📈 Diseases of Cruciferous Vegetables

Cruciferous vegetables (family Brassicaceae) include cabbage, cauliflower, broccoli, radish, turnip, and mustard. These crops are affected by several important diseases caused by fungi, bacteria, and viruses.

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Club Root

Causal Organism: Plasmodiophora brassicae Woronin — an obligate parasite (Plasmodiophoromycota)

Symptoms

• Roots develop large, irregular, spindle-shaped or club-like swellings (galls)
• Above-ground, plants show wilting during the day with recovery at night (in early stages)
• Stunted growth, yellowing, and premature bolting
• Severely affected plants fail to form heads in cabbage and cauliflower

Disease Cycle

Resting spores survive in the soil for 15-20 years. They germinate to produce zoospores that infect root hairs. The pathogen completes its life cycle within root cells, producing secondary zoospores and eventually new resting spores upon root decay.

Management

• Lime the soil to raise pH above 7.2 (the pathogen is suppressed in alkaline conditions)
• Practice long crop rotation (5-7 years) with non-cruciferous crops
• Raise seedlings in sterilised or pasteurised nursery media
• Avoid waterlogged conditions that favour zoospore movement

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Black Rot

Causal Organism: Xanthomonas campestris pv. campestris (Bacterium)

Symptoms

• V-shaped, yellow to brown lesions starting from the leaf margins
• Veins within the lesion turn black, giving a characteristic "black-veined" appearance
• Affected areas become dry and papery
• Systemic infection leads to darkening of the vascular ring in stems and heads

Spread and Favourable Conditions

Factor	Detail
Primary inoculum	Infected seed
Spread	Rain splash, irrigation water, insects
Optimum temperature	25-30 degrees C
Favourable conditions	Warm, humid, rainy weather

Management

• Use hot water-treated seed (50 degrees C for 30 minutes) to eliminate seed-borne inoculum
• Spray Streptocycline (100 ppm) + Copper oxychloride (0.25%)
• Remove and destroy infected plant debris
• Practice crop rotation for 2-3 years with non-cruciferous crops

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Downy Mildew

Causal Organism: Peronospora parasitica (syn. Hyaloperonospora brassicae)

Symptoms

• Yellow, angular patches on the upper leaf surface, limited by veins
• White to greyish-purple downy fungal growth on the corresponding lower surface
• Severely affected seedlings may die; in mature plants, leaves turn brown and dry

Management

• Spray Metalaxyl + Mancozeb (Ridomil MZ, 0.25%) at first appearance of symptoms
• Ensure proper spacing and air circulation in nursery beds
• Avoid overhead irrigation
• Grow resistant varieties such as Pusa Snowball K-1 (cauliflower)

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Alternaria Leaf Spot

Causal Organism: Alternaria brassicae and A. brassicicola

Symptoms

• Dark brown to black, circular spots with concentric rings (target-board pattern) on leaves
• Spots enlarge and coalesce, causing premature defoliation
• Pod infection in mustard causes shrivelled, low-quality seed

Management

• Seed treatment with Mancozeb (2.5 g/kg seed) or Iprodione
• Spray Mancozeb (0.25%) or Iprodione (0.2%) at 15-day intervals
• Remove infected crop debris after harvest
• Use resistant varieties such as Pusa Bold in mustard

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Summary Cheat Sheet

Disease	Causal Organism	Hallmark Symptom	Core Management
Club root	Plasmodiophora brassicae	Club-like root galls and stunting	Liming + long rotation + clean nursery media
Black rot	Xanthomonas campestris pv. campestris	V-shaped marginal lesions with black veins	Hot water seed treatment + copper sprays
Downy mildew	Peronospora parasitica	Yellow angular patches with lower downy growth	Metalaxyl+Mancozeb + better aeration
Alternaria leaf spot	Alternaria spp.	Concentric ringed dark spots	Seed treatment + periodic fungicide spray

References

2 sources • [1] [2]

[1]

Indian Council of Agricultural Research (ICAR)

Official

[2]

CABI Crop Protection Compendium

Website