Unit 2: Production Technology of Tropical Fruits - Subjective Questions

Climatic requirements:

• Mango is a tropical and subtropical fruit crop that grows well at temperatures between and .
• A cool and dry period before flowering promotes flower-bud differentiation.
• Dry weather during flowering and fruit development favors good fruit set and reduces disease incidence.
• Rain, fog, or high humidity during flowering may encourage anthracnose and powdery mildew.
• Hot winds and frost can damage young plants, flowers, and developing fruits.

Soil requirements:

• Mango can grow in a wide range of soils, but deep, well-drained loam is preferred.
• The soil should have a depth of at least 2 m for proper root development.
• A soil pH of approximately 5.5-7.5 is suitable.
• Waterlogged, highly saline, and strongly alkaline soils should be avoided.
• Soils with good moisture-holding capacity and adequate organic matter support better growth and productivity.

Mango is commercially propagated through vegetative methods because seedlings are highly variable and have a long juvenile period.

Important propagation methods:

• Veneer grafting
• Stone or epicotyl grafting
• Softwood grafting
• Inarching

Procedure of veneer grafting:

1. Select a healthy seedling rootstock about one year old.
2. Make a shallow downward cut of about on the rootstock and remove a thin slice of wood and bark.
3. Prepare a matching wedge-shaped cut on a mature scion stick taken from a selected mother plant.
4. Insert the scion into the prepared cut so that the cambial layers of scion and stock coincide on at least one side.
5. Tie the graft firmly with a polyethylene strip to prevent drying and movement.
6. Remove the rootstock above the graft union after the scion starts growing.
7. Remove shoots arising below the graft union and harden the graft before field planting.

Veneer grafting is preferred because it is simple, economical, and produces true-to-type plants.

Planting systems:

• The square system is most common because it facilitates intercultural operations in both directions.
• The rectangular, hexagonal, and contour systems may be adopted according to field shape and topography.
• High-density planting is used with compact cultivars and systematic canopy management.

Spacing:

• Traditional orchards generally use a spacing of about .
• Moderately vigorous cultivars may be planted at .
• High-density orchards may use closer spacing such as , depending on cultivar, climate, and training practices.

Canopy management:

• Train young trees to develop 3-4 well-spaced scaffold branches in different directions.
• Remove rootstock sprouts, dead branches, diseased shoots, and crossing limbs.
• Prune overcrowded branches after harvest to improve light penetration and aeration.
• Control tree height and canopy spread in high-density orchards through regular heading-back and thinning.
• Avoid excessive pruning because mango bears mainly on mature terminal shoots.

Proper canopy management improves spray penetration, fruit color, yield efficiency, and ease of harvesting.

Alternate bearing:

Alternate bearing is the tendency of a mango tree to produce a heavy crop in one year, called the on-year, followed by a poor crop in the next year, called the off-year.

Contributing factors:

• Cultivar characteristics
• Exhaustion of food reserves after a heavy crop
• Inadequate vegetative growth after harvest
• Hormonal imbalance and unfavorable weather
• Poor nutrition and orchard management

Management:

• Plant regular-bearing cultivars suitable for the region.
• Maintain balanced nutrition, irrigation, and post-harvest care.
• Thin excessive flowers or fruits during heavy-bearing years where feasible.
• Apply recommended growth regulators only according to locally validated schedules.
• Prune after harvest to encourage healthy, synchronized shoots.

Mango malformation:

Malformation produces compact, abnormal vegetative shoots or crowded flower clusters with shortened axes. Floral malformation causes poor fruit set and serious yield loss.

Management:

• Use healthy planting material and tolerant cultivars.
• Remove malformed shoots or panicles with of healthy tissue below the affected portion.
• Destroy removed material away from the orchard.
• Avoid excessive nitrogen application.
• Follow recommended acaricide, fungicide, and growth-regulator measures where the causal complex and local extension recommendations justify them.

Maturity indices:

• Shoulders become full and rise above the point of stalk attachment.
• Peel color changes from dark green to light green in many cultivars.
• The pulp changes from white to cream or yellow.
• The stone becomes hard and the specific gravity generally increases.
• Days from fruit set, heat units, and dry matter may also be used for particular cultivars.

Harvesting:

• Fruits should be harvested at physiological maturity but before full ripening.
• Use a mango harvester or clipper and retain a short stalk to reduce sap injury.
• Avoid shaking the tree or allowing fruits to fall.
• Harvest during cool, dry hours and protect fruits from direct sunlight.

Post-harvest handling:

• De-sap fruits by placing them stalk-end downward on racks.
• Sort and grade according to size, maturity, freedom from defects, and cultivar.
• Wash and apply approved hot-water or disease-control treatments where required.
• Pack fruits in ventilated corrugated fiberboard boxes with suitable cushioning.
• Pre-cool and store at a cultivar-appropriate temperature, avoiding chilling injury.
• Use approved uniform-ripening procedures and never use unsafe ripening chemicals.

Edible bananas originated mainly from Musa acuminata and Musa balbisiana.

• The symbol A represents the genome contributed by Musa acuminata.
• The symbol B represents the genome contributed by Musa balbisiana.

Major genomic groups:

• AA and AAA: Predominantly dessert bananas. They generally possess sweet pulp, good eating quality, and varying degrees of susceptibility to drought and diseases.
• AAB: Includes many dessert and plantain types. These have two A genomes and one B genome and often show good fruit quality with some hardiness.
• ABB: Commonly includes cooking bananas. The stronger B-genome influence generally contributes vigor, drought tolerance, and starchy fruits.
• AB and BB: Less common among major commercial edible cultivars.

Significance:

Genome classification helps explain plant vigor, fruit use, hardiness, disease response, and breeding relationships. Most commercial bananas are triploid and parthenocarpic, producing seedless fruits without normal fertilization.

Banana is propagated vegetatively because commercial cultivars are generally seedless.

Propagation by suckers:

• Sword suckers are preferred because they have narrow leaves, a strong connection with the mother corm, and vigorous growth.
• Water suckers with broad leaves and weak corms are less desirable.
• Select healthy, pest-free suckers of uniform size.
• Trim roots and decayed tissue, pare the corm carefully, and apply recommended sanitation treatments before planting.

Tissue-culture plants:

• Plants should come from an accredited source and be true to type.
• They must be properly rooted, hardened, uniform, and free from visible pests and diseases.
• Tissue-culture plants support uniform growth and harvesting but require careful early irrigation and management.

Planting:

• Prepare pits or furrows according to soil and irrigation method.
• Incorporate well-decomposed organic manure and recommended basal nutrients.
• Plant at the onset of favorable weather or whenever assured irrigation is available.
• Common spacing ranges from about to , depending on cultivar and system.
• Plant at the proper depth, firm the soil, irrigate immediately, and replace casualties promptly.

Banana is a heavy feeder and requires continuous moisture because of its rapid growth and shallow root system.

Nutrient management:

• Apply well-decomposed farmyard manure or compost during land preparation.
• Base fertilizer rates on soil testing, cultivar, planting density, and expected yield.
• Apply nitrogen and potassium in split doses during vegetative growth and bunch development.
• Supply phosphorus mainly as a basal or early application.
• Correct deficiencies of micronutrients such as zinc, boron, magnesium, or iron only after diagnosis.
• Fertigation improves nutrient-use efficiency under drip irrigation.

Water management:

• Maintain uniform soil moisture without waterlogging.
• Drip irrigation is preferred because it saves water and supports fertigation.
• Increase attention to irrigation during hot weather and bunch development.
• Mulching conserves moisture and suppresses weeds.

Intercultural operations:

• Remove unwanted suckers regularly, retaining only the follower needed for ratooning.
• Carry out shallow weeding to avoid root injury.
• Earth up plants to improve anchorage and drainage.
• Remove dry and severely diseased leaves without damaging functional foliage.
• Maintain field sanitation and adequate drainage throughout the crop cycle.

Propping:

Propping is the support of bearing banana plants with bamboo poles, wooden props, or suitable supports. It prevents lodging and pseudostem breakage caused by heavy bunches or strong winds.

Desuckering:

Desuckering is the periodic removal of unwanted suckers. It prevents competition for water, nutrients, and light. In a ratoon system, one healthy follower may be retained at the correct stage and position.

Denavelling:

Denavelling is the removal of the male bud after the last functional female hand has set. It may improve sanitation, reduce unnecessary nutrient use, and facilitate bunch management. It must be timed correctly to avoid injury.

Bunch covering:

The bunch is covered with a perforated protective sleeve after fruit set. Covering:

• Protects fruits from rubbing, dust, sun scorch, and minor insect injury.
• Produces a more uniform microclimate around the bunch.
• Improves peel appearance and market quality.
• May advance maturity under suitable conditions.

These operations improve crop uniformity, reduce physical damage, and increase the proportion of marketable fruits.

Maturity standards:

• Fingers become full and less angular.
• Floral remnants at the fruit tips dry and fall easily.
• Peel color changes from deep green to a lighter green.
• Fruit age after shooting and the pulp-to-peel ratio may be used for precise harvest scheduling.
• Maturity stage should match transport distance and market requirements.

Harvesting:

• Support the bunch and cut the pseudostem partially so that the bunch lowers gently.
• Cut the bunch with a padded knife and avoid impact and latex staining.
• Carry bunches on padded supports to the packing area.

Post-harvest operations:

• Separate hands, trim crowns, wash, sanitize where approved, and grade fruits.
• Pack in ventilated cartons with protective liners or cushioning.
• Remove field heat before transport.

Ripening:

• Bananas are climacteric fruits and can be ripened with controlled ethylene exposure.
• Temperature, humidity, ventilation, and ethylene concentration must be regulated in a ripening chamber.
• Calcium carbide is unsafe and should not be used.

Storage:

• Store mature-green bananas under recommended temperature and high relative humidity.
• Avoid excessively low temperatures because they cause chilling injury, poor color development, and abnormal ripening.

Climatic requirements:

• Papaya is a tropical crop that performs best under warm conditions, generally around .
• It requires abundant sunlight for rapid growth and high fruit quality.
• Strong winds can uproot plants or break their soft, hollow stems.
• Very high or low temperatures may interfere with flower expression, pollination, and fruit shape.

Soil requirements:

• Deep, fertile, well-drained sandy loam or loam is ideal.
• A soil pH of about 5.5-7.0 is generally suitable.
• The soil should be rich in organic matter but free from stagnant water.

Effect of waterlogging:

• Papaya has a sensitive root system and soft stem base.
• Poor aeration under waterlogged conditions causes root decay and encourages collar and root-rot pathogens.
• Even short periods of standing water can result in yellowing, wilting, and plant death.

Effect of frost:

• Papaya tissues contain considerable water and are highly susceptible to freezing injury.
• Frost damages leaves, growing points, flowers, and fruits and may kill the entire plant.

Raised beds, drainage channels, windbreaks, and selection of frost-free sites are therefore important.

Papaya commonly exhibits three sex forms:

• Male plants: Bear long, pendulous inflorescences with predominantly staminate flowers and normally produce little or no commercial fruit.
• Female plants: Bear pistillate flowers close to the stem. They require compatible pollen and often produce rounder fruits.
• Hermaphrodite plants: Bear bisexual flowers and can self-pollinate. They commonly produce elongated fruits preferred in many markets.

Effect on orchard establishment:

• In dioecious populations, several seedlings may initially be planted per pit because sex cannot always be identified reliably at the nursery stage.
• After flowering, excess plants are removed while retaining females and sufficient male plants for pollination.
• A commonly followed principle is to retain approximately one healthy male plant for every 10-15 female plants, adjusted for cultivar and field conditions.
• In gynodioecious cultivars, female and hermaphrodite plants occur, and hermaphrodites are often retained for their fruit shape and self-pollination.

Effect on production:

Sex expression influences pollination, fruit set, fruit shape, seed content, and marketability. Temperature and genetic factors can also affect floral form, causing malformed or sterile flowers under unfavorable conditions.

Seed extraction and treatment:

1. Select fully ripe, healthy fruits from true-to-type, high-yielding plants.
2. Extract the seeds and remove the gelatinous sarcotesta by rubbing and washing.
3. Dry the cleaned seeds in shade.
4. Treat seeds with an approved biological or chemical protectant where recommended.

Nursery raising:

• Sow seeds in sterilized nursery beds, trays, or polyethylene bags containing a porous medium.
• Place seeds at a shallow depth and maintain uniform moisture without overwatering.
• Protect seedlings from damping-off, intense rain, and excessive shade.
• Retain healthy, vigorous seedlings and harden them before transplanting.

Transplanting and establishment:

• Transplant seedlings when they are young and actively growing, usually with several true leaves.
• Avoid root disturbance because papaya responds poorly to severe transplant shock.
• Plant in well-drained pits or on raised beds at spacing suited to the cultivar, commonly around or .
• In populations where sex is uncertain, plant multiple seedlings per pit and thin them after flowering.
• Irrigate immediately, provide temporary shade if necessary, fill gaps, and protect plants from wind and standing water.

Papaya ring spot is a destructive viral disease caused by Papaya ringspot virus, commonly transmitted by several aphid species in a non-persistent manner.

Symptoms:

• Mosaic, mottling, and distortion of young leaves
• Narrow, shoestring-like leaf lobes in severe cases
• Oily or water-soaked streaks on petioles and stems
• Circular or ring-shaped marks on fruits
• Stunting, reduced fruit size, poor quality, and severe yield loss

Integrated management:

• Use healthy seedlings and tolerant or resistant cultivars where available.
• Raise the nursery away from infected papaya fields.
• Remove and destroy infected plants promptly to reduce virus sources.
• Eliminate volunteer papaya plants and important alternate weed hosts.
• Establish barrier crops around young plantations where locally recommended.
• Use reflective mulch or other validated practices that interfere with aphid landing.
• Avoid overlapping old infected crops with new plantations.
• Maintain balanced nutrition to support crop vigor.

Insecticides alone cannot reliably prevent transmission because aphids can acquire and transmit the virus rapidly before being killed. Area-wide sanitation and early roguing are therefore essential.

Maturity assessment:

• Fruits attain full size and the surface becomes smoother.
• Latex changes from milky and abundant to more watery.
• The peel begins to change from dark green to light green or yellow.
• For distant markets, fruits are harvested at the color-break stage when a slight yellow streak appears.
• For local markets, fruits may be harvested at a more advanced yellow stage.

Harvesting:

• Harvest fruits individually by hand or with a suitable picking device.
• Retain a short stalk and avoid puncturing the skin.
• Use ladders or padded harvesters for tall plants rather than dropping fruits.
• Place fruits in padded containers to prevent bruising and latex stains.

Post-harvest management:

• Wash fruits carefully and use only approved sanitation or disease-control treatments.
• Grade by size, maturity, shape, and absence of defects.
• Wrap or cushion individual fruits and pack them in ventilated cartons.
• Pre-cool where facilities are available.
• Store at a maturity-appropriate temperature and high relative humidity while avoiding chilling injury.
• Maintain a continuous cool chain during transport and marketing.

Careful handling is essential because ripe papaya has soft pulp and is highly susceptible to compression and impact damage.

Commercial citrus groups:

• Mandarins: Citrus reticulata and related hybrids
• Sweet oranges: Citrus sinensis
• Acid limes: commonly Citrus aurantiifolia and Citrus latifolia
• Lemons: Citrus limon
• Grapefruits: Citrus paradisi
• Pummelos: Citrus maxima

Distinguishing features:

• Mandarins: Usually have loose, easily peeled skin, readily separable segments, rich aroma, and relatively flattened fruits.
• Sweet oranges: Generally possess tighter skin, rounded fruits, firm segments, and sweet juice with balanced acidity.
• Acid limes: Usually produce small, thin-skinned fruits with highly acidic juice and a characteristic aroma.
• Lemons: Fruits are commonly larger and more elongated than limes, often with a nipple at the apex, thicker rind, and strongly acidic juice.

These groups differ in climate adaptation, tree growth, fruit morphology, peel adherence, flavor, juice composition, seediness, and commercial use.

Most commercial citrus cultivars are budded onto rootstocks. The rootstock affects tree survival, vigor, productivity, fruit quality, and adaptation to soil and climatic stresses.

Important selection characteristics:

• Compatibility with the scion cultivar
• Adaptation to soil pH, salinity, calcareousness, and drainage
• Tolerance to drought, cold, or temporary excess moisture
• Resistance or tolerance to soil-borne diseases and nematodes
• Influence on tree size, precocity, yield, fruit size, juice content, and maturity
• Suitability for local disease conditions, including tristeza and Phytophthora risks
• Ability to produce uniform, vigorous, and often nucellar seedlings

Examples:

• Rough lemon has traditionally been valued for vigor and drought adaptation but may produce coarse fruit and has limitations under some disease conditions.
• Trifoliate orange and some of its hybrids can provide cold tolerance and tree-size control but may perform poorly in highly calcareous soils.
• Rangpur lime is vigorous and drought tolerant in many environments but is unsuitable where particular disease pressures make it vulnerable.

No rootstock is universally best. Selection must match the scion, soil, climate, irrigation-water quality, planting density, and locally important diseases.

T-budding procedure:

1. Raise uniform, healthy rootstock seedlings of suitable stem thickness.
2. Select mature, disease-free budwood from a certified mother tree.
3. Make a vertical cut and a short cross-cut on the rootstock bark to form a T shape.
4. Remove a shield-shaped bud piece with a thin sliver of wood from the bud stick.
5. Insert the bud shield beneath the loosened bark flaps of the rootstock.
6. Wrap the union firmly with budding tape while leaving the bud exposed.
7. After union formation, remove the wrapping and cut back or bend the rootstock above the bud.
8. Remove rootstock sprouts and train a single straight scion shoot.

Precautions:

• Use certified, true-to-type, pathogen-tested budwood.
• Select a rootstock compatible with the scion and local conditions.
• Sterilize budding tools between source plants where disease transmission is a concern.
• Perform budding when the bark slips easily and active cambial growth is present.
• Align cambial tissues and prevent the cut surfaces from drying.
• Maintain nursery sanitation and control insect vectors.
• Reject plants with weak unions, off-type growth, root deformities, or disease symptoms.

Orchard establishment:

• Select a well-drained site with suitable soil depth and good-quality irrigation water.
• Test the soil and water before planting.
• Prepare pits and incorporate well-decomposed organic manure.
• Use certified, disease-free budded plants with a sound root system.
• Plant at the same depth as in the nursery and keep the bud union above the soil line.
• Spacing commonly ranges from about to , depending on species, rootstock, and vigor.

Irrigation:

• Irrigate immediately after planting and maintain adequate moisture during establishment.
• Drip irrigation is efficient and reduces wetting of the trunk.
• Avoid water stress during flowering, fruit set, and fruit enlargement.
• Prevent waterlogging and direct contact of irrigation water with the trunk collar.

Nutrition:

• Follow soil and leaf analysis for fertilizer planning.
• Apply nitrogen in split doses and supply phosphorus, potassium, organic matter, and micronutrients as required.

Training and pruning:

• Develop a clean trunk and well-distributed scaffold branches.
• Remove rootstock suckers, dead wood, crossing branches, and diseased shoots.
• Avoid severe routine pruning because citrus generally bears on peripheral growth.

Weed control:

• Combine mulching, shallow cultivation, cover crops, and carefully directed herbicides where approved.
• Keep weeds away from young trunks and avoid damaging shallow feeder roots.

Citrus decline is a gradual reduction in tree vigor and productivity. It is a syndrome rather than a single disease and may result from interacting biotic and abiotic factors.

Common symptoms:

• Sparse foliage and twig dieback
• Leaf yellowing and micronutrient-deficiency patterns
• Reduced shoot growth, flowering, fruit size, and yield
• Premature fruit drop
• Root decay, bark lesions, or poor bud-union condition
• Eventual drying of major limbs or death of the tree

Possible causes:

• Incompatible or unsuitable rootstock
• Tristeza, greening or huanglongbing, and other graft-transmissible pathogens
• Phytophthora foot rot and root rot
• Nematodes and root-feeding pests
• Poor drainage, salinity, drought, or nutrient imbalance
• Improper irrigation, deep planting, and trunk injury

Integrated diagnosis and management:

1. Examine symptom distribution, roots, trunk, bud union, and irrigation pattern.
2. Test soil, water, and leaf nutrient status.
3. Use laboratory diagnosis for suspected pathogens.
4. Plant certified disease-free material on locally suitable rootstocks.
5. Improve drainage, irrigation scheduling, organic matter, and balanced nutrition.
6. Manage insect vectors and soil-borne pathogens using locally recommended integrated practices.
7. Remove severely infected trees when they act as reservoirs of incurable pathogens.

Accurate diagnosis is essential because fertilizer alone cannot correct decline caused by systemic disease or root damage.