LEAF SPOT OF CAULIFLOWER
Comprehensive Study & Reference Notes
Plant Pathology | Vegetable Diseases | Brassica Diseases
EXAM TIP: Leaf spot is caused by multiple pathogens. Always check whether the question
refers to Alternaria, Cercospora, or Xanthomonas — each has distinct features that are
frequently tested!
1. INTRODUCTION
Leaf spot of cauliflower is a significant foliar disease complex affecting Brassica oleracea var. botrytis
worldwide. It leads to considerable economic losses by reducing photosynthetic area, weakening the
plant, and in severe cases, destroying the marketable curds. Understanding the causal organisms,
biology, symptoms, and management is critical for students of plant pathology and agronomy.
2. CAUSAL ORGANISMS
Leaf spot of cauliflower is a disease complex involving both fungal and bacterial agents:
2.1 Alternaria Leaf Spot (Most Common)
• Pathogen: Alternaria brassicae and Alternaria brassicicola
• Kingdom: Fungi | Class: Deuteromycetes (Hyphomycetes)
• Type: Imperfect fungi — reproduce asexually by conidia
• Note: A. brassicae is more prevalent in warm, humid climates; A. brassicicola in cooler regions
2.2 Cercospora Leaf Spot
• Pathogen: Cercospora brassicicola
• Kingdom: Fungi | Class: Deuteromycetes
• Distribution: Less common; occurs in tropical and subtropical regions
• Lesions: Pale/white center with dark borders — characteristic feature
2.3 Bacterial Leaf Spot
, • Pathogen: Xanthomonas campestris pv. campestris
• Kingdom: Bacteria | Family: Xanthomonadaceae
• Lesions: Angular, water-soaked, limited by leaf veins
2.4 Comparison of Causal Organisms
Feature Alternaria brassicae Cercospora brassicicola Xanthomonas campestris
Type Fungus Fungus Bacterium
Lesion Shape Circular/oval Circular Angular (vein-limited)
Lesion Color Dark brown/black Pale, dark margin Water-soaked, yellow halo
Concentric Rings Yes (target-like) Absent Absent
Sporulation Dark conidia on surface Cercosporae visible Bacterial ooze
Climate Warm & humid Tropical/subtropical Warm & moist
3. SYMPTOMS
3.1 Alternaria Leaf Spot — Symptoms
• Early Stage: Small, circular, dark brown to black spots on leaves
• Advanced Stage: Spots enlarge with characteristic concentric ring pattern (target-board
appearance)
• Spot Size: 3–12 mm diameter; may coalesce to form large necrotic patches
• Yellow Halo: Chlorotic (yellow) halo surrounds the necrotic lesion
• Sporulation: Gray to olive-green powdery conidia on lesion surface (humid conditions)
• Stem & Petiole: Elongated, dark, slightly sunken lesions
• Curd Infection: Dark sunken spots on the curd — reduces market value significantly
• Severe Infection: Premature defoliation, stunted growth, reduced yield
3.2 Cercospora Leaf Spot — Symptoms
• Small circular spots, initially dark, turning pale/white at center
• Dark purple to brown margin surrounding the pale center
• Spots 2–6 mm in diameter; no concentric rings
• Grayish mycelium visible on underside of leaves
3.3 Bacterial Leaf Spot — Symptoms
Comprehensive Study & Reference Notes
Plant Pathology | Vegetable Diseases | Brassica Diseases
EXAM TIP: Leaf spot is caused by multiple pathogens. Always check whether the question
refers to Alternaria, Cercospora, or Xanthomonas — each has distinct features that are
frequently tested!
1. INTRODUCTION
Leaf spot of cauliflower is a significant foliar disease complex affecting Brassica oleracea var. botrytis
worldwide. It leads to considerable economic losses by reducing photosynthetic area, weakening the
plant, and in severe cases, destroying the marketable curds. Understanding the causal organisms,
biology, symptoms, and management is critical for students of plant pathology and agronomy.
2. CAUSAL ORGANISMS
Leaf spot of cauliflower is a disease complex involving both fungal and bacterial agents:
2.1 Alternaria Leaf Spot (Most Common)
• Pathogen: Alternaria brassicae and Alternaria brassicicola
• Kingdom: Fungi | Class: Deuteromycetes (Hyphomycetes)
• Type: Imperfect fungi — reproduce asexually by conidia
• Note: A. brassicae is more prevalent in warm, humid climates; A. brassicicola in cooler regions
2.2 Cercospora Leaf Spot
• Pathogen: Cercospora brassicicola
• Kingdom: Fungi | Class: Deuteromycetes
• Distribution: Less common; occurs in tropical and subtropical regions
• Lesions: Pale/white center with dark borders — characteristic feature
2.3 Bacterial Leaf Spot
, • Pathogen: Xanthomonas campestris pv. campestris
• Kingdom: Bacteria | Family: Xanthomonadaceae
• Lesions: Angular, water-soaked, limited by leaf veins
2.4 Comparison of Causal Organisms
Feature Alternaria brassicae Cercospora brassicicola Xanthomonas campestris
Type Fungus Fungus Bacterium
Lesion Shape Circular/oval Circular Angular (vein-limited)
Lesion Color Dark brown/black Pale, dark margin Water-soaked, yellow halo
Concentric Rings Yes (target-like) Absent Absent
Sporulation Dark conidia on surface Cercosporae visible Bacterial ooze
Climate Warm & humid Tropical/subtropical Warm & moist
3. SYMPTOMS
3.1 Alternaria Leaf Spot — Symptoms
• Early Stage: Small, circular, dark brown to black spots on leaves
• Advanced Stage: Spots enlarge with characteristic concentric ring pattern (target-board
appearance)
• Spot Size: 3–12 mm diameter; may coalesce to form large necrotic patches
• Yellow Halo: Chlorotic (yellow) halo surrounds the necrotic lesion
• Sporulation: Gray to olive-green powdery conidia on lesion surface (humid conditions)
• Stem & Petiole: Elongated, dark, slightly sunken lesions
• Curd Infection: Dark sunken spots on the curd — reduces market value significantly
• Severe Infection: Premature defoliation, stunted growth, reduced yield
3.2 Cercospora Leaf Spot — Symptoms
• Small circular spots, initially dark, turning pale/white at center
• Dark purple to brown margin surrounding the pale center
• Spots 2–6 mm in diameter; no concentric rings
• Grayish mycelium visible on underside of leaves
3.3 Bacterial Leaf Spot — Symptoms
