A Brief Perspective on Acacia a Member of Family Leguminosae

Tree members of the genus Acacia have benefits that are obvious for enhancing soil fertility in farming, forestry and agroforestry in regions with nutrient-poor soils, and for restoring degraded ecosystems and lands. Nevertheless, the species of the genus Acacia have got the potential to bring about significant adverse impacts on biodiversity or ecosystem functioning when it gets invasive. The ecology of the species in nearly all areas of its created range remains poorly understood. Here we have compiled the information regarding the importance, cultivation and the production of important species of genus Acacia. We hope this information will be useful to get awareness about the crucial trees in the genus Acacia.


Introduction
Acacia commonly called Acacias or Wattles is a common species found in dry, arid and semi-arid areas and also in the low-lying mountainous forest that belong to subfamily: Mimosoideae of the third-largest family Fabaceae (Pea family). It includes lianas, shrubs and towering trees. The term Acacias, given by Miller (1754) which come from an ancient Greek word 'Akakía' meaning "thorny Egyptian tree" or "Shittah tree (used in Hebrew Bible to refer trees wildly growing in Sinai desert and the Jordan valley, belonging to Vachellia (=Acacia) and Faidherbia genus)" attested before 1398. Akakía is a word of uncertain origin probably it is related to the Egyptian word 'Ake' meaning thorny or sharp point (Lewis and Short, 1879). Word' Wattle' was given by ancient tribe, Teutonic that means 'to weave' 1 . To date its complete actual origin of the name is unknown. Acacias are native to Australia and Africa which evolved as fire-resistant plants about twenty million years ago, with A. niloticaas the first species reported by Linnaeus.
The Wattle plant has more than 1350 species which can be broadly divided into two groups with 5 genera (early, there were 6) comprises of around 960 genera in Australia still retained the genus Acacia. One group of Acacias are having simple leaves containing Phyllodes (petiole develop into leaf-like appearance and function) with or without stipular spines. The second group has compound fern-like bipinnately dissected leaves with or without stipular spines and stem prickles, found in Australia, Africa and the USA. The plant starts spreading from these places to other countries where fire and dry conditions are prevalent. The plant started colonizing and began to The inflorescence is globulus cymose head of 10-13 mm diameter made up of hundreds of minutes, golden-yellow, prolific, campanulate penta-gamosepalous, penta-gamopetalous, polyandry (many, stalked, small), actinomorphic, ebracteate, sessile flowers on 2-3 cm peduncle with axillary or whorly in position. Flowers have monocarpous, superior, unilocular ovary. Pods are fleshy green when young and become black and hard at maturity, which is indehiscent. Pod dispersed through animals who brows on them. Seeds are 10-14 in number arranged in a single row which are smooth, areole (small bumps), sub-circular, blackish brown with 5.5-7.2 mm long and 5-5.7 mm wide. Their number ranges from 8,000 to 15,000 seeds per kg 7  It is a moderately-sized, gregarious, deciduous, thorny, perennial fast-growing tree (up to 10 years then show slow growth) found in the riverain area under arid areas, having peeling dark greyishbrown, thick, rough bark that peels off when mature with spreading elongated-feathery crown canopy, attaining a height up to 15 m. Bark is deeply cracked and flaking off in long, narrow, rectangular, vertical strips at maturity (which is a diagnostic feature), otherwise young plant has corky bark. Stems are slender, glabrous, shining, brownish-red, puberulous, small branchlets which are armed with false inconspicuous stipular spines present in pairs below the petioles with slightly infra axillary position and have no leaves on flowering branchlets, occasionally. Leaves are 4-9 mm long, subulate, stipulate, alternate, straight or hooked, bipinnate with 10-30 pairs of tiny, bluntended, pilose (small hairy) leaflets of 3-5 mm long. Between the first pair of leaves, large oval glands are present 8,9 . Thorns are shiny, stout, curved, reddish-brown, present in pairs of around 10 mm, present at the base of each leaf. The inflorescence is spiked (6-13 cm long) present in a cluster of 1-4, pedunculated with numerous tiny whitish-yellow, sessile, bracteate, cupular-campanulate calyx, polyandry, flowers. Calyx and petals are pale green. Stamens are long and brush-like, giving the colour of flowers 7 . The fruit is a flat pod of 10 cm long, thin, straight, irregular and sinuate along margins with pointed ends. Each pod are magenta when young, become dark golden-brown and dehiscent when mature that contain 4-7 seeds. Seeds are brown, orbicular or ovate but flat having 5-7 mm diameter.
It is a moderately-sized, thorny, deciduous tree, found in the hot dry forests, having, rough, yellowish-brown bark with an umbrella-like crown canopy of 20-25 m height. The plant has a twisted, stout and crooked trunk with several wide branches. Bark has pale-yellow patches (which is a diagnostic feature). Stems are erect, smooth, solid, greyish-white, rough, branched, slender and excorticating in irregular scale at maturity. Thorns present in pairs of 2-4 cm long, axial, straight, puberulous and brownish-red in colour.

A. farnesiana [syn. Vachellia farnesiana (L.) Wight et Arn./A. smallii Isely]
It is a small-sized, thorny, evergreen to a deciduous or semi-deciduous shrub or small tree, found in a tropical and sub-tropical area, having rough, light brown bark with the spreading canopy of 2-5 m height, usually of 7-9 m. Stems are slender, chocolatey-brownish-grey, hairless, spinescent, lenticellate, glabrous to purplish-grey, terete branches, generally show multiple trunks. Thorns are usually short, up to 1.5-1.8 cm long, ivory-white and present in pairs. Leaves are alternate, leathery, tomentose with 2-6 paired pinnae having 10-12 leaflets of 2-7 mm minute leaflets. The inflorescence is axillary pedunculate heads, scented, sessile, pentamerous, golden-yellow flowers and fruits are straight or curved, indehiscent pods of 4.6-7.2 cm long. Seeds are smooth, thick, chestnut-brown, elliptical which are embedded in a dry, spongy tissue of 7-8 mm long.

A. auriculiformis A. Cunn. ex Benth [syn. A. moniliformis Griseb]
It is a moderately-sized, fast-growing, crooked, evergreen, thorn-less tree, glaucous when young, generally cultivated, having grayish-white, vertically fissured, bark with drooping often multistemmed branches of 16-25 m height. Stems are erect, branched, initially smooth then become fissured with dense foliage. Leaves are alternate, simple and modified into phyllodes which are blade-like, pointed at both ends, coriaceous, and curved or sickle-shaped. The inflorescence is densely rigid spikes (7-9 cm) of yellowish-orange colour with loose, scented, long, campanulatecalyx, hermaphrodite, actinomorphic, complete flowers. The fruit is flat, glaucous, cartilaginous, oblong pods which become twisted at maturity. They have transversely veined with undulate margins which can have about 47,000 black shining seeds per kg. Seeds are transversely placed in the pods which are ovate to elliptical of 5-6 × 4-5 mm 10 .

Acacia plantation
Acacia plantation needs no particular nutrient and can grow on any type of well-drained soil with vey less watering (once in a week). Naturally, Acacia can grow on acidic, alkaline, dry and hot soil conditions. But, during cultivation soil can be mixed carefully with pine barks to avoid any type of rot or mulched with any other available material which can prevent drying out, at initial stages. For garden plantation, plantlets can grow in pots before increasing in the field and should not be kept for long because the roots become long, very quickly 11 . After seedlings developed in pots hole is dug twice the size of the pot and fill with water twice and allow it to drain away each time. Place the plantlets grown in pots in the hole fill it with soil and water at the end. Seedlings are planted at 2-3 m distance, and pruning is done each year after flowering to give the bushy appearance. For commercial purpose filed is of several hundred hectares, the following step are to be taken into consideration 12 .

Seed collection and preparedness
Seeds have shelf-life 6-8 months which are collected from mature and healthy trees, after the pods start cracking (best time for collection). Seeds are collected fromNovember to the end of January when they are green. This reduces the degree of pathogenicity during seedling growth. For judging the seeds whether they are healthy or not, leave the harvested pods to dry under sunlight for a day or so. If the pods remain turgid and turn dark, it would be a wise decision to collect the seeds.
On the other hand, if seeds lose their water in the pods and become flaccid, then reject those pods. They were washed under running water and with boiling water and allowed to cool for 24 hours at room temperature. If the seeds have to store either due to unavailability of suitable climate or limited nursery acclimatizing, then proper fumigation of the chamber and appropriate conditions should be given, and seeds are kept in either glass, plastic or tin moisture-proof jars. But the seeds should sow because the storage food becomes less due to respiration. It is advisable to treat the jars with some insecticidal powders. Generally, pyrethrin and benzene hexachloride based. Therefore, they are usually stored in dry, airtight containers. In several practices, the seeds of Acacia are treated by soaking into sulphuric acid 13 .

Nursery practices
It is essential to select the site of nursery construction, free from any type of soil-borne diseases or harmful fungi and nematodes or pests, to raise the seedlings. The sunlight availability should be fulfilled, and sandy, loamy drained soil should present, adequate irrigation and proper drainage system. Its location should be near-by where Acacia seedlings have to be planted on the fields and near the metal road. This inevitably reduces the impact of transportation shock to the seedlings and facilitate easy transport on roads, and also transport expense become less. Along with this, skilled labour should be satisfactory in the area. The area should not be flooded during the rainy season; enough level has to be maintained 14 . Raising the level of the nursery, protection against wind cane be sheltered by growing high canopy coverage trees. By this, excessive hotness during the day is also controlled. Proper weeding in the nursery should be done time-to-time, to stop secondary host pathogens and to decrease the water-use efficiency.

Sowing
Pretreated seeds are raised in a nursery, two seeds are sown at 1-2 cm depth in each container and within 3-4 days seedlings start growing. Generally, this step is done in the month of February when winters start ending. Soil is mixed with sand, farmyard manure and clay soil. Seedlings of around 25-35 cm plantlets are transferred to bags and planted in the fields. This pre-sowing treatment is necessary because the seed-coat is hard, which is impervious to water. They are now ready for transplant. No unique fertilization is required for seedlings Acacia. Pits of 0.5 ×0.5 ×0.5 m are dug before the start of rains.

Harvesting
Trees with girth of 70-110 cm are suitable for harvesting.

Weeding
In the arid zone, moisture content plays essential role for forestry. 6-8 weeks after planting, weeds usually start growing and this has to be planted-out. It is essential to uproot the weeds at the proper time before flowering. There is less chance of spreading of plant. Hoeing is done from time to time to prevent moisture loss and improve aeration.

Thinning and Pruning
For proper growth of plant pruning is done each year to give the bushy appearance.

Diseases
Several pests infest these trees and decrease their valuable products causing economic losses. So, it becomes necessary to recognize these pests and diseases and mitigate them in nurseries 16  Symptoms: initially yellowing of phyllode, thinning of crown, defoliation, dieback of branches, death of main branch of crown, development of epicormic shoots giving branchy appearance. Infection progresses, killing the epicormic shoots and ultimately the tree. Causative agent: Botryodoplodia theobromae Symptoms:appressed bark cracks, discoloured sapwood and dead with zonation lines, roots on the side of canker were dead with black zonation lines. The dead bark and tree parts are susceptible to termite infestation. Common name: Seed weevil Tissue damaged: pods and seed Effect: The adults lay eggs on the pods and then the larvae bore into the seed, often wholly destroying the seed and hence preventing germination.

Bruchidius uberatus
Common name: Seed beetle Tissue damaged: seeds Effect: The adults lay eggs on the pods, and the larvae bore into the seed, often completely destroying the seed and hence preventing germination.
Species affected: Acacia nilotica, A. catechu 6. Chrysobothris sp.   Symptoms: infestation causes no specific above-ground symptoms other than stunted growth, wilting and chlorosis. On the roots, we can find galls moderate to large which crush the xylem vessels, thus interrupting the water and minerals flow to the stem tissues.

Phytoplasma
Disease name: WITCHES BROOM Causal organism: Phytoplasma Species affected: A. mangium Symptoms: stunted growth, shape of phyllode is modified into needle like structure abnormally sprouting shoots which give the appearance of witches broom.

Conclusion
Forest plantations are actively playing a crucial role in the forestry market for each environmental and economic reasons. These forests are primarily placed to provide raw materials. Improvement through optimizing of silvicultural methods, exploring breeding and genetics of acacias is slowly going on. Although improvement remains slow, as when compared with crops, as a result of the era at blades' rotation, more significant tree dimension as well as substantial website management, a number of achievements in breeding and genetics of Acacias have provided a tremendous impact and benefit within the functional scale of forest industries.