Philippine downy mildew of maize

The causative agent of the disease is the oomycete Peronosclerospora maydis, which belongs to the downy mildew pathogen group. It is a highly destructive, systemic pathogen that infects maize seedlings at an early stage, leading to stunted growth, severe physiological disorders, and often complete plant mortality before maturity.

Maize is the primary host for this pathogen. The fungus invades the seedlings through the mesocotyl tissue. Once the internal infection is established, the mycelium colonizes the apical meristem, disrupting the development of leaf primordia and causing systemic infection that persists throughout the plant's life cycle.

Key symptoms include chlorotic streaks on the leaves, which eventually turn pale yellow. Under conditions of high humidity, a dense white fungal growth, consisting of conidiophores and conidia, develops on the abaxial side of the leaf blades. Affected plants often exhibit stunted growth, excessive tillering, and failure to produce healthy ears.

The development and spread of Peronosclerospora maydis are heavily dependent on warm temperatures and high relative humidity. The pathogen produces airborne conidia that travel easily under favorable weather conditions. The presence of free moisture, such as dew or light rain, is essential for the germination of spores and subsequent infection of the plant tissues.

The economic impact of this disease is severe, with potential yield losses reaching up to 100% in susceptible fields. Integrated pest management strategies include the use of resistant maize hybrids, high-quality fungicide seed treatments, and cultural practices such as crop rotation and the destruction of infected plant debris to minimize the primary inoculum in the soil and surrounding environment.