First Report of the Armillaria Root-Disease Pathogen, Armillaria gallica, Associated with Several Woody Hosts in Three States of Central Mexico (Guanajuato, Jalisco, and Michoacan)

In July-August 2019, seven Armillaria isolates (derived from rhizomorphs and mycelial fans of infected roots) were collected in association with woody hosts in the central Mexico: states of Guanajuato (MEX204), Jalisco (MEX206, MEX208, MEX209), and Michoacan (MEX211, MEX214, MEX216). All seven isolates were identified as Armillaria gallica based on translation elongation factor 1α (tef1) gene sequences (GenBank accession Nos.: MN839636 - MN839642 for MEX204, MEX206, MEX208, MEX209, MEX211, MEX214, and MEX216) and somatic pairing tests against known tester isolates. GenBank nucleotide BLAST results showed tef1 similarity for all isolates was highest for with A. gallica (≥ 97%; GenBank Accession Nos. KF156775 and KF156772). In replicated pairings against three tester isolates each for A. gallica, A. mellea, and A. mexicana, all isolates showed the highest compatibility with A. gallica (67-100%), with lower compatibility against A. mellea and A. mexicana, with 3-11% and 2-11%, respectively. Variations in compatibility among different tester isolates could reflect cryptic speciation within A. gallica (Klopfenstein et al., 2017). In Tarimoro, Guanajuato, MEX204 was isolated from infected Quercus jonesii (20°13'46.2"N 100°42'51.1"W, elevation 2286 m) that displayed root disease symptoms/signs (wilting/defoliation and mycelial fans within the roots). In a forested area of Mazamitla, Jalisco, MEX206 was isolated from infected Quercus laevis (19°54´52"N 103°00´07"W, elevation 2564 m) with root disease symptoms/signs (e.g., wilting, foliar chlorosis, and mycelial fans within the root crown); MEX208 was isolated from infected Pinus pseudostrobus (19°54´53"N 102°59´54"W, elevation 2554 m) with basal resinosis and mycelial fans; and MEX209 was collected from a symptomless P. devoniana (19°54'13.1"N 103°00'14.1"W, elevation 2566 m). In Zinapecuaro, Michoacan, MEX211 (19°53'28.8"N 100°39'44.0"W, elevation 2587 m) was isolated from infected Malus domestica with root disease that resulted in mortality; in Hidalgo, Michoacan, MEX214 (19°46'49"N 100°39'25.2"W, elevation 2961 m) and MEX216 (19°46'58"N 100°39'24"W, elevation 2958 m) were isolated from infected P. devoniana and P. teocote, respectively, which both displayed root disease symptoms/signs (basal resinosis and mycelial fans). Previously, A. gallica was reported in the State of Mexico, Veracruz, Oaxaca, Mexico (Elias-Roman et al. 2013; Klopfenstein et al. 2014), but this represents the first report of A. gallica in Guanajuato, Jalisco, and Michoacan, Mexico. In contrast to other regions of North America (e.g., Bruhns et al. 2000), A. gallica was demonstrated to be a virulent pathogen on peach (Prunus persica) in central Mexico (Elias-Roman et al. 2013). Unfortunately, tree seedlings cannot be used for Armillaria pathogenicity tests in a greenhouse or nursery; however, all root-diseased trees in this report showed Armillaria mycelial fans under the bark of a living tree, which are reliable indicators of pathogenicity, and no other root diseases were found. This report demonstrates that A. gallica is distributed across central Mexico, where it is associated with disease on Quercus, Pinus, and Malus. Such information is critical to increase our understanding of Armillaria root disease across diverse geographic regions and climates.