Population structure of Valsa ceratosperma, causal fungus of Valsa canker, in apple and pear orchards

On the basis of mycelial compatibility, the population structure of Valsa ceratosperma, the causal fungus of Valsa canker on broadleaf trees, was investigated in apple and pear orchards in Japan. Field strains of V. ceratosperma from a single canker on trunks or scaffold limbs belonged to different mycelial compatibility groups. Thus, the population structure of this fungus was complex in most orchards. Because mycelia of strains originating from different conidia from the same pycnidium were compatible, infection by this fungus is thought to be ascospores.