Biological control approach of Ailanthus altissima in Lombardy

Ailanthus altissima Mill. Swingle, a deciduous tree of Chinese origin, has become invasive in many nations of North America and Europe, spreading worldwide both in urban and natural ecosystems. Neither mechanical nor chemical techniques have demonstrated to be fully effective in its management, therefore, biological control is considered to be a promising approach. With the aim of setting a potential biological control strategy of A. altissima, several fungal strains associated with wilting or decaying ailanthus trees grown in different areas of Lombardy were isolated from their woody tissues. Colony characteristics were recorded and presence of reproductive structures was described by optical microscopy observations. Ten morphotypes were finally isolated and purified. A preliminary identification at the genus level was conducted on 34 representative strains by sequencing ITS region confirming morphological observations. Two fungal strains belonging to the genera Fusarium and Verticillium were selected and pathogenicity tests were carried out on A. altissima plants grown in pots from seeds and on more than one-hundred adult trees distributed in five different woody areas of the territory crossed by the Brembo and Adda rivers. Fusarium sp. and Verticillium sp. induced decay symptoms to 35% and 90% of treated plants, respectively. Symptoms on seedlings appeared few weeks after inoculation while the decline on adult plants was evident after the new budding in the spring following inoculation. A detailed genomic identification and taxonomic description of the two strains is ongoing.