In order to better understand mechanisms of plant disease resistance, cold tolerance, etc. geneticists are turning to whole gene sequence technologies such as genome-wide association studies (GWAS) and whole-genome resequencing (WGRS).These new technologies enable prediction of the effects of DNA sequence variants on gene function when a large array of crops are subjected to some of these newer methodologies. But these technologies are still very expensive.
Simple sequence repeat (SSR) analysis of grapevines:
A good starting point has been the use of microsatellite DNA fingerprinting (SSR) of plant genomes which has enjoyed a great deal of success over the last 30 years. This technology is also relatively cheap. It is particularly useful in plant genetic studies because microsatellite alleles are inherited by offspring in a co-dominant Mendelian fashion from their parents. This fact enables the determination of parent-offspring relationships among grapevines as well as finding out whether any disease-resistance genes have been likely inherited from one or other parent. This idea has become a reality because other complementary DNA technologies which target disease-resistance genes are able to associate those genes with some of the microsatellite alleles. By following the inheritance of some of those 'indicator' SSR alleles one should be able to locate the disease-resistance genes in those plants.
Old World hybrid cultivars:
A genetic evaluation of the Old World hybrid rootstock cultivars such as Jacquez and Herbemont, has been long overdue. These ancient rootstock cultivars were also successfully used to produce wine and were known as direct producer hybrids (DPH) in France during the phylloxera scourge (1870s onwards). They were found to be more disease-resistant than the European Vitis vinifera cultivars since they were unintentional offspring resulting from natural cross-hybridization between wild American Vitis aestivalis/cinerea species and (unknown) European Vitis vinifera cultivars. That pollination event is understood to have occurred in the southeastern states of America over 220 years ago.
Many Herbemont seedlings were deliberately produced in France from the early 1870s, and two of the more famous seedlings which were produced there at the time included Herbemont Touzan and Herbemont d’Aurelles (itself a Herbemont Touzan seedling) among others. Meanwhile the famous experimental viticulturist, Prof. T. V. Munson (Texas, USA) also began producing Herbemont seeds in the late 1870s. The original idea was to create American wine grape varieties that not only showed disease resistance, but that would also yield acceptable wines - especially acceptable to the European palate.
During his grape-breeding experiments T. V. Munson produced many Herbemont seedlings one of which he named Black Herbemont. However, Munson was never exactly sure which grape variety he had actually crossed/hybridized with his Herbemont to produce the Black Herbemont. It was later reported in the various horticultural catalogues at the time that Black Herbemont was a 'rare' pure Herbemont seedling, while others reported that it was the result of crossing Herbemont x Norton (Cynthiana) varieties. As expected, most of the Herbemont seedlings were less resistant to phylloxera than the true Herbemont, likely due to their somewhat higher V. vinifera genetic component, and most Herbemont seedlings were eventually discarded.
Origins of South Africa's Black and White Herbemont rootstocks: Using microsatellite DNA analysis, Nel and Rodrigues traced the origins of the Black and White Herbemont hybrid rootstock cultivars (including the Jacquez) which were originally imported into the Cape Colony in 1892. They were imported for the express purpose of grafting our European vinifera grapevines that were being threatened by the phylloxera epidemic. Phylloxera had mysteriously appeared for the first time in Mowbray in the Cape around 1886.
According to the microsatellite DNA fingerprinting analysis, it has been revealed that the Black Herbemont was derived from a crossing between a White Herbemont cultivar (an Herbemont open-pollinated seedling) and the Madeira Jacquez (the original Jacquez cultivar).
What this now tells us is that Munson did not always employ the original true Herbemont for some of his breeding experiments and satisfactorily explains why South Africa very soon had to abandon these two cultivars as rootstocks in favour of the original Jacquez. It is now common knowledge that the Jacquez cultivar went on to become South Africa’s most successful rootstock, having been deployed for almost 60 years until it was replaced by more phylloxera-resistant 100% American hybrid rootstocks in the 1960s.
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Jeronimo Rodrigues PhD (Biochemistry, UCT)(updated, September 26, 2018)