Japanese pear black spot and apple alternaria blotch

The pathogenicity and taxonomy of 15 isolates ofAlternariaspp. from pear and apple were compared. Only isolates from Asian pear (Pyrus pyrifolia) from Italy and Korea were virulent on leaves and young fruits of the susceptible Asian pear cv. Nijisseiki. Their conidial morphology was typical ofA. gaisen(=A. kikuchiana). Only isolates ofA. malifrom USA were virulent on susceptible American apple cvs Indo and Red Gold. No virulence was demonstrated in any isolate/host combination among isolates from stem infections of Asian and European pear (Pyrus communis), leaf spots of European apple, and ripe fruit rots of Chinese pear (Pyrus ussuriensis), European pear and apple. These non‐virulent isolates could be readily distinguished fromA. gaisenandA. maliby their pattern of branching of conidial chains, the branching associated withA. alternata sensu strictobeing most common among non‐virulent isolates. This limited survey implies thatA. gaisenis only virulent to Asian pear and the toxigenic form ofA. malito certain American apple cultivars; also thatA. gaisenis not established outside eastern Asia or the toxigenic form ofA. malioutside eastern Asia and parts of USA.