Evaluating and demonstrating new disease resistant varieties for warm irrigated regions
Abstract
The project established an experimental vineyard for the evaluation of the first generation of Australian mildew resistant vines in a warm irrigated wine region. A larger scale trial planting of 20 white selections was undertaken in the Riverina (NSW) during the 2013/14 growing season. Detailed field evaluations at the NWGIC experimental vineyard were conducted over three seasons, and experimental winemaking and evaluations were undertaken in the last year of the project (2016/17). Red selections were established at the NSW site from late 2015 for evaluation. No mildews were observed on the unsprayed vines during the term of the project and sensory evaluation of the white wine identified aromatic wines.
Summary
Breeding new grapevine cultivars with high resistance to fungal pathogens presents an opportunity to substantially reduce the use of plant protection agents, and therefore lower production costs and reduce the impact of viticulture on the environment. Resistance can be achieved by crossing suitable parent cultivars, screening for desired disease resistance and other beneficial traits, and then evaluation of superior selections and their winemaking potential under field conditions for several years before release.
As part of a previous project supported by Wine Australia (CSP 0904), 1200 new selections from the CSIRO breeding program which showed strong resistance to powdery mildew and reduced susceptibility to downy mildew were evaluated under field conditions. Based on disease resistance and other physiological traits, 20 white selections with a range of potential wine quality attributes were identified. These vines represent the first generation of mildew resistant vines produced using marker-assisted selection in Australia. The first larger scale trial planting of these selections in NSW was undertaken in the experimental vineyard of the National Wine and Grape Industry Centre (NWGIC) in cooperation with McWilliam’s Wines in the Riverina during the 2013/14 growing season. This initial planting consisted of 20 white selections that had demonstrated superior plant performance at the Barossa site and produced diverse wine flavours identified as of interest by commercial winemakers during sensory evaluation. Red selections required further evaluation at the Barossa site at that time and consequentially were planted in the 2015/16 season adjacent to the white selections. Both selections were trained and managed similarly and the red selections now have an established trunk and cordon after the second season.
After the first season of sprawling of the white selections (2013/14), in winter all vines were pruned to three buds and pruning weights were assessed, these varied considerably by three-fold. In the second season (2014/15), two shoots were left to grow from these buds to mid-spring, and then the best shoot was selected for the trunk and was cut just above the cordon wire. The total shoot length was measured prior to these changes, with the growth between selections varying by about 30%. From the two upper buds and/or laterals the bilateral cordon developed, all vines had reached the appropriate cordon length or more by the end of second season. The training included disbudding, fixing the trunk on stakes and the shoots for the cordon on the wires. The vines were sprayed against mites in spring with wettable sulfur and received fertiliser applications. Weed control was conducted during the season with herbicide sprays in the vine row and the mid row, and frequent mowing occurred. At the end of the first season, the pruning weights were determined and showed four-fold differences between the 20 white and red selections.
In the third growing season (2015/16) the same vineyard management program was undertaken in relation to weed and mite control, but fertiliser application was increased. The longer shoots that were hanging into the rows were shortened in late spring. Basic berry and juice parameters were determined at harvest together with yield and yield components, with the bunch and berry size showing visual variation, being more than two-fold between selections. Berry ripeness was 10 Brix apart in mid-February, consequentially juice pH and TA varied as well with about half a pH unit and 3 g/L for TA. There were also considerable differences between the white selections for yield and pruning weights taken in winter showing more than two- and four-fold differences respectively. The project background and initial results were presented in talks in the Orange wine region and the Hunter Valley, a seminar and field day was held at the NWGIC in spring 2016.
In the last season (2016/17), the performance of the white selections was further evaluated, there was no sign of mildew in these or the red selections, despite appearance of powdery in the Merlot vines that were located in the adjacent block. However, some damage to the berries and bunches was observed due to heat and sun exposure in mid-summer, but the canopies were still not fully developed due to the vine age. The white selections showed three-fold differences between yields with a harvest time over six weeks due to variation in maturation between these selections. From the middle of February to early April, grapes (about 100 kg) were harvested at suitable berry ripeness (around 22 Brix) from each selection and used for the winemaking, but five selections did not reach a suitable level by early April.
Two wines were made from each of the 20 selections and these were assessed two months after bottling in the Riverina at McWilliam’s Wines for sensory attributes. This included the ranking of aromas; tropical, citrus, stone fruit and floral as well as attributes for mouth acidity, length of flavour and bitterness. This preliminary assessment of wines showed a considerable difference in the overall scores and preferences. These differences were particularly pronounced in floral aroma and the acidity attribute. The assessment and other information will be published in an industry journal later. These white and red disease resistant selections will be further assessed over the next few growing seasons to ensure a meaningful evaluation of vine performance and wine characteristics.
Regional field trials to evaluate plant performance and wine quality is an important activity to determine the best selections for different regional climates, different management systems and to also engage local viticulturists and winemakers in the assessment of wine made from grapes produced in the different regions. It is recommended that four regional field sites be established for long-term assessment of these new disease resistant selections and future scion and rootstock selections. The four regional field sites would cover the main climates (cool to hot irrigated) where grapes are grown and the major grape growing regions of Australia. It is recommended that sites be established in the Barossa Valley SA, Irymple VIC, Riverina NSW, and Orange NSW. The sites would be managed by CSIRO or State Departments to ensure health of the plants and the collection of research quality data.
It is expected that regional field trials will be an effective pathway to adoption mechanism to help drive industry adoption and uptake of new grapevine selections. The regional sites would also act as mother block plantings for the Australian industry from which healthy cuttings could be sourced.