A) Panama Disease of Banana

Pathogen: Fusarium oxysporum f. sp. cubense

Economic Importance:

• Panama disease is a devastating soil-borne fungal disease affecting banana crops worldwide.
• Named after Panama, where it first caused severe damage.
• It severely impacts banana production, especially in poorly drained soils.
• The disease is transmitted through infected suckers and contaminated soil, leading to significant yield losses.

Symptoms:

• Yellowing of the lower leaves, starting from the leaf margins and moving towards the midrib.
• Progressive yellowing extends upwards, leaving the heart leaf green for a while before it also becomes affected.
• Leaves break near the base and hang down around the pseudostem, giving a skirt-like appearance.
• Longitudinal splitting of the pseudostem is common.
• Discoloration of vascular tissues is observed as red or brown streaks when the pseudostem is cut open.
• Infected plants eventually wilt and die.

Pathogen Characteristics:

• Mycelium is septate, hyaline, and branched.
• Microconidia: Single-celled or occasionally one-septate, hyaline, elliptical or oval.
• Macroconidia: Sickle-shaped, hyaline, 3-5 septate, tapering at both ends.
• Chlamydospores: Thick-walled, spherical to oval, hyaline to slightly yellowish, enabling long-term survival in soil.

Mode of Spread and Survival:

• The pathogen is soil-borne and can survive in the soil for long periods as chlamydospores.
• Primary spread: Through the use of infected rhizomes (suckers).
• Secondary spread: Through irrigation water, farm tools, and machinery contaminated with the fungus.
• Continuous cultivation of susceptible varieties leads to a build-up of the inoculum in the soil.

Favorable Conditions:

• Poorly drained soils and high soil moisture favor the development and spread of the disease.
• Warm temperatures (25-30°C) enhance fungal growth and infection.

Management Strategies:

i) Cultural Practices:

1. • Avoid growing susceptible cultivars such as Rasthali, Monthan, Red Banana, and Virupakshi.
   • Grow resistant cultivars like Poovan.
   • Practice crop rotation with non-host plants to reduce soil inoculum.
   • Use disease-free planting material from certified nurseries.

ii) Soil and Water Management:

1. • Ensure good soil drainage to reduce waterlogging and prevent fungal spread.
   • Avoid using contaminated irrigation water.

iii) Chemical Control:

1. • Corm injection of 3 ml of 2% Carbendazim by making a hole to a depth of 10 cm at a 45° angle, applied in the 5th and 7th month after planting.
   • Application of Carbofuran granules helps control nematodes that predispose plants to the disease.

iv) Nematode Management:

1. • Since nematodes facilitate fungal entry through root wounds, effective nematode management is essential.
   • Use of nematicides like Carbofuran or biological control agents like Paecilomyces lilacinus.

v) Sanitation and Hygiene:

1. • Remove and destroy infected plants to prevent disease spread.
   • Disinfect tools and machinery before using them in uninfected fields.

vi) Integrated Disease Management (IDM): Combine cultural practices, resistant varieties, soil management, chemical control, and sanitation measures for effective disease control.

Preventive Measures:

• Avoid continuous cultivation of bananas in the same field.
• Monitor fields regularly for early detection and management.
• Quarantine measures to prevent the spread to new areas.

B) Sigatoka Disease of Banana

Pathogen: Mycosphaerella musicola (Anamorph: Cercospora musae)

Economic Importance:

• Sigatoka disease is one of the most serious leaf diseases of bananas worldwide.
• It significantly reduces photosynthetic activity by causing premature leaf death.
• Leads to reduced fruit size and quality, impacting overall yield.

Symptoms:

• Small light yellow or brownish-green narrow streaks initially appear on the leaves.
• These streaks enlarge and become linear, oblong, brown to black spots with a dark brown border and a yellow halo.
• Black specks of fungal fruiting bodies (conidia) develop on the affected areas.
• Rapid drying and defoliation of leaves occur as the disease progresses.
• Severely affected plants may produce smaller bunches with poor fruit quality.

Pathogen Characteristics:

• Conidia: Elongated, narrow, and multi-septate, measuring 20–80 x 2–6 µm.
• Perithecia: Dark brown to black structures containing asci that are oblong to clavate, measuring 28.8–36.8 x 8.0–10.8 µm.
• Ascospores: One-septate, hyaline, obtuse with the upper cell slightly broader than the lower cell.

Disease Cycle:

• The pathogen overwinters on infected leaves and debris.
• Primary infection occurs through conidia or ascospores, which are spread by wind and rain splashes.
• Secondary infection continues as conidia are dispersed from existing lesions to new leaf tissues.
• High humidity (above 90%) and temperatures of 25–28°C favor spore germination and infection.
• Frequent rainfall and poor air circulation enhance disease severity.

Mode of Spread and Survival:

• The disease spreads through wind-borne conidia and rain-splashed spores.
• It survives on infected leaf debris and continues to produce spores under favorable conditions.
• Continuous cultivation of susceptible varieties leads to a build-up of inoculum.

Management Strategies:

i) Cultural Practices:

• • Removal and destruction of affected leaves to reduce inoculum load.
  • Improve air circulation by maintaining optimal plant spacing and pruning excess leaves.
  • Use disease-free planting material from certified sources.
  • Crop rotation with non-host crops to break the disease cycle.

ii) Chemical Control:

• • Spray Propiconazole + Carbendazim (0.1%) or Chlorothalonil (0.25%) to control the fungus.
  • Add a wetting agent like Teepol or Sandovit at the rate of 1 ml/liter of water for better coverage and penetration.
  • Rotate fungicides with different modes of action to avoid resistance buildup.

iii) Resistant Varieties: Planting resistant cultivars where available can provide effective control.

iv) Integrated Disease Management (IDM): Combine cultural practices, resistant varieties, chemical control, and sanitation measures for effective disease management. Regular monitoring for early detection and timely application of fungicides.

Preventive Measures:

• Avoid overhead irrigation to minimize leaf wetness and disease spread.
• Maintain field sanitation by removing fallen leaves and debris.
• Quarantine measures to prevent the spread to disease-free areas.

C) Bunchy Top Disease of Banana

Pathogen: Banana Bunchy Top Virus (BBTV)
Vector: Banana Aphid (Pentalonia nigronervosa)

Economic Importance:

• Bunchy top disease is one of the most destructive viral diseases of bananas worldwide.
• It causes stunted growth and failure to produce fruit, leading to significant yield losses.
• Once infected, the plant remains stunted and unproductive, making the disease economically devastating for banana farmers.

Symptoms:

i) Leaf Symptoms:

• • Dark green streaks on leaf veins, petioles, and midribs, which are the characteristic symptoms of BBTV.
  • Shortened leaf blades and narrow, erect leaves giving a “bunched” appearance at the top of the plant, hence the name “bunchy top.”
  • Chlorotic (yellow) margins along the leaf veins.
  • Leaves become brittle and stand upright, forming a rosette or “bunchy” appearance.

ii) Growth Symptoms:

• • Stunted growth and failure to produce new leaves.
  • Reduction in leaf size with progressive infection.
  • No fruit production or the production of small, deformed fruits.
  • Infected plants remain small, stunted, and unproductive throughout their life cycle.

Pathogen Characteristics:

• Banana Bunchy Top Virus (BBTV) is a circular, single-stranded DNA virus belonging to the Nanoviridae family.
• It is transmitted by the banana aphid (Pentalonia nigronervosa) in a persistent circulative manner, meaning the aphid retains the virus for life once acquired.

Disease Cycle:

i) Primary Spread: Occurs through the use of infected suckers (planting material). Infected suckers produce stunted and symptomatic plants.

ii) Secondary Spread: Transmitted by the banana aphid (Pentalonia nigronervosa) from infected to healthy plants. The aphid acquires the virus by feeding on infected plants and can transmit it throughout its life.

Mode of Spread and Survival:

• The disease spreads through:
  • Infected planting material (suckers and rhizomes).
  • Aphid vectors that feed on infected plants and then move to healthy plants.
• The virus persists in infected plants and can spread through vegetative propagation.
• No seed transmission occurs, but the virus remains in infected suckers used for propagation.

Management Strategies:

i) Cultural Practices:

• • Use virus-free planting material from certified sources.
  • Remove and destroy infected plants to reduce inoculum sources.
  • Control aphid populations by removing alternative host plants around banana plantations.
  • Plant barrier crops like maize or sorghum to limit aphid movement.

ii) Chemical Control:

• • Apply insecticides to control aphid vectors, especially during early plant growth stages.
  • Systemic insecticides such as imidacloprid can be used for effective aphid management.
  • Rotate insecticides to avoid resistance buildup in aphid populations.

iii) Resistant Varieties:

• • Cultivate resistant or tolerant cultivars if available in the region.
  • Research is ongoing for the development of BBTV-resistant banana varieties.

iv) Integrated Disease Management (IDM):

• • Combine cultural practices, chemical control, resistant varieties, and field sanitation.
  • Regular monitoring and scouting for early detection of symptoms and aphid infestations.

Preventive Measures:

• Quarantine and certification programs to ensure virus-free planting material.
• Education and awareness programs for farmers on the importance of using healthy suckers.
• Eradication programs in newly affected areas to prevent disease spread.
• Strict quarantine regulations to prevent the movement of infected planting material.

D) Bacterial Wilt of Banana

Pathogen: Xanthomonas campestris pv. musacearum
Common Name: Banana Xanthomonas Wilt (BXW)

Economic Importance:

• Bacterial wilt is one of the most destructive diseases of bananas and plantains in East and Central Africa.
• It leads to significant yield losses and can wipe out entire banana plantations if not managed.
• The disease affects all parts of the banana plant, including leaves, fruits, and corms, leading to plant death.

Symptoms:

i) Leaf Symptoms:

• • Yellowing and wilting of leaves, starting from the leaf margins and moving inwards.
  • Premature wilting and drying of leaves, leading to a scorched appearance.
  • V-shaped yellowing at the leaf tips, progressing towards the petiole.

ii) Fruit Symptoms:

• • Premature ripening of fruits in an uneven manner.
  • Internal discoloration of the fruit pulp, showing brownish streaks.
  • Rotting and oozing of yellowish bacterial slime from cut surfaces of fruits.

iii) Pseudostem and Vascular Symptoms:

• • Yellow bacterial ooze exudes from cut surfaces of the pseudostem.
  • Internal discoloration of vascular bundles, showing yellow to brown streaks.
  • Wilting and eventual death of the whole plant.

iv) Other Symptoms:

• • Stunting of young plants and poor bunch formation.
  • Uneven and distorted fruit development.

Pathogen Characteristics:

• Xanthomonas campestris pv. musacearum is a Gram-negative bacterium.
• It produces yellow bacterial ooze that is visible when infected plant parts are cut.
• The bacteria enter the plant through wounds, insect feeding sites, and natural openings.

Disease Cycle:

1. Primary Spread:
   • Infected planting material (suckers and corms) are the primary source of inoculum.
   • Contaminated tools used during pruning or harvesting can transmit the bacteria.
2. Secondary Spread:
   • Insect vectors like bees and fruit flies that feed on infected male buds and flowers.
   • Rain splash and irrigation water spread the bacteria from infected plants to healthy ones.
   • Human activities, such as movement of infected plant parts and contaminated tools.

Mode of Spread and Survival:

• The pathogen spreads through:
  • Infected planting material (suckers and rhizomes).
  • Insect vectors like bees and fruit flies.
  • Contaminated pruning tools and farm equipment.
  • Rain splash, irrigation water, and soil movement.
• It survives in crop residues and can persist in the soil for several months.

Management Strategies:

i) Cultural Practices:

• • Use clean planting material from certified sources.
  • Remove and destroy infected plants to reduce the spread of the disease.
  • Sterilize pruning tools using disinfectants like sodium hypochlorite or ethanol.
  • Avoid irrigation practices that facilitate water movement from infected to healthy plants.
  • Rogueing: Uproot and bury affected plants to prevent further spread.

ii) Sanitation and Hygiene:

• • Disinfect tools before moving from one plant to another.
  • Control insect vectors to minimize transmission.
  • Remove male buds soon after fruit set to reduce insect-mediated spread.

iii) Resistant Varieties:

• • Cultivate resistant or tolerant cultivars if available in the region.
  • Research is ongoing for the development of BXW-resistant banana varieties.

iv) Integrated Disease Management (IDM):

• • Combine cultural practices, sanitation, resistant varieties, and vector control.
  • Regular monitoring and scouting for early detection of symptoms.
  • Awareness and training programs for farmers to recognize and manage BXW.

Preventive Measures:

• Quarantine regulations to prevent the movement of infected planting material.
• Community awareness programs to educate farmers on disease identification and management.
• Early detection and rapid response to newly infected fields.
• Training farmers on the importance of tool sterilization and hygiene practices.