Cercospora kikuchii

Cercospora kikuchii It is a phytopathogenic fungus popularly known as the causal agent of "leaf blight", "purple spot" or "purple leaf spot".

Taxonomic classification:

• Kingdom: Fungi

• Division: Ascomycota

• Class: Dothideomycetes

• Order: Capnodiales

• Family: Mycosphaerellaceae

• Genre: cercospora

The fungus mainly attacks soybeans (Glycinemax), although other legumes may also be susceptible to a lesser extent.

Symptoms of the disease are easily identifiable on infected plants. The leaves present irregular reddish-brown, purple or purple spots, often with poorly defined edges. These spots may coalesce, leading to widespread necrosis and early defoliation of the plants.

Additionally, infected seeds exhibit purple or dark spots on the shell, which can compromise their quality and viability.

The reduction in functional leaf area directly affects the photosynthetic process, resulting in reduced grain filling and a drop in productivity.

The fungus survives in infected crop residues in the soil and in contaminated seeds, remaining latent until favorable environmental conditions allow its activation.

Under high relative humidity and moderate temperatures (between 20°C and 30°C), the fungus begins to produce conidia, asexual reproductive structures that are spread by wind, rain or agricultural equipment. These conidia germinate on the surface of plants, forming appressoria that penetrate plant tissues through stomata or directly through the cell wall.

The morphological characteristics of the fungus are typical of the genus cercospora.

Conidia are hyaline, filiform and multicellular, with regular transverse septa, while conidiophores are cylindrical and emerge in dense groups. The mycelium grows intercellularly in plant tissues, forming networks that facilitate the absorption of nutrients from the host.

During colonization, the fungus secretes degradative enzymes, such as cellulases and pectinases, in addition to specific toxins, such as cercosporin, which induce oxidative damage in plant cells, causing necrosis and tissue death.

The interaction between Cercospora kikuchii and soybeans are highly specific. The fungus has genes that encode effector proteins, responsible for manipulating the host's metabolic and signaling processes, suppressing its immune responses. Despite this, some soybean cultivars have genetic resistance that can confer tolerance to infection.

However, the genetic variability of the fungus can lead to the emergence of more aggressive breeds, overcoming this resistance over time.

To control Cercospora kikuchii, it is essential to adopt an integrated management that combines several agricultural practices. The use of certified seeds treated with specific fungicides is essential to prevent the introduction of the pathogen.

Crop rotation and proper management of crop residues help reduce the infectious load in the soil. Regular monitoring of crops allows early disease outbreaks to be identified and preventive measures to be taken.

In cases of severe infection, the application of fungicides based on strobilurins, triazoles or carboxamides may be effective, but must be carried out rationally to avoid the development of resistance. (Click here to see the pesticides registered for the control of "Cercospora kikuchii")

Cultural practices, such as adequate plant spacing and irrigation management, are also important to improve air circulation and reduce leaf wetness.