FIRST REPORT OF LEAF RUST CAUSED BY MELAMPSORA MAGNUSIANA ON POPULUS ALBA IN ITALY

Abstract

In October 2016, Melampsora spp. hypophyllous uredinia (0.3-0.5 mm in diameter) were observed on leaves of Populus alba L. clones cultivated in Casale Monferrato at CREA-PLF (Piedmont, northern Italy). Morphological observations and DNA sequencing of the Internal Transcribed Spacer (ITS) region were performed to identify the fungus at the species level. Urediniospores were yellowish, obovate, verrucose and on average 23.3 x 18.8 µm (wall 1.22-2.44 µm thick). DNA was extracted from urediniospores with the Quiagen Plant DNeasy Mini-kit following manufacturer’s instructions. The ITS region was amplified and sequenced with taxon selective primers ITS1-F and ITS4-B (Gardes and Bruns, 1993). Sequences were deposited in GenBank (accession Nos. KY364897, KY364898) and compared with those of known Melampsora species using the NCBI GenBank nucleotide BLAST search. Based on morphological features of uredinia and urediniospores and DNA sequences the fungus was identified, according to Vialle et al. (2011), as Melampsora magnusiana G.H. Wagner, belonging to M. populnea complex and associated with P. alba, P. tremula L. and P. x canescens (Aiton) Sm. telial hosts. The identification of this Melampsora species was also supported by the presence of its known aecial hosts Chelidonium majus L. and Corydalis spp. in the neighborhood of the sampling site (Picco, 2010). Telia were not observed. Disease symptoms consisting of chlorotic spots were reproduced on the abaxial surface of ten leaves cut from five P. x canescens, belonging to the same clone, artificially inoculated by spraying a spore suspension of the fungus (105 spores ml-1 ). Uredinia were observed ten days after inoculation. Non-inoculated leaves remained symptomless. To our knowledge, this is the first report of M. magnusiana on P. alba in Italy, although it was observed in some European countries (Pei and McCraken, 2005) on both Populus spp. and aecial hosts.