Abstract
Arbutus unedo L. is an ecologically and economically important Mediterranean evergreen shrub or small tree, increasingly used in restoration and ornamental plantings. Despite its significance, its diseases and associated pathogens remain poorly studied. Phytophthora cinnamomi, one of the world’s most destructive plant pathogens, represents an emerging threat to Mediterranean ecosystems but has not previously been reported on A. unedo in Italy. In recent years, dieback has been observed in natural populations near Monticiano, Tuscany, while similar symptoms, associated with extensive mortality, have occurred in commercial nurseries in the Pistoia district. Woodland plants showed reduced vigour and hook-shaped shoot tips, whereas nursery plants exhibited root rot, collar necrosis, leaf chlorosis, crown dieback, wilting, and death. A total of 184 oomycete isolates were consistently recovered from symptomatic roots and collars and from rhizosphere soil. Morphological characterization and multilocus molecular analyses identified the isolates as P. cinnamomi. The pathogenicity of the oomycete was demonstrated by artificially inoculating healthy A. unedo seedlings, which displayed symptoms very similar to those observed under field conditions. Both representative isolates caused severe disease, resulting in 100% mortality of inoculated plants within 30 days, whereas no mortality occurred in control plants. Re-isolation of the pathogen from inoculated tissues fulfilled Koch’s postulates. These findings constitute the first report of P. cinnamomi on A. unedo in Italy and raise concern about its possible spread in natural ecosystems and through nursery production and trade.