Investigation into the cause of rootstock necrosis in grapevine nurseries
Objectives & Rationale
Rootstock necrosis of grafted nursery vines (i.e. dead zones primarily at the base of rootstocks) has been identified in several Vine Improvement Association (VIA) reports as a major cause of rejections in grapevine nurseries. The objectives of this project would therefore be:
(1) to determine which fungi or fungal complexes are associated with rootstock necrosis;
(2) to determine whether these infections are the cause of the symptoms or if other factors predispose the rootstocks to fungal infections;
(3) to graft rootstock cuttings with discolorations on one side in order to determine whether this is the cause of the symptoms observed.
Surveys were conducted in grapevine nurseries by collecting nursery vines with typical symptoms. Fungal isolations were conducted in the laboratory to determine if specific pathogens could be associated with these symptoms. Other factors that could contribute to the development of these specific symptoms were also investigated. Consequently, dormant rootstock shoots which are used as grafting material were also included in the study. Field trials were also conducted to see whether these specific symptoms could be recreated and which factors contribute to symptom development.
The most affected rootstocks included Ramsey, Richter 110, US8-7, followed by Paulsen 1103, Ruggeri 140, Richter 99, 143B Mgt, 101-14 Mgt and SO4. Rootstocks cuttings with discolorations on the one side that are used as grafting material was identified as a possible predisposing factor. Several grapevine trunk disease pathogens were isolated from both of these types of material. However, based on the knowledge of the pathogens isolated and the symptoms they are associated with, it is highly unlikely that any of these pathogens are the primary cause of these specific symptoms and that they merely infect plant material that was predisposed by other factors. Rootstock cuttings with discolorations on the one side and rootstocks from grafted vines with necrotic lesions at the base were traced back to several sources. Field trials were conducted with rootstock material from one of these sources. At the end of the nursery season typical rootstock necrosis (dead parts at the base of rootstocks) with no root formation on one side was observed in all three combinations. Discolorations in or on the one side of the rootstock prior to grafting was not a prerequisite as only 18.2% of such vines developed necrosis (typical symptoms). The only other observation that stood out was the position of the basal bud/side-shoot where 64% of the rootstocks with rootstock necrosis had basal buds 5-20 cm away from the base of the rootstock
It is recommended that nurseries adhere to the physical requirements for plant material (Vine Improvement Association) to ensure that a node is within 15 mm of the base of each rootstock. Rootstock cuttings with internal discolorations should not be grafted as these cuttings will most likely die in the nursery contributing to the low percentage certifiable vines produced in local nurseries.
Moyo, P, Mostert, L and Halleen, F. 2013. Investigation into the cause of poor budburst and dying single spurs in Sauvignon blanc and Cabernet Sauvignon. Paper presented at the 35th South African Society for Enology and Viticulture Conference. 13-15 November, Somerset West, South Africa.
Moyo, P, Mostert, L and Halleen, F. 2014. Spur dieback in young Sauvignon blanc and Cabernet Sauvignon vineyards: Results from recent surveys. Paper presented at the 36th South African Society for Enology and Viticulture Conference. 12-14 November, Somerset West, South Africa.
Halleen, F. 2013. Resistance and soilborne plant diseases. Grapevines – are we making progress? Paper presented at the 23rd Soilborne Plant Diseases Symposium. 18-19 September, Stellenbosch, South Africa.
Langenhoeven, S, Halleen, F. and Mostert, L. 2013. Detection and quantification of soil borne pathogens in grapevine nurseries. Paper presented at the 36th South African Society for Enology and Viticulture Conference. 12-14 November 2014, Somerset West, South Africa.
Halleen, F. 2013. Investigation into the cause of rootstock necrosis in grapevine nurseries. Paper presented at the 36th South African Society for Enology and Viticulture Conference. 12-14 November, Somerset-West, South Africa.