Identification of a New Source of Resistance to Anthracnose in Cucumber in Japan

Anthracnose, caused by the fungal pathogen Colletotrichum orbiculare, is one of the severest diseases in open-field cucumber (Cucumis sativus L.) cultivation in Japan. Genetically conferred host resistance is the best way to control anthracnose. In order to develop new cultivars resistant to anthracnose, identification of promising sources of resistance is vital. In this study, we screened 232 genetic resources of Asian origin preserved in the NARO Genebank and identified one accession, 'Ban Kyuri', with strong, although not perfect, resistance to anthracnose. Further evaluation of the resistance based on seedling and greenhouse assays confirmed resistance. We also revealed a wide variation in the virulence of three C. orbiculare strains in Japan. 'Ban Kyuri' exhibited stable resistance to all strains. Genotyping of CsSGR, a known gene for anthracnose resistance, indicated that 'Ban Kyuri' is homozygous for the wild-type allele, and its resistance level was equal to or higher than that of accessions harboring Cssgr, the mutated allele conferring resistance. This finding indicates that 'Ban Kyuri' harbors a novel resistance gene or a novel allele of CsSGR conferring anthracnose resistance. 'Ban Kyuri' is a promising new source of resistance to diverse anthracnose strains with different levels of virulence in Japan, and its use will help to further clarify the genetic mechanism of anthracnose resistance in cucumber.