Species of Phomopsis and a Libertella sp. occurring on grapevines with specific reference to South Africa: morphological, cultural, molecular and pathological characterization

Abstract

In order to clarify the taxonomy of species of Phomopsis associated with grapevines, 61 isolates were obtained from 58 different vineyards in the grapevine growing areas of the Western Cape province of South Africa. Species delimitation was primarily based on alpha conidium and conidiophore morphology, cultural characteristics, pathogenicity to Vitis vinifera, and the ability to form the teleomorph in vitro. The identity of each taxon was confirmed by means of phylogenetic analyses of the nuclear ribosomal DNA internal transcribed spacers (5.8S, ITS1 and ITS2) and the 5’ end partial sequence of the mitochondrial small subunit (mtSSU). We also re-examined the four taxa that previously had been associated with grapevines in Australia. Three of the latter taxa, and a Phomopsis species commonly associated with shoot blight of peaches in the USA, P. amygdali, were identified among the South African isolates. Phomopsis amygdali was isolated once only and appeared to be of lesser importance in this disease complex. Furthermore, Diaporthe perjuncta and Phomopsis sp. 1 were also rarely encountered and proved to be nonpathogenic, indicating their nonfunctional role in Phomopsis cane and leaf spot disease. Phomopsis viticola was common and widely distributed throughout diseased vineyards. This taxon was associated with the typical cane and leaf spot disease symptoms and proved to be highly virulent. Morphologically collections designated in previous studies as taxon 2 corresponded best with P. viticola, which was also neotypified in this study. Examination of the Australian culture designated as taxon 4 revealed it to be a species of Libertella, thus excluding it from the P. viticola complex. An Italian isolate was found to represent a species of Phomopsis not previously known from grapevines, and this was subsequently designated as Phomopsis sp. 2. A key to taxa of Phomopsis from grapevine is also provided.