First Report of Phytophthora mengei Causing Root Rot and Canker in Avocado (Persea americana) in Michoacán, Mexico

Mexico is the world's leading producer of avocado (<i>Persea americana</i>); however, its productivity is threatened by various diseases, especially root rot caused by <i>Phytophthora</i>. While <i>P</i>. <i>cinnamomi</i> is the most commonly reported species worldwide, this study identified <i>P</i>. <i>mengei</i> for the first time as a causal agent of root rot and trunk canker in avocado orchards in the state of Michoacán, México. The morphological and molecular characterization of four isolates (three from canker and one from root rot) confirmed their identity: semi-papillate sporangia and plerotic oospores with paragynous antheridia, with sequence identities of 99.87% (<i>ITS</i>) and 100% (<i>COI</i>) with type sequences of <i>P</i>. <i>mengei</i>. Pathogenicity tests demonstrated the ability to infect roots, stems, and fruits, although with a low reisolation percentage in roots (10%), suggesting an opportunistic pathogen behavior. Sensitivity tests to potassium phosphite (EC₅₀ of 3.67 μg/mL^-1 a.i.) and metalaxyl-M (0.737 μg/mL^-1 a.i.) revealed possible limitations for chemical control. These findings position <i>P</i>. <i>mengei</i> as an emerging pathogen with important implications for integrated crop management. To the best of our knowledge, this is the first report of <i>P</i>. <i>mengei</i> causing root rot and trunk canker in avocado in Michoacán, Mexico.