Quantification of Soilborne Pathogens in Grapevine Nurseries

Project Number
US PP LM 02 2012

Project title
Quantification of Soilborne Pathogens in Grapevine Nurseries

Project leader
Mostert, L

Institution
University of Stellenbosch. Faculty of AgriSciences. Department of Plant Pathology

Team members
Mostert, L
Halleen, F
Langenhoven, S
Vermeulen, C
Marais, J
Lesuthu, P

Completion date
2016

Project description
The DNA of black foot and crown and root rot pathogens were detected with qPCR in the soil of the five nurseries investigated in 2013, 2014 and 2015. Isolations from nursery grapevines confirmed the presence of these pathogens in the 2013 and 2015 grapevine sampling from four of the five nurseries. This is the first study to confirm the presence of black foot and crown and root rot pathogens with qPCR in grapevine nursery soils.
Of the different rotation crops investigated only Triticale (5 plants) and forage radish (1 plant) harboured black foot and crown and root rot pathogens. Canola, white mustard and lupins did not have any of these pathogens. A variety of weeds including corn spurry, rye grass, winter grass, Cape marigold and Johnson grass had black foot and crown and root rot pathogen infections.
The presence of the pathogen DNA in the soil as well as pathogen presence in grapevine plants shows that pathogen inoculum persist in the soil during the crop rotation year. The DNA concentrations in the crop rotation year (2014) were for Dactylonectria and Ilyonectria species as well as Phytophthora species equal or more than in the first grapevine year (2013) investigated. Together with the fact that the DNA concentrations for these pathogens were higher in the second grapevine year investigated (2015) indicate that the pathogens survive successfully in the soil or in the roots and basal ends of specific weeds and rotation crops. It is known that Dactylonectria, Ilyonectria and Phytophthora species form chlamydospores, which are hardened survival structures allowing these fungi to persist in soil. Pythium species are generally homothallic and can form sexual oospores that can survive in the soil.
Soil not cultivated with grapevine nursery plants for a long period of time as well as a three-year rotation system were both characteristics of the nursery with the lowest pathogen DNA detected in the soil and vines with no pathogen infection. Black foot pathogens isolated from grapevines include: Dactylonectria alcacerensis, Dactylonectria macrodidyma, Dactylonectria novozelandica, Dactylonectria pauciseptata, Dactylonectria torresensis, Ilyonectria liriodendri, Campylocarpon fasciculare and Campylocarpon pseudofasciculare. One Dactylonectria and one Ilyonectria species are putative new species. This is the first report of Dactylonectria alcacerensis and D. pauciseptata on grapevines in South Africa.
Of the crown and root rot pathogens: Pythium irregulare, P. sylvaticum, P. ultimum, P. heterothallicum, P. rostratum, Py. vexans, and Ph. niederhauserii were isolated. Phytopythium helicoides and Py. litorale were also isolated from grapevines in nurseries and vineyards, but their pathogenicity toward this crop has not been determined. Pythium sylvaticum was isolated from nursery vines for the first time since 1980. Only one Phytophthora isolate (Ph. niederhauserii) was obtained in 2013. The low occurrence of Phytophthora species in nursery vines can be contributed to the application of fosetyl-Al and metalaxyl based fungicides for the control of downy mildew. Since nursery vines get infected with black foot and crown and root pathogens present in nursery soils, the most viable solution is hot water treatment of nursery vines.
A new species of Phytopythium was found from a single nursery grapevine. Phytopythium paucipapillatum sp. nov. was morphologically described and phylogenetic analyses of the ITS and CO1 genes were conducted. A pathogenicity trial was conducted on the grapevine rootstock 110-Richter.The trial results reveal that this species is non-pathogenic and may therefore be a saprophytic soil inhabitant. The glasshouse based bioassay to correlate pathogen DNA concentration in the rhizosphere soil with disease expression was not successful. Reliable inoculation concentrations and methods causing disease first need to be determined to be able to get an optimal bioassay system in which the pathogen DNA concentration in the rhizosphere soil can be correlated with disease.

Poster(s)
Langenhoven, S D, Halleen, F and Mostert, L. 2015. Detection and quantification of soilborne pathogens in grapevine nurseries. Poster presented at the 49th Congress of the Southern African Society of Plant Pathology, 18-21 January 2015, Bloemfontein, South Africa.

Presentation(s)
Langenhoven, S, Halleen, P and Mostert, L. 2013. Quantification of soil borne pathogens in grapevine nurseries: An update. Paper presented at the 35th South African Society for Enology Conference. 13-15 November, Somerset West, South Africa.

Langenhoven, S D, Halleen, F and Mostert, L. 2014. Detection and quantification of soil borne pathogens in grapevine nurseries. Paper presented 36th South African Society for Enology Conference. 12-14 November, Somerset West, South Africa.

Langenhoven, S D, Halleen, F and Mostert, L. 2015. A new species of Phytopythium found from grapevine roots in South Africa. Lecture. Friday Forum, University of Stellenbosch, Faculty of AgriScience, Department Plant Pathology. 3 July, Stellenbosch, South Arica

Langenhoven, S D, Halleen, F and Mostert, L. 2016. A survey of soil borne grapevine decline pathogens in nurseries. Lecture. Friday Forum, University of Stellenbosch, Faculty of AgriScience, Department Plant Pathology. 20 May, Stellenbosch, South Africa.

Langenhoven, S D, Halleen, F, Mostert, L. 2016. A survey of soilborne grapevine decline pathogens in nurseries. Paper presented at the 38th South African Society for Enology and Viticulture Conference. 23-25 August, Somerset West, South Africa.

Langenhoven, S D, Halleen, F, Mostert, L. 2017. Detection and quantification of black foot pathogens in grapevine nursery soil, rotation crops and weeds in South Africa. 10th International Grapevine Trunk Disease Workshop. 4-7 July, Reims, France.

Publications

Langenhoven SD, Halleen F, Spies CFJ, Stempien E, Mostert L. 2018. Detection and quantification of black foot and crown and root rot pathogens in grapevine nursery soils in the Western Cape of South Africa. Phythopathologia Mediterranea 57: 519-537. DOI: 10.14601/Phytopathol_Mediterr-23921

Langenhoven SD, Spies CFJ, Halleen F, Mostert L. Phytopythium paucipapillatum sp. nov. isolated from nursery grapevines in South Africa. Article in preparation. Submitted to Mycological Progress.

Langenhoven SD, Halleen F, Spies CFJ, Stempien E, Mostert L. 2018. Detection and quantification of soilborne pathogens in grapevine nurseries. SATI Technical bulletin August, pp. 19-20.

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