Belinda Rawnsley

Diaporthe perjuncta Does Not Cause Phomopsis Cane and Leaf Spot Disease of Grapevine in Australia

In Australia, Diaporthe perjuncta (formerly known as Phomopsis taxon 1) and Phomopsis viticola (Phomopsis taxon 2) have been associated with Phomopsis cane and leaf spot of grapevine. Although P. viticola causes distinct leaf spots, as well as lesions on shoots and canes, the pathogenicity of D. perjuncta is relatively unknown. The pathogenicity of D. perjuncta and P. viticola was studied in relation to symptom expression and bud loss. Only P. viticola caused brown-black, longitudinal, necrotic lesions on stem tissue and leaf spots characteristic of the disease, whereas both D. perjuncta and P. viticola induced bleaching of dormant canes. Inoculation of dormant buds with D. perjuncta did not cause bud death. D. perjuncta and P. viticola were reisolated from inoculated tissue and into pure culture. D. perjuncta colonized the epidermis and cortex of the grapevine shoot but not the vascular tissue. D. perjuncta appears to be an endophyte, rather than a pathogen of grapevine.

The role of Diaporthe perjuncta in delayed budburst and death of grapevine buds

Diaporthe perjuncta has been associated with Phomopsis cane and leaf spot disease of grapevine in Australia. Both D. perjuncta and Phomopsis viticola cause bleaching of cane and, for this reason, diagnosis of the two fungi is often confused in the vineyard. P. viticola causes leaf spots and shoot lesions in the growing season, whereas more recent studies have indicated that D. perjuncta might not be a pathogen. Field studies were conducted to assess the role of D. perjuncta in delayed budburst and death of grapevine buds. Over three seasons (1999–2001), vines were assessed at four vineyards in South Australia for percentage of budburst and incidence of D. perjuncta. A D. perjuncta-specific probe, pT1P180, was used to detect D. perjuncta in unburst buds, cane and shoots on spurs having buds that failed to burst. D. perjuncta was detected in both bleached and non-bleached cane. Although there was a significant association between the incidence of D. perjuncta and buds that failed to burst in 1999 only, overall bud burst was normal in all vineyards and bud loss was not a concern. Bunch number and shoot growth was not affected. Mites were considered as a possible factor in damage to unburst buds, but it was more likely that failure of buds to burst was related to physiological or environmental effects. D. perjuncta did not adversely affect grapevine productivity and cannot be regarded as a pathogen of grapevine.