• Banana is a tall herb two to six metres high with milky juice in all the parts. It is monocarpic yet perennial, strongly tillering, monocotyledonous plant.

Root

• Purely adventitious, very shallow.

Underground stem

• The underground stem is the real stem called corm. Its growth is sympodial. The corm has short internodes.
• The bananas are clumped in habit, since suckers are produced from the corm.
• The buds are borne on the middle or upper part of the parent corm. The corm is covered with closely packed leaf scars.
• The corm's terminal growing point produces leaves in a spiral succession, in the axil of each leaf a bud is present.

Aerial system

• It is the pseudostem made up of a number of leaf sheaths completely encircling the axis of the stem.
• It is white in colour except where it emerges from the top. After being exposed to sunlight, it becomes green.

Leaves

• The leaves are spirally arranged and consist of a sheath, a petiole and a blade.
• The sheaths are nearly circular and tightly packed into non woody pseudostem which is functioning as the trunk of the plant. They are much longer than the blades.
• The petiole is rounded beneath and channeled above.
• In general, shape of the blade is blunt at the tip and tapered, rounded or even auriculate at the base. It is thickest near the mid rid and thinnest at the margins.
• The veins of the lamina are parallel with each other.

Inflorescence

• It is a terminal complex spike.
• Peduncle thick, glabrous or pubescent.
• Each spike in the inflorescence is subtended with big bracts.
• Bracts deciduous, crowded, spathaceous and spirally arranged. Bracts are lanceolate or broadly ovate, dark purple or brownish purple outside and pale puple or crimson inside.

Flowers

• Flowers are placed in the axils of the bracts, arranged biseriately and commonly number about to 12 to 20 per node.
• Basal flowers behave as pistillate flowers while the terminal ones as staminate. At the lower end, they form a bulbous male bud.
• The axis beyond the female phase is generally bare, but in some cultivars flowers and bracts are retained.
• The intermediate flower clusters are of transitional stage structure and are fuctionally male. Individual flowers are ebracteolate.

Perianth

• Strongly zygomorphic and is composed of two structures-a 5 number compound tepal and a free tepal, totally six tepals (Similar for pistillate and staminate flowers. In the 5 member, 3 outer major lobes + 2 minor inner lobes).
• Pistillate flowers - larger in size and have well developed ovaries. Stamens (5) reduced to staminodes. Ovary infereior and trilocular. Oblong ovules are two or more rowed in each locule in axile placentation. Style stiff and long, stigma club shaped and sticky.
• Staminate flowers - Stamens 5, long, filaments filiform, free anthers two lobed, linear basifixed, fertile pollen absent. The sixth stamen is also considered to be represented by free tepal of inner whorl-'tepalloid stamen'.

Floral biology

• The female and male flowers open by 6.30 a.m. to 8.00 a.m.
• The female flowers bear a well developed ovary which much exceeds the perianth in length and with a massive style, but their stamens are reduced to staminodes.
• In certain wild species of bananas, fertile stamens are present in the pistillate flower e.g. M. acuminata ssp banksii, M. schizocarpa (Here they can be considered as perfect flowers or functionally bisexual flowers).
• In male flowers, the ovary is abortive, the style and stigma are slender and anthers are well developed.

Fruit development

• In edible bananas, the fruit develops by vegetative parthenocarpy i.e. the ovary develops into a mass of edible pulp without the fertilization and even without the stimulus of pollination. So the fruits are seedless.
• In the bunch, each cluster is called hand and the individual fruit is called a finger.
• Fruit is a berry and has a leathery epicarp, slightly fibrous mesocarp, and fleshy endocarp.

Seed

• Abortive ovules, not visible in edible banana.

Plant

• The banana is a herbaceous perennial monocotyledonous plant with an underground corm.

Leaf

• The corm produces triangular scale leaves underground which leave scars marking the internodes.
• The growing point of a bud produces scale leaves underground and on breaking surface produces true leaves.
• Initially, leaves with narrow lamina are produced and at this stage the plant is called a 'sword sucker'.
• Gradually broad photosynthetic leaves are produced.
• The leaf sheaths are tightly packed together to form a pseudostem.
• The top of the sheath contracts into the petiole which is channeled on the upper surface and rounded below.
• Prior to emergence, the leaf is rolled around itself inside the pseudostem. The leaf unfurls in around 6-10 days after emergence.
• Depending upon the season of emergence, nutrition and stage of growth, leaf longevity varies from 35-165 days in the tropics.
• The time interval between emergence of successive leaves (phylacron) varies considerably and is reduced by low temperature, increasing plant age and is also affected by minerals.
• The total number of leaves produced varies and is affected by climate, nutrition and genomic constitution.
• Average new leaf emergence rate is 7 days in tropical conditions. Leaf emergence interval is shorter for acuminata and longer for balbisiana and hence varies in each variety based on its genomic constitution.
• Balbisiana genome favours larger leaf numbers in contrast to smaller numbers in acuminata.
• Balbisiana genome also favourably increases the leaf chlorophyll content.

Flower

• With regard to flowering, banana is day neutral, and unaffected by vernalisation.
• Flowering is determined entirely by age of the plant.
• Different approaches have been attempted to estimate occurrence of flowering.
• The assumption of a fixed number of leaves being produced prior to flower initiation has been shown to vary with variety and environment.
• The number of leaves remaining within the pseudostem seems fairly constant over a range of varieties and localities.
• Another approach known as the leaf function hypothesis involves computation of the product of leaf area, leaf longevity, temperature and daylight hours received by each leaf. But this has not been verified experimentally.
• A third hypothesis points to an interaction between corm and leaf in that though the function of the leaf system is important, the corm must have developed sufficiently to receive the flowering stimulus from the leaves.
• The number of functional leaves maintained on the plant influences shooting. Higher the number of functional leaves, earlier the shooting, early the bunch maturity and higher the bunch weight.
• The optimum number of functional leaves could be determined for each variety and used to judiciously harvest leaves.

Corm

• The true stem is the corm. It is sympodial and has very little horizontal growth.
• The corm bears fibrous roots on the lower portion and shoot buds on the middle and upper portions.
• It is the storehouse of nutrients.
• Internally the corm is differentiated into the central cylinder and the cortex.
• The growing point is the tip of an inverted cone and from this point are differentiated the leaves and aerial stem upwards and the corm downwards.

Roots

• Banana has a superficial and adventitious root system.
• Roots usually arise in groups of four at the surface of the corms central cylinder. Initially they are white and fleshy and later become somewhat corky.
• The number of roots can be quite high but root growth stops a month prior to shooting and subsequently senescence is rapid.
• Number of roots is affected by stage of growth, season and cultural practices.
• The roots spread upto 52cm laterally and 75cm deep but highest concentration of large roots (70%) is in the top 15cm zone.
• The numerous laterals of small diameter bear root hairs and are primarily responsible for nutrient and water uptake.

Sucker

• Sucker production is greatly influenced by ploidy level ie., diploids produce more number of suckers and with increasing ploidy level, sucker production decreases.
• Acuminata genome favours higher sucker production when compared to balbisiana genome.
• Within a given ploidy level, the girth of pseudostem, number of functional leaves, leaf area and leaf area duration, uptake of nutrients especially nitrogen and the number of developed buds as also the number of swollen buds on the corm at planting all positively influence sucker production.
• Corm weight or size and pseudostem girth had no relation to sucker production.
• Ethrel at 350ppm (3.5ml in 10 litres of water), sprayed at fortnightly intervals also increases sucker production.

Fruit

The edible bananas are vegetatively parthenocarpic ie., they develop a mass of edible pulp without pollination whereas pollination is essential for fruit development in wild-seeded types. The edible pulp (starchy parenchyma) which fills the fruit in parthenocarpic types and surrounds the seeds in seeded banana originates from the seeds The increase in bulk of the fruit is mainly due to cell enlargement.

• The growth pattern varies in pollinated and unpollinated banana fruits as revealed by volume. Seeded bananas show sigmoid and parthenocarpic types show non-sigmoid growth patterns.
• The growth rate is also related to ovule behaviour and seed content of fruit and ploidy.
• The growth curves are concave for edible acuminata clones, convex for bulbisiana and intermediate for hybrids.
• Increase in girth, volume and fresh and dry weights follow double sigmoid curve, though in case of increase in length the double sigmoid curve is not well defined.

Overall Plant growth and Development

Banana goes through three developmental phases viz., vegetative, floral and fruiting

• The first stage is marked by early vegetative phase and is sensitive to variation in mineral supply and the entire uptake of potash takes place during these first 3 months. This stage is crucial for later bunch development.
• The second stage, beginning at 6 months is marked by sudden contraction of the stem, (in the growing point, within the pseudostem) elongation of internodes, transition from foliage leaves to flower bearing bracts and functional differentiation between female and male flowers.The number of hands and fruits is determined at the later part of this stage and the climate during this period has a great effect on the fruit number.
• The third stage is marked by reduction of stem thickness, shortening of internodes, first fruit develops and female flower differentiation ceases giving way to male flowers. This stage partly determines the fruit size.

Yield contributing parameters

• The yield in banana ie., bunch weight is strongly influenced by pseudostem circumference and height at shooting.
• Total leaf area, number of fingers per bunch and weight of finger also greatly influence bunch weight.
• To a lesser extent, total number of leaves and sucker production also influences positively the yield.
• The time taken for shooting and harvest negatively influence bunch weight.

Growth pattern of banana

Age Growth phase

• 1^st month early vegetative phase, leaf production begins
• 2^nd month early vegetative phase, leaf production continues
• 3^rd month early vegetative phase, leaf production continues, sucker production begins
• 4^th month vegetative phase, leaf production continues, sucker production continues
• 5^th month vegetative phase, leaf production continues, sucker production continues
• 6^th month flower initiation, leaf production continues, sucker production continues
• 7^th month fruit differentiation, leaf production continues, sucker production continues
• 8^th month elongation of floral axis in early varieties, leaf production continues, sucker production continues
• 9^th month sucker production continues, leaf emergence stops and shooting in early varieties, leaf production continues, sucker production continues in late varieties
• 10^th month elongation of floral axis in late varieties, leaf production continues, sucker production continues in late varieties, in early varieties fruit filling i.e., starch accumulation, sucker production continues
• 11^th month leaf emergence stops and shooting of late varieties, sucker production continues in late varieties, in early varieties fruit filling continues sucker production continues
• 12^th month harvesting of early varieties, sucker production continues and fruit filling of late varieties
• 13^th month sucker production continues and fruit filling continues in late varieties
• 14^th month harvesting of late varieties.