Field trials : new scion-rootstock combinations and evaluation of new technology for improved water use efficiency and reduced costs

Abstract

Four novel ‘no-spray’ scion varieties with complete mildew resistance, produced through the CSIRO breeding program, were evaluated in a multi-factorial vineyard trial with different planting density and irrigation management strategies. Two of the scion varieties combined ‘no-spray’ with a ‘no-prune’ trait, meaning that both spray and pruning costs were avoided. All of the varieties produced commercially viable yields and commercially acceptable table wine. Combining high-density planting with reduced water inputs and the cost saving from not requiring fungicide sprays and/or pruning maintained commercially viable production levels, but with higher profitability indicated.

Summary

CSIRO has bred grape varieties (non-GMO) that are ‘no spray’ with multi-genic resistance to both powdery and downy mildew. This trait has also been combined with a ‘no-prune’ growth habit to produce varieties that don’t require annual pruning in order to limit growth and stimulate fruit production. Both red and white fruited varieties have been produced from the ‘no-spray’ and combined ‘no-spray’ ‘no-prune’ traits.

A previous project, also co-funded by Wine Australia (CSA 1305), established a trial planting using this new varieties at the SARDI Nuriootpa Research Station in South Australia. This trial not only incorporates a red and white varieties of these new scions (four in total), but has them grafted to three rootstocks as well as being own-rooted. The scion: rootstock genotype combinations are grown at two planting densities (1,572 and 5,249 vines per hectare) and under two irrigation regimes.

This project monitored the trial for three seasons (2017/18 to 2019/20), with harvest collected for a fourth vintage (2021), assessing growth, production, fruit composition and winemaking suitability of the scion:roostock/management treatment combinations. The impacts of the ‘no-spray’ and ‘no-prune’ traits on fruit production costs were then determined, together with the impact of management strategies employed. Finally, the project also used the trial to examine the potential of canopy temperature to be used in irrigation management decisions as a measure of vine water status. Most the work on this latter subject was moved to another Wine Australia co-funded project (CSA1701-3.1), but results from initial testing with the ‘ArduCrop’ sensor are provided here and support the viability of using canopy temperature to estimate vine water status.

Crucially, the project results demonstrated that all four new varieties (‘no-spray’ red, ‘no-spray’ white, ‘no-spray’+‘no-prune’ red and ‘no-spray’+‘no-prune’ white) were suitable for table wine production under the various management treatments and irrespective of rootstock, with both micro-ferments and small-lot winemaking producing wines with acceptable ethanol, pH, acid, colour and phenolics. The ‘no-prune’ red had a longer fruit maturation requirement at the natural crop load to reach a total soluble solid concentration of 22°Brix, but was typically able to achieve this where there were no other problems (extreme weather, COVID-19 restrictions on vineyard access). Importantly, no mildew infection was observed on any of the vines during the three seasons of work, despite no fungicide sprays at any time.

Harvest yield was also commercially acceptable, with the two ‘no-spray’ only scions averaging 12.3 and 11.1 t ha/Ha under standard management conditions for the red and white varieties respectively. Production with reduced irrigation was reduced by approximately 20% in both, but slightly more than doubled by high-density planting. The two ‘no-spray’+’no-prune’ scions produced 13.6 and 17.7 t/Ha, despite not having filled the cordon wire by the end of the project. This was with high-density planting, but was still close to the regional production levels, even taking that into account.

Vine vigour varied between genotypes, with the red varieties having lower vigour than the white varieties and the two ‘no-prune’ genotypes, not surprisingly, having lower vigour than the ‘no-spray’ only genotypes, which had a typical ‘wild-type’ (WT) vinifera growth habit. In fact, by the end of the project (six years after planting) the ‘no-prune’ genotypes’ had yet to completely fill the cordon wire. For the WT vines vigour was greater at high-density planting than at standard-density and, surprisingly, was not only unaffected by reduced irrigation in the standard-density treatment, but actually higher with reduced-irrigation than standard irrigation at high-density. It is possible that this was due to carry-over from higher irrigation rates in the high-density plot during vineyard establishment. Soil moisture and canopy temperature data both indicated that the reduced-irrigation treatments did indeed have less water available to the vines during the course of this project.

The ‘no-prune’ varieties suffered significant damage from climate extremes early in the project and were protected with shade netting. However, by the end of the project this was not required.

Rootstock genotype affected both vigour and yield to some extent, with known low and high conferred vigour rootstocks having the expected influence on the ‘no-spray’ WT scion genotypes. For the ‘no-prune’ varieties, grafting somewhat reduced production with own-rooted vines performing better.

The cost of production analysis was limited in detail and had to make assumptions about potential fruit value as the varieties are unreleased, but indicated that all the varieties should be able to be grown profitably and that the red ‘no-spray’ WT variety in particular would likely be more profitable grown at high-density, than at standard-density planting.

In summary, the results of the project indicate that all the scion varieties could produce commercially viable quantities of fruit and make acceptable table wines. Further, that combining high-density planting and reduced irrigation (per unit length row) has the potential to improve vineyard profitability.