Background and Aims:

The species of algae that integrate the genus Cephaleuros induce diseases in more than 300 plant species worldwide. In Mexico, only Cephaleuros virescens has been identified infecting avocado, guava, lemon and mango leaves. In blackberry cultivation, only have been reported in the United States of America. This work aimed to identify the causal agent of the disease "orange spot" that affects blackberry plants (Rubus sp. cv. Tupy) in two areas of Michoacán, which represents a phytosanitary and ecological problem due to the agrochemicals used to combat it.

Methods:

To identify the causal agent, tissue from infected stems was examined for structures. Measurements were compared with data from related species: C. diffusus, C. parasiticus, and C. virescens. In addition, molecular data were integrated by extracting DNA from tissue of orange spots collected in the field at two sampling sites, amplification of the ITS and 18S DNA regions was performed and the sequences obtained, together with sequences of Cephaleuros from America, South Africa, and Asia from GenBank, were integrated into a data matrix for phylogenetic analyses.

Key results:

Following morphological and molecular analyses, C. virescens sensu lato (s.l.) was identified as the causal agent of the spots spreading along blackberry stems, mainly on third- and fourth-year plants. To date, C. virescens had only been reported on blackberry stems in the southeastern United States of America.

Conclusions:

Orange spotting on blackberry canes is caused by the alga Cephaleuros virescens (s.l.). This represents the first report of this species affecting blackberry in Mexico. Following phylogenetic analyses, it has been concluded that this is the same species that causes the disease on blackberries in the United States of America.

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