Genetic diversity in Dactylonectria pauciseptata associated with black foot disease in New Zealand

Abstract

The fungal genera Ilyonectria and Dactylonectria are causal agents of black foot disease affecting grapevines. A New Zealand survey of grapevines symptomatic for this disease was conducted in 2005, and 11 D. pauciseptata isolates were recovered. The incidence of this disease has increased over the last decade so a multi-gene approach was used to accurately identify these isolates and to determine whether they could infect grapevine roots in vitro. Eight of the original 11 D. pauciseptata isolates remained viable and were recovered from storage. DNA sequencing, universally primed polymerase chain reaction (UP-PCR) and a detached root assay were used to characterise these eight isolates. Phylogenetic analyses of ITS, β-tubulin, EF1-α and histone gene regions showed a monophyletic clade using the rRNA gene, EF1-α and histone gene, but paraphyletic based on β-tubulin. UP-PCR showed genetic diversity, with five major groups (P<0.01), with major groups concordant with the β-tubulin phylogeny. Pathogenicity tests with two common rootstocks showed that isolates produced lesions. Two distinct groups of D. pauciseptata were identified. Both groups are capable of infecting grapevine roots.