New rootstock research: the salt and irrigation benefits
New research by the CSIRO has confirmed the potential of rootstocks to reduce the impact of salty soil or irrigation water – a problem likely to become even more widespread in viticulture as climate change brings longer, hotter and drier summers.
Extensive trials in the southeast of South Australia highlighted a relatively wide range in salt tolerance capacity across eight commercially available rootstocks and led to the creation of a Salt Tolerance Index (STI) for ranking available rootstocks. Further testing of the STI with a range of scion-rootstock combinations in a range of regions was recommended.
The research, which was funded by the GWRDC and carried out in collaboration with the AWRI, went beyond traditional field tests to include compositional and replicated sensory analysis of wine made from the grapes.
‘We had a particular interest in how much salt might have accumulated in the juice and carried through to the wine, and just what that accumulated salt did in terms of how the wine looks and tastes’, said principal investigator Dr Rob Walker, from CSIRO Plant Industry.
‘Normally tests for salinity tolerance only look at yield or amount of salt accumulated in leaves, petioles or fruit, but the reality is that you’ve got to look at a combination of factors.
‘We included a range of measured characteristics such as yield, leaf area index, grape juice chloride and sodium concentrations and wine colour density then created the index, which ranks rootstocks for salinity tolerance in a slightly different context to what has been done before’.
The research suggests a salty taste in red wine occurs when chloride levels are around 450-500 mg/L. Salty wines also have a more viscous mouth feel, but it is not clear what causes this.
The sensory data also provided valuable information about other wine attributes related to the rootstocks, such as differences in flavor intensity and colour.
The trials tested five standard rootstocks (140 Ruggeri, 1103 Paulsen, 110 Richter, Ramsey and 101-14) and three rootstocks bred during previous GWRDC-funded projects at CSIRO (Merbein 5489, Merbein 5512 and Merbein 6262). Shiraz was the scion in each case.
The capacity for chloride exclusion was similar for all except Merbein 6262, which accumulated up to 480 mg/L of chloride in wine. However, when other factors such as leaf area index, concentrations of chloride and sodium in the grape juice and wine colour density were taken into account, Merbein 5489, 110 Richter and 140 Ruggeri moved to the top of the list in terms of best salt tolerance.
Salt tolerant rootstocks appear to work by limiting chloride accumulation in leaves and fruit through lower root to shoot transport. The research on chloride exclusion, which was carried out in collaboration with the University of Adelaide, identified several candidate genes potentially involved in the chloride exclusion process.
The CSIRO has already begun two broader projects, again funded by the GWRDC. One seeks to develop new rootstocks designed specifically for Australian conditions, including trialing of advanced selections at a range of sites, and to develop molecular markers to screen for resistance to phylloxera and nematodes.
A complementary project in collaboration with the University of Adelaide seeks to better understand abiotic (water, heat and salt) stress tolerance in rootstocks, including, advancement of marker development for chloride and sodium exclusion to support rapid rootstock breeding.