Nothopassalora leaf spot

Nothopassalora leaf spot is a fungal disease caused by the pathogen Nothopassalora personata. This microscopic fungus is widely known as the causative agent of late leaf spot in groundnuts (peanuts). It belongs to the group of foliar pathogens that significantly affect the physiological development of the host plant.

The disease primarily targets leguminous crops, making it a critical concern for agricultural production in tropical and subtropical regions. The fungus attacks the foliage, petioles, and stems of plants, leading to severe defoliation which interrupts the plant's ability to produce energy through photosynthesis, ultimately impacting yield formation.

Typical symptoms involve the appearance of dark, roughly circular spots on the leaves, frequently surrounded by a yellow chlorotic halo. Under high humidity conditions, the underside of the leaves may become covered with a dark, velvety layer of conidiophores and conidia. As the disease progresses, these spots coalesce, causing leaves to wither and detach prematurely.

Environmental conditions play a decisive role in the spread of the disease. Prolonged periods of warm temperatures combined with high relative humidity and leaf wetness are essential for spore germination and colonization. The pathogen survives in the soil and on infected crop debris, allowing it to re-infect subsequent crops if rotation cycles are not managed properly.

The impact on yield is substantial, often leading to reduced pod development and lower oil content in the seeds. To effectively mitigate the risk, farmers should employ an integrated disease management strategy:

• Implementing crop rotation with non-host plants for at least two years.
• Removing and burying infected crop residues to reduce the initial inoculum level.
• Utilizing disease-resistant cultivars available in the regional market.
• Applying preventive or curative fungicides according to local agronomic guidelines and weather forecasts.