🍬 Sugarcane & Tobacco Diseases — Pathogens, Symptoms, and Management

From Field to Lab — Protecting India's Sugar Bowl

India is the world's second-largest sugarcane producer, with UP, Maharashtra, and Karnataka leading production. When a farmer splits open a sugarcane stalk and finds reddened internal tissues with white cross-wise patches and a sour smell, the diagnosis is clear — Red Rot, the "cancer of sugarcane." A central shoot that converts into a long, dusty black whip signals Smut. Setts that smell like pineapple and decay before germination indicate Sett Rot. These diseases collectively cause losses worth thousands of crores annually.

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Sugarcane Diseases

Sugarcane is affected by several fungal, bacterial, and phytoplasmal diseases. Understanding the key pathogens and their diagnostic symptoms is critical for competitive exams.

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1. Red Rot — Colletotrichum falcatum

Symptoms:

• First external symptom appears on the 3rd or 4th leaf — withering at tips along margins
• Splitting the stalk longitudinally reveals reddening of internal tissues elongated at right angles to the long axis
• Cross-wise white patches within the red areas are the most important diagnostic character
• Diseased cane emits an acidic-sour smell
• As disease advances, stalk becomes hollow and covered with white mycelial growth

Favourable Conditions:

• Monoculturing of sugarcane
• Successive ratoon cropping
• Waterlogged conditions and insect injuries

Management:

• Soak setts in 0.25% Agallol or Aretan solution for 5 minutes
• Treat setts with aerated steam at 52°C for 4-5 hours or moist hot air at 54°C for 2 hours
• Use resistant varieties and avoid ratooning of infected fields

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2. Smut — Ustilago scitaminea

Symptoms:

• It is a culmiculous smut affecting the stalk of cane
• Severe from April to July; causes ~10% loss in juice
• Affected plants are stunted; central shoot converts into a long whip-like, dusty black structure

Management:

• Discourage ratooning of diseased crops having more than 10% infection
• Grow redgram as a companion crop between 2 rows of sugarcane
• Use resistant varieties

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3. Sett Rot / Pineapple Disease — Ceratocystis paradoxa

Symptoms:

• Fungus is soil-borne; enters through cut ends and proliferates in parenchymatous tissues
• Affected tissues first develop a reddish colour turning to brownish black later
• Severely affected setts show internodal cavities covered with mycelium and abundant spores
• Setts may decay before bud germination or shoots may die after reaching 6-12 inches
• Infected shoots are stunted

Management:

• Treat setts with fungicides before planting
• Use healthy, disease-free planting material
• Avoid planting in waterlogged soils

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4. Wilt — Cephalosporium sacchari

Symptoms:

• Gradual yellowing and drying of leaves
• Internal tissues of the stalk show discolouration
• Plants wilt and eventually die

Management:

• Use resistant varieties
• Remove and destroy infected plants
• Practice crop rotation

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5. Red Stripe — Pseudomonas rubrilineans

Symptoms:

• Disease first appears on the basal part of young leaves
• Stripes appear as water-soaked, long, narrow chlorotic streaks that become reddish brown in a few days, running parallel to the midrib
• Rotting may commence from the tip of the shoot and spread downwards
• In badly affected fields, a foul and nauseating smell appears

Management:

• Use disease-free planting material
• Rogue out infected plants
• Grow resistant varieties

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6. Grassy Shoot Disease — Phytoplasma

Symptoms:

• Disease appears nearly two months after planting
• Characterised by production of numerous lanky tillers from the base of affected shoots
• Leaves become pale yellow to completely chlorotic, thin and narrow
• Plants appear bushy and "grass-like" due to reduction in internode length, premature and continuous tillering
• Buds on infected canes are usually papery and abnormally elongated

Management:

• Use disease-free seed material
• Hot water treatment of setts at 50°C for 2 hours
• Rogue out diseased clumps

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7. Ratoon Stunting Disease — Clavibacter xyli sub sp. xyli

Symptoms:

• Diseased clumps display stunted growth, reduced tillering, thin stalks with shortened internodes
• Yellowish foliage
• Pink vascular bundles in shades of yellow at the nodes are seen in infected canes

Management:

• Hot water treatment of setts at 50°C for 2 hours
• Use disease-free planting material
• Avoid ratooning of infected crops

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Minor Diseases of Sugarcane

Other Sugarcane Diseases — Quick Reference

Disease	Pathogen
Damping-off	Pythium aphanidermatum, P. debaryanum, P. graminicola, P. ultimum
Downy mildew	Peronosclerospora sacchari
Rust	Puccinia erianthi
Gummosis	Xanthomonas axonopodis pv. Vasculorum (fibro-vascular becomes red)
Sugarcane Mosaic	Sugarcane mosaic potyvirus

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Tobacco Diseases

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1. Damping Off — Pythium aphanidermatum

Symptoms:

• Pre-emergence damping off: Seeds rot before emergence
• Post-emergence damping off: Water-soaked minute lesions appear on stems near soil surface, girdling the stem; within 1-2 days stem may rot, causing toppling of seedlings
• Young seedlings in the nursery are killed in patches; infection spreads quickly
• Under favourable conditions, entire seedlings in the nursery are killed within 3-4 days

Management:

• Seed treatment with Thiram or Captan @ 2-3 g/kg
• Drench nursery beds with Copper oxychloride (0.25%)
• Ensure proper drainage in nursery

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2. Tobacco Mosaic — Tobacco mosaic virus (TMV)

Symptoms:

• In severe infections, leaves are narrowed, puckered, thin, and malformed beyond recognition
• Under hot weather, dark brown necrotic spots develop — called "Mosaic burn" or "Mosaic scorching"

Management:

• Remove and destroy infected plants
• Wash hands with soap/milk before handling healthy plants
• Use resistant varieties
• Control of insect vectors

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3. Leaf Curl — Tobacco leaf curl virus (TLCV)

Symptoms:

• Infections may occur at any stage; young infected plants remain very much dwarfed
• Curling of leaves with clearing and thickening of veins; twisting of petioles
• Puckering of leaves; rugose and brittle texture
• Development of enations is an important symptom

Management:

• Control whitefly vector (Bemisia tabaci)
• Remove infected plants early
• Use resistant varieties

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Minor Diseases of Tobacco

Other Tobacco Diseases — Quick Reference

Disease	Pathogen
Powdery mildew	Erysiphe cichoracearum var. nicotianae
Anthracnose	Colletotrichum tabacum
Black shank	Phytophthora parasitica var. nicotianae
Frog eye spot	Cercospora nicotianae

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Summary Cheat Sheet

Fact	Answer
Most destructive disease of sugarcane	Red Rot (Colletotrichum falcatum)
"Cancer of sugarcane"	Red Rot
Diagnostic character of Red Rot	Cross-wise white patches within red internal tissue + acidic-sour smell
Sugarcane Smut pathogen	Ustilago scitaminea — "Whip Smut"
Smut symptom	Long whip-like dusty black structure from central shoot
Sett Rot / Pineapple Disease pathogen	Ceratocystis paradoxa
Sett Rot key symptom	Pineapple smell + internodal cavities
Sugarcane Wilt pathogen	Cephalosporium sacchari
Red Stripe pathogen	Pseudomonas rubrilineans
Grassy Shoot Disease cause	Phytoplasma — numerous lanky tillers, grass-like bushy plants
Ratoon Stunting Disease pathogen	Clavibacter xyli subsp. xyli (RLO — Rickettsia-Like Organism)
Ratoon Stunting key symptom	Pink vascular bundles at nodes
Sugarcane Sett treatment	0.25% Agallol/Aretan for 5 min OR steam at 52°C for 4–5 hrs
Tobacco Damping Off pathogen	Pythium aphanidermatum
First virus discovered	Tobacco Mosaic Virus (TMV) — Ivanowsky (1892), crystallized by Stanley (1935)
TMV symptom in hot weather	Mosaic burn / Mosaic scorching — dark brown necrotic spots
Tobacco Leaf Curl vector	Whitefly (Bemisia tabaci)
Leaf Curl key symptom	Vein clearing + thickening, curling of leaves, enations
Sugarcane Rust pathogen	Puccinia erianthi
Sugarcane Downy Mildew pathogen	Peronosclerospora sacchari

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Quick Revision Table

Crop	Disease	Pathogen	Key Diagnostic Feature
Sugarcane	Red Rot	Colletotrichum falcatum	Red patches with white centre, acidic-sour smell
Sugarcane	Smut	Ustilago scitaminea	Whip-like black structure from central shoot
Sugarcane	Sett Rot	Ceratocystis paradoxa	Pineapple smell, internodal cavities
Sugarcane	Wilt	Cephalosporium sacchari	Yellowing, internal discolouration
Sugarcane	Red Stripe	Pseudomonas rubrilineans	Water-soaked streaks parallel to midrib
Sugarcane	Grassy Shoot	Phytoplasma	Grass-like bushy appearance, lanky tillers
Sugarcane	Ratoon Stunting	Clavibacter xyli subsp. xyli (RLO)	Pink vascular bundles at nodes
Tobacco	Damping Off	Pythium aphanidermatum	Water-soaked lesions, seedling collapse
Tobacco	TMV	Tobacco mosaic virus	Mosaic burn/scorching, first virus discovered
Tobacco	Leaf Curl	TLCV	Vein clearing, leaf curling, enations