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Morphology > Growth >


Ikisan - Morphology of Sugarcane

Morphology

  • Sugarcane is a tall perennial plant growing erect even up to 5 or 6 metres.
  • The plant is composed of four principal parts, the root system, the stalk, the leaves and the inflorescence.

Root System

  • The root system is fibrous and consists of two types of roots, namely 'sett roots' and 'shoot roots'.
  • When sugarcane sett is planted in the soil and covered with moist soil, the root primordia (translucent dots) situated at the base of every cane joint is activated and produces roots.
  • These roots are known as 'sett roots' and are mostly temporary.
  • These are thin and much branched and function for a limited period. These roots provide moisture and nutrients for the growing primary shoot until it forms roots of its own. Later on these 'sett roots' cease to function and die.
  • After the emergence of the primary shoot from the bud, other roots are produced from lower rings of the lower nodes of the shoot.
  • Later, this process occurs progressively in upper rings of the nodes near the soil surface. Those formed first go downwards, whereas those formed near the soil
  • Surface roots grow in upper layer of soil for providing anchorage for the plant. These roots produced From shoot are known as 'shoot roots'.
  • These are permanent roots and are thick, fleshy and white in colour. New roots are continually produced from tillers.

Stalk

  • Known as "millable cane". It develops from the bud of another stem piece planted for vegetative propagation.
  • The stem pieces used for planting are known as "setts" which contains one or several buds. The bud sprouts under favourable conditions gives rise to a primary stalk from which secondary stalk, thus inducing tillering process.
  • Sugarcane stalk is composed of many distinct nodes and internodes. It is above ground portion of the plant which bears leaves and flowers.
  • A small portion of the stalk is below ground which is called as rootstock.
  • The node is the base of the leaf. At each node there is a bud, sometimes known as an 'eye' appearing on opposite sides of the cane. These buds are protected by the leaf sheath, which is folded tightly around the internode. Buds are presented in a longitudinal groove. Buds are shell shaped. On the tip of the bud a germination pore is present through which the sprouting shoot emerges.
  • The nodes have (i) root band with primordial root (ii) bud which is characterstic to each variety (iii) a wax band below the node and (iv) a growth ring above the node.
  • Immediately above each node, two or three translucent dot like structures known as root primordia appear in root band. These root primordia give rise to 'sett roots' as indicated earlier.
  • Just below the bud is a raised portion known as the leaf scar.
  • The internodes vary in shape, length and thickness depending upon the variety and growth conditions.
  • Various internode shapes are-cylindrical, tumscent, bobbin shaped conoidal, of conoidal and curved.
  • Sugarcane produces branches that grow from below the surface of the soil.
  • The under ground portion of the stem tapers rapidly and from the lateral buds of this region the shoots develop. These are called tillers.
  • Single cane may produce as many as 20 to 40 tillers depending upon variety and environmental conditions.

Leaves

  • The leaves of the cane plant grow alternately on opposite sides of the cane stalk from the nodes.
  • Leaf of sugarcane consists of a sheath and the blade with the ligule in between. The sheath is attached to the stalk by a basal ring and completely clasps the stalk. It is normally a light green in colour. The outer surface of sheath is often hairy.
  • The leaf blade is long, flat structure varying from one to one and a half metres in length and 5 to 7 centimetre wide.
  • The colour of blade varies from yellowish-green to very dark green depending on both the variety and nutritional status of the plant
  • The midrib is prominent with a groove on the upper surface.
  • The leaf edges are generally serrated.
  • The projection from the leaf sheath near the blade joint is the auricle, which does not occur in some of the varieties.
  • At the junction of the sheath and blade there is a membraneous attachment known as the ligule which bears long hairs.

Sheath

  • Green with red blotches;
  • moderate to heavy bloom;
  • scarious border prominent;
  • sheath splitting occasional Clasping
  • Spines present on the middle of the sheath;
  • deciduous.

Blade Joint

  • Transverse Mark: Purplish green; medium: fair bloom. Ligule: Medium; Crescentiform; symmetrical; gradually tapering towards the edges. Ligular Process: Indicated on one side.

Arrangement

  • Number: Abundant. Carriage: Younger leaves droop from top one third and older leaves droop from the middle. Top : open.

Inflorescence

  • The inflorescence of a sugarcane generally called the 'arrow' is an open panicle. It is long (30 centimetre or more) and tapering.
  • The arrangement of the spikelets is racemose, that is, the oldest flowers are at the bottom and the youngest at the top.
  • The flowers open in succession over a number of days.
  • Flowers have both male and female organs, but not all produce fertile pollen.
  • Some of the varieties have fertile pollens but they are usually small and low vitality. Sugarcane usually flower at the age of ten. to twelve months, but some varieties in north India do not flower at all. Due to this fact cane has so long been propagated vegetatively by cuttings of sugarcane. Cane produced from seed is not so vigorous, but it is important for breeders.

Cane

  • Medium-thick; slightly staggered; slightly oval in cross section, internal tissue yellow with purple tinge: rind hard; pith present as small cavity.
  • Yellowish green with purple tinge; turning dark green on exposure having red blotches; growth ring greenish yellow, root zone purplish yellow.
  • Cylindrical with a tendency to become conoidal; splits present; ivory markings present; weather markings present; bud groove rather distinct; moderate bloom throughout. Wax Band: Medium; constricted often merges with the general bloom. Growth Ring: Medium; slightly swollen; occasionally the growth ring width and root zone width ale found to be almost equal. Root Zone: Narrow; slightly constricted; generally has two rows of staggered root eyes.

Node

  • Slightly depressed; leaf scar slightly inclned.

Bud

  • Medium, plumpy, ovate; occasionally hairs at the tip of the bud noticed; inserted at leaf scar. Flange : Not prominent; arising from bottom one third. Venation and Germpore : Nerves more; running parallel; converging at the tip; germination apical.

 
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Ikisan - Growth Phases of Sugarcane

Growth phases

  • Sugarcane is a C4 plant having high efficiency in storing solar energy and most efficient converter of solar energy, thus having potential to produce huge amounts of biomass.
  • Sugarcane has essentially four growth phases, though it is difficult to recognise distinct duration of each.
  • The growth phases are

    1. Germination phase,
    2. Tillering phase,
    3. Grand growth phase,
    4. Maturity and ripening phase.

Germination phase

  • The germination phase is from planting to the completion of germination of buds.
  • Under field conditions germination starts from 7 to 10 days and usually lasts for about 30-35 days.
  • In sugarcane, germination denotes activation and subsequent sprouting of the vegetative bud.
  • The germination of bud is influenced by the external as well as internal factors.
  • The external factors are the soil moisture, soil temperature and aeration.
  • The internal factors are the bud health, sett moisture, sett reducing sugar content and sett nutrient status.
  • Optimum temperature for sprouting is around 28-300 C.
  • The absolute lowest temperature for germination is about 120 C. Warm, moist soil ensures rapid germination.
  • Germination results in an increased respiration and hence good soil aeration is important.
  • Therefore open structured porous soils facilitate better germination.
  • Under field conditions, about 60 per cent germination can be considered safe for raising a satisfactory crop.

Tillering phase

  • Tillering starts from around 45 days and may last upto 120 days of the crop.
  • Tillering provides the crop with appropriate number of stalks required for a good yield.
  • It is influenced by various factors such as variety, light, temperature, irrigation (soil moisture) and fertilizer practices.
  • Light is the most important external factor influencing tillering.
  • Adequate light reaching the base of the sugarcane plant during the tillering period is of paramount importance.
  • Around 300 C temperature is considered optimum for tillering. Temperature below 200 C retard tillering.
  • Tillering is a physiological process of repeated underground branching from compact nodal joints of the primary shoot.
  • Usually early formed tillers give rise to thicker and heavier stalks.
  • Late formed tillers either die or remain short or immature.
  • Maximum tiller population reaches around 90-120 days of the crop.
  • By about 150-180 days, atleast 50 per cent of the shoots die and a stable population is established.
  • Cultivation practices such as spacing, time of manuring, availability of water and weed control influence tillering.
  • Though 6-8 tillers are produced from a bud, ultimately only 1.5 to 2 tillers per bud remains to form canes.
  • Ratoon crop gives much higher and early tillering than a plant crop.
  • Encouraging good tillering is important to build adequate population.

Grand growth phase

  • Out of the tillers produced, as already stated, only about 40-50 per cent survive to form millable canes by around 120-150 days.
  • Then onwards, the stalks grow rapidly almost at the rate of 4-5 internodes per month under favourable conditions.
  • The cane elongation is facilitated by availability of adequate water, fertilizers and warm and sunny climatic conditions.
  • Under moisture stress shorter internodes are formed.
  • The grand growth phase lasts upto 270 days in a 12 month variety.
  • This is the most important phase of the crop wherein the actual cane formation and elongation and thus yield build up takes place.
  • Warm and humid weather conditions favour better cane growth.
  • A temperature around 300 C with a humidity of around 80 per cent is most conducive for good growth.
  • During this phase leaf production and their growth is frequent and rapid.
  • A well grown crop may reach a leaf area index (LAI) of around 7-8.

Maturity and ripening phase

  • Maturation and ripening phase or sucrose synthesis and accumulation phase lasts for about 3 months.
  • The period between 270 to 360 days may be considered as maturity and ripening phase.
  • During this phase rapid accumulation of sugar takes place and vegetative growth is reduced.
  • As ripening advances, simple sugars (monosaccharides viz., fructose, glucose) are converted into cane sugar (sucrose, a disaccharide).
  • Cane ripening proceeds from bottom to top and hence bottom partion contains more sugars thatn the top protions.
  • Ample sunshine, clear skies, cool nights and warm days (i.e., more diurnal variation in temperature) and dry weather are highly conditions for ripening.
  • In the country, highly favaurable conditions for ripening are found in certain parts of Maharashtra, northern Karnataka and South Gujarat.
  • This is why Maharashtra records best recoveries of sugar in the country.

Composition of Sugarcane

  • At harvest, of the total above ground dry biomass, sugarcane stalks account for about 75% and the leaves and tops around 25%.
  • A ripe sugarcane of 12 months duration will have around 16% fibre, 80% absolute juice and ash and other colloids in small proportions.

 
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