Among many species identified as promising substitute for fossil fuel, Pongamia pinnata is distributed widely in different agro-ecological zones of India. In Karnataka different zones have been identified as suitable habitat for high population of pongamia trees. The tree grows well in northern dry zone, central dry zone, eastern dry zone, southern dry and transition zone of Karnataka. Other dry zones of Andhra Pradesh, Tamil Nadu, Orissa and Maharashtra have also been identified for growing pongamia trees.
Generally seeds do not required any pretreatment before sowing. Maximum germination can be obtained if freshly harvested seeds are used for sowing. Germination percent start reducing after three months from the data & harvest. Soaking the seeds in water for 6 hrs improves germination present and vigour. Seeds are sown in seed beds / polybags / sand tray with micropyle facing down wards. Seeds germinate within two weeks of sowing.
Establishment of seedlings, weeding and intercropping:
Seedlings attain a height of 25-30 cm in their first growing season. Transplanting to the main field should be done at the beginning of the next rainy season when seedlings are 60 cm in height. The field should be cleaned and pitting will be done before starting of monsoon. Pit sizes of 45cm x 45 cm x45cm are appropriate for planting in a plantation scale with a space of 5 m x 5 m. The pit should be filled in the 1:2:1 sand soil and farm yard manure before planting. Soil should be retained around the roots during transplanting. In the first two years of establishment, during the summer, necessary irrigation is adopted. Furthermore, the long-term viability of tree crop species such as P. pinnata is dependent on good pruning management practices. Pongamia seedlings withstand shade very well and can be inter-planted in existing tree stand. Pongamia starts yielding from 6th year onwards. If grafted seedlings are planted, it starts bearing from 4th year.
Despite the success in germination of the seeds, development of techniques for propagation of superior genotypes is required for mass propogation. Successful studies on development of adventitious roots in shoot cuttings have been reported. Indole acetic acid (IAA), indole butyric acid (IBA) and naphthyl acetic acid (NAA) have been reported as effective root inducers. Pongamia is easily established by direct seedling or by planting nursery raised seedling propagation by branch cutting and root suckers is also possible. Wedge grafting of superior genotypes have been standardized.
Pest and disease
The world agroforestry centre has reported the infestation of pests and fungal disease in Pongamia. Parnara mathias, Gracillaria spp., Indarbela quadrinotata, Myllocerus curvicornis, and Acrocercops spp are few pests infecting the plant, Ganoderma lucidum and Fomes merilli are fungal pathogens identified in root and shoot tissues. These pests and fungal pathogens can be controlled by using pesticides and fungicides respectively. Leaf galls, fruit galls and fruit borers have been identified.
Previous reports on phytochemical investigation of Pongamia pinnata indicated the presence of abundant prenylated flavonoids such as furanoflavones, furanoflavonols, chromenoflavones, furanochalcones and pyranochalcones. Karangin, pongamol, pongagalabrone and pongapin, pinnatin and kanjone have been isolated and characterized from seeds.
Pongamia is a multipurpose tree. The different parts of the tree are used for medicine, fuel, manure, fodder.
It is also used in Ayurvedic and Sidda medicine systems of India. Traditionally leaf is used as antidiarrheal, leaf extract as antihyperammonenic, seeds showed antihelmintic activity activity, seed extract showed antiviral activity, extract of flowers showed antihyperglycemic and antilipidperoxidative effect. Oil showed antibacterial and antifungal activity. Karanjin has been reported to possess potent anti-scabies and anti-leprotic activity.
Wood is yellow, white and coarse textured, it is moderately strong light widely used for bullock cart, farm implements, furniture, commonly used a fuel wood.
Leaves are popular as green manure for rice, sugarcane fields, areca gardens, coffee plantations. Leaves with seed powder showed mosquito repellant activity. It has positive effect on soil N, P and K, mycorrhizal formation, nodulation in legumes.
The oil is used for leather dressing, soap making, lubrication, and illumination purposes. After trans-esterification oil is used as biodiesel in diesel engines.
Pongamia oil and biodiesel
It has high nitrogen content and used as efficient organic fertilizer for crop plants. The detoxified oil cake has been incorporated with animal feed successfully. The manurial value of the press cake is as follows nitrogen (5.1); phosphorus (1.1), sodium (0.8) and potassium (1.3).