Field trial evaluation has identified three new rootstocks that maintain productivity in replant situations and produce fruit with acceptable fruit composition and are resistant to selected root knot nematode and phylloxera isolates. The efficacy of early rootstock screening techniques was demonstrated for traits including plant growth, conductance, leaf temperature and potassium measured in the nursery. As a first step for developing durable, resistant rootstocks, CSIRO has mapped new root knot nematode and phylloxera resistance loci in V. cinerea and identified molecular markers linked to these traits. Vigour, conferred by rootstocks, was stable across sites and is under strong genetic control. Trials with advanced rootstock selections have been established in collaboration with industry in different regions with a range of varieties.
Currently, the wine industry is reliant on rootstocks bred and selected overseas for conditions that may not be the same as those in Australia. Breeding and selecting new locally adapted rootstocks offers the potential to have a positive impact on vine performance and wine quality while addressing the issues of sustainability and risk management.
A major component of this project was the evaluation of existing trials planted with advanced CSIRO rootstock selections. Three new rootstock selections (C114, C113 and C20) have been identified for release and adoption by industry. These new rootstocks maintain productivity in replant situations in hot climates, have performed well when irrigated with moderately saline water in Padthaway and are resistant to selected root knot nematode and phylloxera isolates. They produce fruit with acceptable fruit composition. It should be noted that 140 Ruggeri and 1103 Paulsen performed poorly in the hot climate replant situation. Furthermore, a number of rootstocks, still under evaluation, which maintain productivity under deficit irrigation and when irrigated with moderately saline water in Padthaway show potential. Other trials, still under evaluation, involve the salt tolerant C7 selection grafted with Pinot Gris and Shiraz at Padthaway. Except for its chloride exclusion capability, the growth and fruit composition of C7 has closely mimicked that of own roots, compared to 140 Ruggeri or Ramsey.
Significant rootstock x scion interactions and rootstock x region interactions have been found from field trials with Chardonnay, Cabernet Sauvignon and Shiraz in a hot climate and Shiraz in Padthaway. This indicates that a suite of rootstocks is required to meet industry requirements and that no single rootstock will be suited to all varieties and regions. The establishment of trials with advanced rootstock selections, in collaboration with regional groups and interested growers has been undertaken to extend industry engagement and provide further information on adaptability to region and specific varietal information to enhance knowledge and foster adoption.
To test the efficacy of previous screening procedures, vine growth characteristics, fruit composition and the mineral status of grafted vines under evaluation has been linked to traits measured in previous studies. Useful traits were trunk diameter, root architecture (i.e. root type, diameter, number and angle) and measurements in the nursery plants under well-watered and deficit conditions of growth traits (shoot length, pruning weight), physiological traits (conductance, leaf temperature and transpiration efficiency) and leaf mineral elements, in particular potassium (K).
While the three new selections possess resistance to certain root knot nematode species and phylloxera genotypes, there is a pressing need to develop rootstocks with more durable resistance to a broad-spectrum of root knot nematode and phylloxera genotypes. As a first step in achieving this aim we have identified new sources of resistance and developed molecular markers that will ultimately be used to combine these new resistance traits with existing resistance loci in new rootstock breeding lines. In this project, we successfully mapped the Vitis cinerea C2-50 root knot nematode resistance locus, MJR1, which provides complete resistance to two major species of root knot nematode in Australia, Meloidogyne javanica and M. arenaria. The V. cinerea C2-50 phylloxera resistant locus, RDV2, was also mapped and molecular markers were identified. The RDV2 locus provides good resistance to the two major phylloxera genotypes in Australia: G1 and G4.
The project has demonstrated large impacts of rootstock genotype on vine growth characteristics which have been linked to fruit and wine composition. In particular, strong genetic control of conferred vigour (pruning weight) by rootstock genotype was stable across different environments. In general, it was associated with negative effects on fruit composition (high pH, malate and K and in some instances with reduced berry anthocyanins and wine colour). With the exception of malate, which was closely linked to pruning weight, all other growth and fruit composition parameters were more impacted by environmental conditions rather than by rootstock. The project has also demonstrated that rootstocks with large berries and large bunches generally had poor fruit composition.
Over the course of the project there has been significant interaction with industry with presentations to industry groups, wine companies and growers, supported by tasting of wines produced from new rootstock selections. Mother vine plantings of new selections have been established to ensure that adoption is not limited by the supply of propagation material.