Efforts to exploit new technologies to breed a proudly South African cultivar which is both sustainable and adapted to our climate are currently underway.
In 1920 Abraham Perold crossed Pinot noir with Hermitage (Cinsaut) leading to what has become internationally recognised as South Africa’s homegrown wine cultivar, Pinotage. While it is not entirely certain as to why he selected these two cultivars (he left no notes regarding his experiment), it is thought that he wanted to create a cultivar which would produce wine with the drinking quality of Pinot noir, yet possess the relatively easy-to-cultivate qualities of Cinsaut.
Despite the importance of Pinotage as a symbol of South African wine, and the fact that it is the third most-planted red wine cultivar in South Africa, accounting for 16% of red wine plantings, there have been limited attempts to breed novel South African wine cultivars since Perold’s efforts a century ago. There are several reasons for this, most notably that the likelihood of creating a successful new cultivar remains extremely low. Pinotage can be seen as somewhat of fluke, only four seedlings were raised from Perold’s cross, and the one that performed the best selected, propagated, and named Pinotage.
By comparison modern day breeding programs raise thousands upon thousands of seedlings from hundreds of crosses. Selected vines are then used in subsequent crosses, and backcrosses, resulting in numerous generations before breeders obtain the desired outcome. A far cry from the romantic idea conjured when considering Perold’s intuition driven cross.
A major aim of the last fifty years of international grapevine breeding has involved the incorporation of mildew (and other pathogen) resistant traits from wild Vitis relatives into premium vinifera cultivars. Progeny raised from these first-generation crosses seldom produce high quality wines, but with time breeders have backcrossed promising material and have steadily incorporated more and more premium vinifera qualities into resistant material. However, the pathogens are not so easily defeated, and quite quickly mildew strains evolved to overcome the newly added resistance. Scientists realised that to prevent pathogen evolution, it was necessary to incorporate several genetic elements simultaneously into a single plant. This approach was made possible due to several advancements in grapevine genetics over the past thirty years, and in particular the sequencing of the grapevine genome. Plant scientists first identified genetic elements in wild cultivars that gave resistance against pathogens, and then designed so-called DNA markers which can track the presence of the DNA linked to the desirable trait, such as mildew resistance.
Breeders then use this knowledge and make directed crosses, incorporating the genetic elements in subsequent generations. By using DNA markers, breeders confirm the presence of the resistance gene at an early stage, greatly accelerating and streamlining the breeding process. These DNA marker tests can be carried out in hours, and on newly-germinated grapevine seedlings. Thus, by employing this technology, known as marker-assisted breeding, breeders have successfully been able to add DNA from multiple wild species into new “resistant” cultivars, in a process known as gene pyramiding (Figure 1).
FIGURE 1. Illustration of the multiple generations required when breeding novel cultivars to contain multiple resistance genes. Molecular tests can be used to determine the incorporation of the resistance genes (marker-assisted selection), but each generation can take up to seven years resulting in over 20 years between making the first cross and creating a wine from the final premium resistant cultivar.
In Europe and the USA the first of these novel cultivars have been released to growers and wine is being produced and sold. One of the biggest perceived obstacles in getting these new wines to market has been the pervasive idea that consumers would not be willing to give new cultivars a chance. However, research from France has found that while consumers initially had difficulty accepting wine made from these novel cultivars, these perceptions changed after having the wine’s origins described. After being informed about the reduced environmental impact and health benefits of the resistant wines, consumers in fact scored these novel cultivars higher than traditional cultivars in a general quality assessment. This speaks volumes for the impact the origin story has on the perception of wines, and on the consumer’s interest to minimise their environmental footprint and maintain a healthy lifestyle. Clearly well thought out marketing strategies are going to be crucial in the promotion of novel wine cultivars.
Currently it is foreseen that these resistant cultivars will for the most part be used in blends and will seldom be sold as single varietals. The primary reason for this is that often the typical quality traits of these cultivars are somewhat lower than that of traditional cultivars. This, together with the time-consuming nature of breeding, are the two major obstacles scientists are focusing their energies on to breed varieties that can stand on their own as premium resistant cultivars.
As DNA markers were discovered and used to track and incorporate resistance traits, similar work is now being performed for quality traits. DNA markers for berry size and colour, seedlessness, anthocyanin and aroma formation have already been developed. Breeders can now choose to incorporate (or not) the genetic elements responsible for the classic Muscat aroma derived from monoterpenes, or the peppery aroma of Shiraz, in their novel cultivar. Much work remains to be completed in this sphere as currently only a handful of markers exist. However, as scientists discover and develop more and more DNA markers for quality traits, we will move toward a situation whereby a breeder can select from a library of thousands of traits, and provided they have the germplasm at their disposal can plan a breeding strategy that will result in a spectrum of not only resistance traits, but also quality traits being targeted for inclusion in the final cultivars.
While advances in this field are being made every day, the issue of time remains. Regardless of the amount of genetic knowledge scientists generate, it will still take time to work through the cycles of breeding to get to the desired outcome. Indeed, the more traits one wishes to include, the more breeding cycles are likely to be required. One exciting shortcut that has been developed that may accelerate this process is the “microvine” (Figure 2). Instead of the usual five to six years it may take for regular grapevine to produce fruit, the microvine produces its first fruits five to six months after the planting of seedlings. By incorporating microvine into their breeding programs, breeders are therefore able to dramatically speed up the breeding process: up to 10 generations can now be grown in the time it would usually have taken to grow one. Currently microvine only exists in the Pinot noir background, meaning that all crosses made with this system will be crosses with Pinot noir. Research aimed towards generating microvine in other cultivar backgrounds would dramatically increase the scope of this tool.
FIGURE 2. Photograph of the microvine, showing berries at multiple stages of development. The microvine does not develop tendrils, and instead forms bunches as early as five months after seedlings are planted. (Image courtesy of Laurent Torregrosa of Institut Agro Montpellier, France.)
Armed with these new technologies breeders are far better positioned to meet the ever-growing consumer demand for more sustainable agriculture, while still maintaining a high quality product. We may be some way from the romanticism of the Perold approach, but we have more than made up for that with the scientific advancements of the last 30 years. South African researchers and breeders are now in a position to build on the ongoing international efforts and knowledge and create the next Pinotage: a proudly South African cultivar with strong environmental sustainability credentials and adapted to local climate and conditions.
Over the preceding two decades wine grape breeding efforts have been increasing dramatically worldwide. Driven by an ever-increasing demand for more sustainable agriculture, breeders have focused on developing cultivars resistant to mildew, thereby reducing the need for fungicide treatments. These cultivars have started to enter international markets, where consumer interest is strong. While efforts in South Africa over the same period have not been as productive, we are now well positioned to make use of new technologies and knowledge to breed our own locally relevant cultivars. The sequencing of the grapevine genome, together with marker-assisted selection technology, already allows for a streamlined approach to breeding. As more and more genetic markers are developed, breeders will be able to incorporate an increasing range of traits of interest in a targeted fashion into novel cultivars. While time remains a major obstacle to grapevine breeding, the microvine cultivar provides an exciting solution. This cultivar produces fruit as early as five months after planting of seedlings, dramatically reducing generation times, the key bottleneck in breeding programs.
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- Fuentes Espinoza, A., Hubert, A., Raineau, Y., Franc, C. & Giraud-Héraud, É., 2018. Resistant grape varieties and market acceptance: An evaluation based on experimental economics, OENO One 52(3).
- Chaïb, J., Torregrosa, L., Mackenzie, D., Corena, P., Bouquet, A. & Thomas, M.R., 2010. The grape microvine – a model system for rapid forward and reverse genetics of grapevines, The Plant Journal 62(6), 1083 – 1092.
– For more information, contact Justin Lashbrooke at firstname.lastname@example.org.