The first global case of wire-burning disease in cassava was registered by the Brazilian Agricultural Research Corporation (Embrapa) in Brazil. Molecular and biological analyses identified the fungus, Rhizoctonia solani AG-1 IA, which attacks the aerial part of the plant, in crops in the municipality of Mâncio Lima, in the Juruá region, which produces the most cassava in the state of Acre.
The discovery was published in the Australasian Plant Disease Notes magazine. With this identification, coordinated by a researcher at Embrapa, Acre Amauri Siviero, it is now possible to advance the research for the genetic improvement of the culture and the recommendation of effective disease control measures.
“In field expeditions, we found that some 10% of the plants in the fields reported burning characteristics in the foliage. From samples of infected materials collected in different cultures, we performed pathogenicity tests for the characterization and reproduction of disease symptoms in the laboratory. Based on the isolated material, molecular and biological analyses were conducted to identify the fungus (pathogen). The results allowed us to conclude that this disease has never been reported in any cassava crop in any country,” said Siviero.
In Brazil, the fungus, Rhizoctonia solani AG-1 IA, was identified as it attacks crops such as beans, coffee, rice, potatoes, soybeans, corn and rubber, among others, always associated with the burning and rotting of certain parts of the plant (roots, leaves and seeds). Its main form of dissemination is through the wind.
“The burning of cassava causes the necrosis of branches and leaves that darken, dry and burn, as if a flamethrower had passed through the fields. The symptoms of the disease evolve rapidly and the injured leaves detach from the stem and are hung by a white thread, which is the body of the fungus itself,” explained Siviero.
“Due to the predominance of outbreaks alongside forest extensions, we believe that the fungus may have migrated from the host plants, from the interior of the forest, to the crops. Another hypothesis is that this pathogen has undergone a specialization process as part of the natural process of evolution to adapt to new hosts,” said the scientist.