Molecular detection of Phomopsis taxa 1 and 2 in grapevine canes and buds.

DNA sequences, specific to each of the two taxa of Phomopsis (taxon 1 and taxon 2) that commonly infect grapevines in Australia, have been identified and cloned. The clones recognise a repeated sequence and both identify genetic variation. The taxon 2-specific marker identified five distinct banding patterns amongst twelve Phomopsis taxon 2 isolates obtained from five different geographical regions. The Phomopsis taxon 1-specific clone was used to detect the fungus in canes and unburst buds of grapevines that displayed symptoms of infection, visible in late winter as pycnidia on bleached canes. However, the fungus was also detected in canes and unburst buds from canes that were not bleached. In addition, perithecia of the sexual phase were observed on other unburst buds following incubation of canes. The results suggest that bleaching should not be used as an indicator of infection by Phomopsis taxon 1. Microscopic examination of infected, micropropagated grapevines showed that, similar to other Phomopsis species, taxon 1 grows subcuticularly in the stems. The specificity and high copy number of the taxon 1 and taxon 2 probes, together with a rapid DNA extraction method, provide the means for a sensitive assay for these fungi and for fundamental studies on the biology of two Phomopsis taxa that infect grapevine in Australia. [ABSTRACT FROM AUTHOR]