Phoma leaf spot of lotus

The disease is caused by the fungus Phoma loti, a significant pathogen primarily targeting species within the Lotus genus. As a member of the Phoma genus, it disrupts plant health through the production of enzymes that degrade host cell walls, leading to localized tissue necrosis. It is a persistent concern in both pasture management and seed production.

The host range is largely confined to Lotus species, with Lotus corniculatus (birdsfoot trefoil) being the most commonly affected crop. The pathogen can attack plants at various growth stages, potentially leading to significant economic losses in forage yield and quality, as well as reducing the longevity of perennial legume stands.

Symptoms appear as small, dark brown spots on leaves, stems, and petioles. These lesions often exhibit a distinct margin and may contain pycnidia—minute, black, flask-shaped structures that house fungal spores. Under favorable conditions, these spots expand rapidly, causing chlorosis, leaf death, and eventual necrosis of infected stems.

Environmental conditions play a critical role in the development of Phoma loti. High relative humidity, moderate temperatures, and prolonged leaf wetness are essential for spore germination and infection. The pathogen spreads via splashing rain and wind-dispersed conidia, with the ability to overwinter on infected plant debris or within contaminated seed lots.

Effective management strategies focus on preventing the buildup of inoculum. Key practices include:

• utilizing disease-free, certified seeds;
• implementing proper crop rotation cycles;
• removing and destroying crop residues through deep tillage;
• maintaining optimal plant density to improve air circulation;
• monitoring fields during wet periods for early signs of infection.