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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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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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