The choice of rootstock is an important decision which can determine the success of your newly planted vineyard. Various aspects (it usually follows a process of elimination) like soil, climate, irrigation, pests and diseases, scion cultivar characteristics and wine goal have to be considered. Soil surveys are an essential step to collect this information and thereby identify the most important limitations that will influence decision-making. The rootstock characteristics (Table 1, compiled by the late Prof Eben Archer) of nine rootstocks in the wine industry will be discussed in this article. SO4, 140 Ruggeri and 1103 Paulsen are not so popular in the industry anymore for various reasons, but will also be discussed. The following factors must be taken into account when choosing rootstocks:
Scion cultivar and wine goal
The vigour and affinity of the scion must be considered in the rootstock choice. Scion vigour can be managed up- or downwards with the correct rootstock choice. If higher-quality grapes are required on fertile soils, a rootstock with more moderate vigour like 110 Richter or 101-14 Mgt will be recommended.
Soil potential
Soil potential is determined during soil mapping by considering the physical properties of the soil influencing root growth. Higher soil potential results in a larger root system which in turn mostly creates a larger, denser canopy if all the other environmental factors are also optimal. Rootstocks with a lower vigour can be used on soils with a higher soil potential to balance canopy growth and yield. Rootstocks with a stronger vigour can be used on soils with a lower soil potential to ensure sufficient canopy growth and yield. In this way soil potential can be managed to achieve the optimal canopy density for the chosen wine goal.
Soil-chemical properties
The presence of free lime and/or high levels of brackish salts like sodium chloride must be taken into account. Free lime in the subsoil must not be brought to the surface during soil preparation, as this action can aggravate iron chlorosis and other micro-element deficiencies. Brackish salts can be removed from the soil to some degree with gypsum applications, good irrigation water and subsoil drainage, but a salinity-tolerant rootstock like Ramsey will always be a priority on saline soils.
Signs of wetness
Rootstocks’ tolerance of wetness in the subsoil varies drastically. Not all soils are suited to subsoil drainage (mostly due to a shallow, impenetrable clay layer). In such instances rootstocks that can handle the wetness better must be chosen. If possible, soils with good natural drainage and drainable soils should always be the first choice.
Availability and quality of irrigation water
Water availability and quality is a growing problem in South Africa and a significant amount of research is currently being done on rootstocks that are highly drought and salinity resistant. Drought-resistant rootstocks are becoming increasingly popular as the availability of water decreases over time. Poor-quality irrigation water can lead to salinisation of the soil and then preference will be given to rootstocks that can handle the saline conditions.
Pests and diseases
Fresh soil samples with living roots can be tested for the presence of nematodes, phylloxera, Phytophthora, crown gall etc. If any of the pests or diseases are present, it will influence the rootstock choice and certain control measures. Irrigation water must also be tested, as it can spread bacteria, fungi, insects and nematodes. Treatment of irrigation water with filtration, chemical treatments, UV light, ozone and biological control with help with this.
Logistical problems
Ripening of large amounts of grapes at the same time can cause bottlenecks at cellars. To counteract this problem, the same cultivar can be grafted onto different rootstocks with varying vigour and phenology to distribute ripening more evenly. Rootstocks with stronger vigour, good fertility and late phenology can for example be used to delay ripening, while rootstocks with moderate vigour, low fertility and early phenology can accelerate ripening.
TABLE 1. Rootstocks sorted in descending order in terms of their tolerance to soil properties, pests and diseases.
Here are a few examples where soil and wine goal should be considered in the choice of rootstock:
High yields on deep sandy, rocky alluvial or saline soils under irrigation
Ramsey is the preferred rootstock for these soils due to its exceptionally strong vigour and salinity tolerance. The vigorously growing, dense root system of Ramsey utilises the largest volume of soil possible for water and nutrient uptake. The large root system results in strong canopy growth and higher yields. Ramsey offers good resistance against root pests and diseases like Phytophthora, phylloxera and root-knot nematode, but weak resistance against crown gall. The strong induced canopy growth (which consumes a lot of water) and the fact that Ramsey is mostly planted on sandy soils (with low water-retention ability), mean that irrigation and drainage (if necessary, especially with salinity) are essential for most vineyards on Ramsey. According to Archer, Ramsey is good to poor on lime soils.
Low yields on shallow, wet and saline duplex soils under irrigation
101-14 Mgt is well-adapted to shallow duplex soils due to its naturally shallow root system. This moderately vigorous rootstock (which is very popular for top-quality wine production) handles periods of low water tables very well and also offers good resistance against salinity. If higher yields are desired on these types of soils, a strong-growing rootstock like 8-7 USVIT will be a better choice. The last-mentioned rootstock is also more resistant against Phytophthora cinnamomi than 101-14 Mgt.
Lime-rich soils
140 Ruggeri is theoretically the champion on dry, saline lime-rich soils. Poor propagation and grafting problems at nurseries have resulted in the rootstock losing much of its popularity in South Africa. It was found that the Richters, especially 99 Richter, performed just as well on lime soils, provided that the soils are not saline or poorly drained.
The other option, especially where wetness occurs in the subsoil (without the danger of salinity) is 1103 Paulsen. This rootstock’s vigour is between that of 99 Richter and 110 Richter. 1103 Paulsen offers poor resistance against Phytophthora (just like 99 Richter), which has caused its popularity to wane in South Africa.
Red, well-drained soils
The Richters (99 and 110) are well adapted to these soils. 99 Richter is better for high yields under irrigation, while 110 Richter is more suited to slightly lower yields and instances where irrigation water can pose a problem. The Richters do not perform well with subsoil wetness or on saline soils, but offer good drought resistance.
99 Richter is very sensitive to Phytophthora which occurs naturally in soils under fynbos and pine trees.
If the soil potential is very high, in combination with strong-growing cultivars like Cabernet Sauvignon or Shiraz, a rootstock like 101-14 Mgt can be chosen to keep vigour in check for a higher-quality wine goal.
Lower-potential, wet and poorly-drained soils under natural fynbos
8-7 USVIT with an exceptional to very strong vigour, good wetness resistance and very good resistance against Phytophthora is ideal for this type of soil, especially in cooler areas where higher yields and early ripening are desired.
143 B, which is not so widely available in the wine industry anymore, will also perform well on these soils. This rootstock has a very low resistance against phylloxera. It is mostly used on the silt-rich river soils of the Orange River for raisins under flood irrigation.
Conclusion
A great number of variables must be considered in the choice of rootstocks and it is important that the soil scientist, viticulturist and winemaker consult on this decision together. In light of the strong environmental influence on rootstock performance and continuous change in market requirements, rootstock characteristics (as seen in Table 1), should be reviewed and updated regularly as new information becomes available. Rootstock choice will play a crucial role in the future to buffer vineyards against the impact of climate change. Rootstock research, and in particular new breeding programmes to establish new rootstock options, should enjoy priority.
For more information, contact Heinrich Schloms at heinrich@vinpro.co.za.
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