The infection process of Armillaria mellea and Armillaria solidipes

Armillaria mellea and A. solidipes are two of the primary causal agents of Armillaria root rot (ARR) in over 500 woody hosts. Although extensive research on this disease has been conducted over the past few decades, finding controls for ARR has been challenging. This is largely due to the lack of knowledge of the fungal infection and host response processes. It is important to understand the infection process in order to develop new strategies to control the disease. In this review, the initial steps of the infection process of A. mellea and A. solidipes are discussed, with focus on fungal attachment and penetration. A mucilaginous substance produced at the rhizo-morph tip is thought to aid attachment of the pathogen to host. Toxins and cell wall degrading enzymes produced by the fungus together with mechanical pressure generated by the rhizomorph is speculated to support fungal penetration. However, a detailed description of the Armillaria spp. infection process is lacking in the literature, and this illustrates the need for further studies.