Abstract

RAYA-PEREZ, Mario et al. Isolation, characterization and pathogenicity of fungi causing descending death of American Black Walnut. Rev. Mex. Cienc. Agríc [online]. 2018, vol.9, n.5, pp.1061-1066. ISSN 2007-0934.  https://doi.org/10.29312/remexca.v9i5.1509.

American black walnut (Juglans nigra L.) is affected by phytosanitary problems, highlighting fungi that cause cankers in branches, reducing fruit production up to 60% of the average yield that is 1.9 t ha-1. The objectives of this investigation were to identify the fungi associated with cankers present in branches of trees of J. nigra with symptoms of descending death and to evaluate their pathogenicity. Canker fungi were isolated from branches with symptoms of descending death collected in two orchards of the state of Coahuila. Four fungal morphotypes were obtained and one strain of each was used for its morphological identification at the genus level, and by sequencing the ITS1 region to ITS2 of the ribosomal genes (rDNA) for its identification at the species level. Pathogenicity tests were performed on four-month-old J. nigra seedlings, making a 3 mm long stem fissure and inoculating with each identified species. The fungi associated with the cankers of J. nigra were morphologically identified as members of the genera Trichothecium, Pestalotiopsis, Alternaria and Rhizoctonia. By means of the BLAST analysis in the GenBank of the sequences of the ITS1 to ITS2 region it was possible to determine that the strains were related to the species Trichothecium roseum, Pestalotiopsis steyaertii, Alternaria alternata and to an undetermined binucleate species of Rhizoctonia. The inoculation of the four strains to seedlings showed that they are pathogenic to J. nigra.

Keywords : Alternaria alternata; Pestalotiopsis steyaertii; Rhizoctonia binucleada; Trichothecium roseum; fungi in cankers.

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