Anthracnose / Black spot

Marssonina spp. e Colletotrichum spp.

1. Identification

Marssonina spp. and Colletotrichum spp. are groups of pathogenic fungi responsible for foliar, stem and fruit diseases in various agricultural crops. The most common diseases include:

Diseases caused by Marssonina spp.:

• Apple leaf spot — caused by Marssonina coronaria Ellis & J.J. Davis
• Walnut leaf spot — caused by Marssonina juglandis Lib.
• Rose leaf spot — caused by Marssonina rosae Lib.

Diseases caused by Colletotrichum spp.:

• Strawberry anthracnose — caused by Colletotrichum acutatum J.H. Simmonds
• Bean anthracnose — caused by Colletotrichum lindemuthianum Sacc. & Magnus
• Citrus anthracnose — mainly caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.
• Mango anthracnose — caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.
• Black rot in solanaceous crops — caused by Colletotrichum coccodes (Wallr.) S.J. Hughes

These species affect horticultural crops, fruit trees, ornamentals and industrial crops, causing significant economic losses.

2. Causal agent

Marssonina spp. belongs to the family Dermateaceae (Ascomycota), producing hyaline conidia released from acervuli formed in infected tissues. Colletotrichum spp. belongs to the family Glomerellaceae (Ascomycota), characterised by hyaline, unicellular, generally fusiform conidia produced in acervuli with characteristic setae. Both survive in crop residues, fallen leaves, seeds and contaminated soils.

3. Main hosts

Marssonina spp.:

• Fruit trees: apple, pear, walnut
• Ornamentals: roses
• Forest species: chestnut, black walnut

Colletotrichum spp.:

• Vegetables: tomato, pepper, cucumber, bean
• Fruit crops: strawberry, citrus, avocado, mango
• Various ornamentals
• Industrial crops: coffee, cotton

4. Symptoms

Symptoms caused by Marssonina spp. begin as small green‑grey circular spots that develop into dark necrotic lesions with a yellow halo. In apple and walnut, the disease causes premature defoliation and reduced photosynthetic capacity. In roses, irregular spots appear, reducing plant vigour.

Colletotrichum spp. causes anthracnose characterised by dark, sunken lesions with defined margins. In fruits, pink to salmon conidial masses may appear. In leaves, lesions may coalesce, leading to necrosis. In stems and petioles, infection may cause cankers and tissue collapse.

Both pathogens progress rapidly under favourable conditions, affecting yield and commercial quality.

5. Disease cycle

Marssonina spp. and Colletotrichum spp. survive in crop residues, fallen leaves, seeds and contaminated soils.

Dispersal:

• Conidia transported by rain
• Conidia transported by irrigation
• Conidia transported by wind
• Conidia spread by plant contact or tools

Infection:

• Favoured by high humidity
• Occurs in young tissues, active leaves, immature fruits and wounds

Polycyclic cycle:

• Multiple infections throughout the season, especially in humid periods

6. Favourable conditions

Humid environments, frequent rainfall, moderate to high temperatures and prolonged leaf wetness favour disease development. High planting density and poor ventilation increase severity. Contaminated crop residues act as a continuous inoculum source.

7. Disease management

Management focuses on reducing leaf wetness, improving ventilation and removing infected tissues. Crop rotation and the use of less susceptible varieties reduce disease pressure. Regular monitoring enables timely interventions. Biological control may be applied with authorised antagonists. Chemical control must follow local regulations and alternate modes of action to prevent resistance.

References

• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• EPPO – Diagnostic Protocols for Marssonina spp.
• EPPO – Diagnostic Protocols for Colletotrichum spp.
• FAO – Guidelines for Integrated Disease Management in Fruit and Horticultural Crops.
• Sutton, B.C. (1992). The Genus Colletotrichum.