CSIRO rootstock breeding efforts funded by Wine Australia are continuing to develop next generation rootstocks with durable resistance to phylloxera and root knot nematode. In the article below, key researchers, Harley M. Smith1, Catherine W. Clarke2 and Peter R Clingeffer1 describe the science behind the work.
Susceptibility of Vitis vinifera (own-rooted) vines to grape phylloxera
Grape phylloxera (Daktulosphaira vitifoliae Fitch), an insect native to North America, is the major biosecurity risk to Australian viticulture, as varieties of Vitis vinifera (the European grapevine) used in wine, table and dried grape production are highly susceptible to this pest. The spread of grape phylloxera to major viticulture regions of the world from the mid to late 1800s devastated many of these wine grape industries. Since the discovery of phylloxera at Geelong in 1877 and later at other grape growing regions of Victoria and New South Wales, phylloxera infested quarantine zones were established to prevent the further spread of this pest. However, vineyards established on own roots throughout Australia, are highly vulnerable to the spread of grape phylloxera.
Grape phylloxera that feed on roots are the most destructive form to viticulture, as the root swellings or galls, which develop in response to insect feeding, alter root architecture and function. The formation of numerous feeding sites on roots diverts nutrients and resources away from the shoots causing a significant reduction in canopy growth and yield. In Vitis vinifera, galls produced on lignified roots develop cracks, which allow soil pathogens to enter the root resulting in cell necrosis and eventually vine death. Grafting Vitis vinifera varieties onto resistant and tolerant rootstocks is the most effective management tool to overcome phylloxera infestation. As rootstocks are designed to increase vineyard performance, most commercial rootstocks were developed in Europe and the United States over 100 years ago and lack key traits for optimal performance under Australia conditions. Moreover, these rootstocks are vulnerable to phylloxera resistance breakdown due to the low degree of genetic diversity.
CSIRO rootstock breeding history
In the 1960s, CSIRO began importing diverse sets of Vitis species and hybrids (produced from the crossing of two or more Vitis species) from the United States in order to establish a rootstock-breeding program. By the 1980s, the Australian wine industry recognised that the adoption of high vigour rootstocks, including Ramsey, in hot climate regions reduced red wine quality and colour development due to high wine pH resulting from increased potassium uptake in the fruit. To address this industry problem, CSIRO breeding activities at the time focused on the development of rootstocks with reduced vigour and potassium uptake. In 2005, three rootstocks with low to medium vigour were released by CSIRO. All three rootstocks have reduced potassium uptake and produce wines with enhanced colour and flavor attributes. These rootstocks also provide high tolerance to G4 and G30 grape phylloxera strains (Korosi et al., 2011).
As water availability and quality are predicted to decline in a warming climate, CSIRO has developed new ‘near to release’ rootstocks with improved water use efficiency and tolerance to saline soil conditions. These ‘near to release’ rootstocks are being evaluated in field trials in hot and cool climates, as well as regions with saline soils. In addition, phylloxera resistance has been assessed in these rootstocks.
Breeding for long term phylloxera resistance
The most effective vineyard management tool for grape phylloxera is to utilise resistant rootstocks. The use of grafted vines onto rootstocks in vineyard establishment is costly; therefore, it is critical that grape industries have access to a diverse set of rootstocks that provide long-term resistance to grape phylloxera.
Durable resistance is achieved by combining two or more grape phylloxera resistance traits into a single rootstock. Traditional breeding is limited in that all resistant vines having one or more resistance traits will have the same immune response and physical appearance. While inheritance studies can be performed to estimate the number of resistance traits in a rootstock, this approach is time consuming and costly. A rapid and cost effective approach to breed for durable resistance is to utilise DNA markers linked to a trait of interest (i.e. resistance trait). This requires the genetic mapping and identification of DNA markers linked to the trait. Once identified, the DNA markers are used to rapidly and effectively follow the trait during the breeding process. The ability of DNA markers to predict the trait avoids laborious and time consuming screening procedures. Therefore, thousands of plants are screened with the DNA markers using a quick molecular biology assay during the seedling development. As DNA markers are specific for each trait, this allows breeders to combine two or more traits into a plant.
‘Next Generation DNA-sequencing’ provides a cost-effective and rapid method to identify large numbers of DNA markers required for genetic mapping and DNA marker development. CSIRO’s Rootstock Breeding Team, which is funded by Wine Australia, is now using Next Generation DNA-Sequencing technology combined with genetic mapping to identify DNA markers linked to phylloxera and root knot nematode resistance traits. To this end, the CSIRO Rootstock Breeding Team in collaboration with Agriculture Victoria recently identified DNA markers linked to a new phylloxera resistance trait called RDV2 in Vitis cinerea C2-50 (Smith et al., 2018).
To read more, refer to the BMC Plant Biology published peer reviewed article, ‘Genetic identification of SNP markers linked to a new grape phylloxera resistant locus in Vitis cinerea for marker-assisted selection’. As the first phylloxera resistance trait called RDV1 was genetically mapped in Börner rootstock (Zhang et al., 2009), CSIRO researchers are utilising DNA markers linked to RDV1 and RDV2 to combine these traits for developing durable phylloxera resistant rootstocks.
[1] CSIRO Agriculture and Food, Glen Osmond, SA[2] Agriculture Victoria, Biosciences Research Division, Rutherglen, VIC
References
1. Forneck, A, Powell, KS and Walker, MA. (2016) Scientific Opinion: Improving the Definition of Grape Phylloxera Biotypes and Standardizing Biotype Screening Protocols. American Journal of Enology and Viticulture. 67, 371-376.
2. Korosi GA, Powell KS, Clingeleffer PR, Smith BP, Walker RR, Wood J. (2011). New hybrid rootstock resistance screening for phylloxera under laboratory conditions. Acta Horticulturae. 904, 53-58.
3. Smith HM, Clarke CW, Smith BP, Carmody BM, Thomas MR, Clingeleffer PR, Powell KP. (2018) Genetic identification of SNP markers linked to a new grape phylloxera resistant locus in Vitis cinerea for marker-assisted selection. BMC Plant Biology 18, 360.
4. Zhang JK, Hausmann L,
Eibach R, Welter LJ, Topfer R, Zyprian EM. (2009) A framework map from
grapevine V3125 (Vitis vinifera
‘Schiava grossa’ x ‘Riesling’) x rootstock cultivar ‘Borner’ (Vitis riparia x Vitis cinerea) to localize genetic determinants of phylloxera root
resistance. Theoretical and Applied Genetics 119, 1039–1051.