Re-evaluation of pathogens causing Valsa canker on apple in China.

Valsa canker is a destructive disease on apple that causes serious economic losses in eastern Asia. In the present study fungal isolates from cankered apple and pear bark were examined and compared with morphology and rDNA-ITS sequences. Valsa mali was confirmed to be an independent species and a causal pathogen of Valsa canker on apple and pear in China. It was the predominant species (96.7% of isolates) on apple and was complemented by V. malicola (3.3% of isolates). Significant intraspecific genetic differentiation was detected in V. mali with two varieties recognized, V. mali var. mali occurring exclusively on apple and V. mali var. pyri occurring on both apple and pear. Results from genetic analysis and cross-inoculation tests provided support for the hypothesis that host preference probably catalyzed such genetic changes within the pathogen populations.