Seedling Fungal Diseases in Plumeria: Identification, Prevention, and Treatment

Fungal diseases are among the most significant threats to plumeria seedlings, often leading to severe losses during propagation. These pathogens attack roots, stems, and sometimes foliage, causing damping-off, root rot, and vascular wilts. Early identification combined with preventive cultural practices and appropriate treatments can dramatically improve seedling survival and vigor.

Common Fungal Pathogens Affecting Plumeria Seedlings

• Pythium spp.: Known as water molds, these pathogens cause rapid seed rot and damping-off in overly wet conditions. They attack root tips and stem bases, causing soft rot.
• Phytophthora spp.: Similar to Pythium, this genus causes severe root and stem rots, often leading to plant collapse.
• Fusarium spp.: Soilborne fungi that invade vascular tissues, causing wilting and necrosis. They are persistent and often cause chronic problems.
• **Rhizoctonia solani: **Causes root and stem rot, recognizable by reddish-brown lesions and crusty mycelium on roots.

Symptoms and Disease Progression

• Seed Symptoms: Seeds may become soft, waterlogged, or covered with white or gray fungal growth; failure to germinate is common.
• Seedling Symptoms: Young seedlings may emerge but show stunted growth, yellowing, and wilting. Stem bases become water-soaked and brown or black. Seedlings can suddenly collapse at the soil line (pre- or post-emergence damping-off).
• Root Symptoms: Roots may appear blackened, mushy, or with abnormal branching.
• Secondary Symptoms: Leaves may yellow or drop prematurely; seedlings may fail to develop normally.

Environmental Factors Favoring Fungal Diseases

• Excess Moisture: Overwatering or poor drainage leads to saturated soils conducive to fungal growth.
• High Humidity: Prolonged leaf wetness and humid conditions favor fungal sporulation and infection.
• Overcrowding: Dense seedlings create microclimates with high humidity and reduced airflow.
• Contaminated Media or Tools: Fungi can be introduced via dirty seed-starting media, pots, or gardening tools.

Prevention Strategies

• Use sterile seed-starting media free from pathogens.
• Sow seeds in containers or trays that allow excellent drainage.
• Water seedlings moderately; avoid waterlogging and prolonged wetness.
• Space seedlings adequately to improve airflow.
• Surface sterilize seeds prior to sowing to reduce seedborne fungal inoculum.
• Sanitize all propagation equipment regularly.

Treatment Options

• Remove and destroy infected seedlings immediately to prevent spread.
• Apply appropriate fungicides labeled for seedling diseases, such as products containing metalaxyl or thiophanate-methyl.
• Use biological fungicides where available for organic-compatible control.
• Adjust cultural practices to reduce conditions favorable to fungi.