First report of Cladosporium cladosporioides causing leaf spot on tomato in Mexico

Abstract

During 2017, a severe leaf spot disease was observed in atomato greenhouse in Texcoco, Estado de México, Mexico.Symptoms on leaves included yellow irregular lesions on adaxialsurfaces, whereas intense grayish brown sporulation developedon the undersides of the lesions. Disease incidencewas approximately 35%. The pathogen was isolated on PDAmedium and colonies exhibited sparse aerial mycelium,olivaceous-brown to brown, with a velvety texture and sporulationprofuse. Conidiophores were solitary, straight toslightly flexuous, olivaceous-brown, narrowly cylindrical tosubcylindrical-oblong, occasionally once geniculate, unbranchedor occasionally branched, and measuring 40?300 × 2.5?3.5 μm. Conidia were catenated, in long branchedchains, olivaceous-brown, smooth. Intercalary conidia werelimoniform or sometimes subcylindrical, aseptate, of 5?12.5 × 1.8?2.4 μm. Secondary ramoconidia were aseptate oroccasionally 1-septate, ellipsoid, cylindrical-oblong, of 12?15 × 2.5?3.5 μm. Based on morphological features, the funguswas identified within the Cladosporium cladosporioidesspecies complex (Bensch et al. 2012). An isolate was depositedin the Culture Collection of Phytopathogenic Fungi of theChapingo Autonomous University as UACH293. For molecularidentification, the ITS region and part of EF1-α gene wereamplified by PCR and sequenced using the primer sets ITS5/ITS4 and EF1-728F/EF1-986R, respectively. The sequenceswere deposited in GenBank (Accession Nos. ITS:MH785190and EF1-α:MH785189). A phylogenetic analysis usingBayesian inference and including published ITS and EF1-αsequence dataset for Cladosporium species was performed.The phylogenetic analysis resulted in a well-supported cladegrouped with the type species of C. cladosporioides. To verifythe pathogenicity of the fungus, inoculations were performedon 20 leaves of two-month-old tomato plants by spraying aconidial suspension (105 spores/ml). Five leaves were mockinoculated with distilled water as a control. Symptoms of leafspots were produced 10 days after inoculation, whereas thecontrol leaves remained healthy. Cladosporiumcladosporioides has been reported associated with tomato inBrazil, China, and Malaysia (Farr and Rossman 2018). To ourknowledge, this is the first report of leaf spot on tomato causedby Cladosporium cladosporioides in Mexico.