|Spies, C - STELLENBOSCH UNIV., S.A.|
|Mcleod, Adele - STELLENBOSCH UNIV., S.A.|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 1, 2006
Publication Date: July 1, 2006
Citation: Spies, C.F.J., Mazzola, M., Mcleod, A. 2006. Characterization of pythium and phytophthora species associated with grapevine decline in South Africa. Proceedings, 44th Congress of the Southern African Society for Plant Pathology. p. 62. Technical Abstract: Replant and decline diseases of grapevine are causing economic losses due to a reduction in quantity and quality of grapes, as well as costs incurred when vineyards have to be replanted prematurely. The specific factors contributing to replant and decline diseases have been poorly addressed, except for the contribution of trunk diseases. Pythium species are often isolated from diseased vines, suggesting that they could be involved in the destruction of feeder roots, and thus contribute to decline. Therefore, the aim of this study was to indentify which Pythium spp. are associated with grapevines exhibiting decline symptoms. Additionally, the possibility that pathogenic Pythium species are distributed through nursery grapevines was also investigated by conducting surveys in grapevine nurseries. Surveys were conducted in five grapevine nurseries (4 climatic regions) in February/March 2005, as well as in 30 established vineyards (10 climatic regions in February/March, July and September/October 2005. In the nurseries, Pythium species were recovered from the roots as well as the crown region of plants, whereas in older vineyards isolates were obtained only from fine feeder roots. Baiting of Pythium was performed on some of the soils. Pythium species that were obtained through isolations were identified to the species level through sequence analyses of the internal transcribed spacer 1 (ITS1) and ITS2 region. Pythium apecies that were indentified among 44 nursery isolates included P. vexans, P. ultimum var. ultimum and P. irregulare. Among the Pythium species recoved from nursery plants some were isolated from both crowns and roots (P. vexans), whereas other species were isolated only from crowns (P. ultimum var. ultimum) or roots (P. irregulare). The Pythium isolates collected from roots of established vines included P. irregulare and P. heterothallicum. The selection of isolates from the soil included known pathogens such as P. ultimum var. ultimum, P. irregulare, P. sylvaticum and P. vexans. In previous studies P. ultimum, P. irregulare, and P. sylvaticum have been shown to cause substantial root rot of grapevines in South Africa. There are no previous reports of P. vexans and P. heterothallicum isolated from grapevines in South Africa, and their pathogenicity therefore needs further investigation.