The Art and Science of Grape Variety Identification
Ampelology, Not Ampelography
The first time I met one of the world's most famous wine experts, now many years ago, it took me all of two minutes to say something wrong. Jean-Claude Berrouet, for over forty years the head of winemaking at J. P. Moueix (the venerable French négociant firm that produces and sells legendary wines such as Petrus, Trotanoy, Magdelaine, and California's Dominus), stopped in mid-conversation, smiled, and pointed out I had used an incorrect term. That pernicious term was ampelography.
Ampelography is the science of vine description and classification based on observation and pictorial illustration of grapevines-and strictly speaking, nothing more. The term derives from the Greek ampelos (grape) and grapho (write) and literally means "vine description" or "writing about grapes." Historically, vine varieties and grapes have always been described and carefully reported via beautiful drawings, and later, photographs. Today, everyone uses the term ampelography to refer to the study of grape varieties in the broadest sense, including genetic studies, but such a broad use is a mistake. That fateful day now decades ago, I made that mistake, and Berrouet let me know it. I haven't stopped learning from the man since.
The fact is that modern grape scientists can count on so much more than their powers of observation in their search to identify grape varieties-and it's a good thing too, as we shall see. Modern advances in cellular and molecular biology have made it easier today to correctly identify grape varieties. Whereas grape cultivar characterization had been traditionally carried out using morphological and phenological observations, nowadays DNA analysis techniques based on molecular markers, when correctly performed, are able to provide objective information on the identity of a species. These techniques can also help clarify the origins of grapevine cultivars. Since grape identification no longer involves just the art of observation and graphic reproduction, but many other branches of science too, the correct name for grapevine science ought to be ampelology, not ampelography. Others besides Berrouet agree, yet wine writers and university experts have continued to use the older term out of habit. By analogy, consider whether, should you have a stomach problem or break an arm, you would prefer to go to a gastroenterology or orthopedic clinic, or to a gastoenterography (whatever that may be) or orthography clinic. In the latter they might teach you to write better, but it might prove hard to do with a broken arm.
"People can't speak to each other if they don't know if they're talking about the same grape variety," says Carole Meredith, a viticulturist and plant geneticist at the University of California at Davis in California, to whom we are all indebted for the great advances made in the past twenty years in identifying grape varieties accurately (Meredith 2002). Stella Grando, a professor at the Research and Innovation Center of the Applied Molecular Laboratory at the Fondazione Mach of the Istituto San Michele all'Adige, one of Italy's greatest (and nicest) grapevine scientists, told me that she feels exactly the same way: "A variety-oriented enology, aiming to obtain a distinct wine from a specific cultivar, requires complete knowledge of the cultivar itself.";.
History of Ampelography in Italy and Europe
Before modern biomolecular techniques became available, all we had to describe grape varieties was ampelography. The ancient Romans made the first attempts at classifying grape varieties in an orderly fashion. The simplest classification divided grape varieties into two broad categories, table grapes (e.g., ad mensam, ad cibariae, ad suburbanae) and wine grapes (e.g., ad bibendum, ad vindemias), and then by descriptors such as berry color and grapevine phenological characteristics. .
The first true ampelographers were born in the nineteenth century. In Italy, Acerbi and Gallesio were the most famous, but there were other experts, such as Ciro Pollini, whose treatise in 1822 on the vines and grapes of the Verona province alone described eighty-two different grape varieties (fifty-five red and twenty-seven white). While France's Count Odart published various editions of his Ampelographie Universelle (1849, 1874), Italy saw the creation of its first varietal collections, and experts such as Mendola (1868), Incisa (1869), and Di Rovasenda (1877) described accessions with ever greater accuracy. In 1872, the first International Commission of Ampelography was convened in Vienna: it coordinated European viticultural efforts and led to a catalog listing the grape varieties of Europe. In Italy, the Comitato Centrale Ampelografico(Central Ampelographic Committee) and theCommissioni Ampelografiche Provinciali (Provincial Ampelographic Committees) were born: their mission was to study all of the nation's grape varieties, including their winemaking potential. Their work was summarized in the Bollettini Ampelografici (Ampelographic Bulletins) published mainly between 1876 to 1887 and still extremely useful today. Other countries developed varietal catalogs, containing either drawings or photographs of grapes: best known are those of France's Viala and Vermorel (1901, 1909). Italy's Molon (1906) was also among the Italian experts called upon to contribute to Viala and Vermorel's opus. In Italy, the Istituto Sperimentale per la Viticoltura di Conegliano Veneto (Research Institute for Viticulture), now called the CRA-VIT Centro Ricerche per la Viticoltura, was founded in 1923 as the Regia Stazione Sperimentale di Viticoltura ed Enologia, and has been the leader in the selection and conservation of Italy's grapevine genetic material over the years. From the beginning, grape variety collections were set up in the experimental vineyards of a farm in the town of Susegana (near Treviso). By 1967 the numbers of grape varieties grown had doubled, and since then many similar, world-class research institutions dedicated to grapevine study have been created.
Ampelology, or the Identification of Grape Varieties
Ampelology is more of a science than the art form ampelography was (and is), and it includes diverse techniques and methods by which to identify grapes. These include:
• Ampelographic descriptions and ampelometrics: the former describe the morphological characteristics of grapevines; the latter consist in measurements of organs and are less subjective than ampelographic methods.
• Biochemical methods, such as isoenzyme analysis or aromatic molecule precursor analysis, that reveal the presence or absence of specific enzymes and of some metabolites in each variety.
• Biomolecular methods, which reveal DNA sequences specific to single varieties.
The use of all three methods together allows for more accurate variety identification. Ampelographers and geneticists cannot function to their full potential working alone; in fact, the identification of grape varieties is very much a team effort.
Ampelography is the first step toward characterization of a grape variety and of fundamental importance for subsequent genetic testing. Grapevines are classified based on the appearance of their leaves, shoots, berries, bunch appearance, and color, and by viticultural parameters such as date of flowering or harvest. The data compiled is tremendously specific and precise; for example, within the category of leaves, everything from single indentations to color of the veins is considered. Another example is the shoot tip, the color of which can be a very useful descriptor in the spring: for instance, the white tip of Merlot distinguishes it from Cabernet Franc or Cabernet Sauvignon, with which it is often confused. These ampelographic characteristics are classified by qualitative, quantitative, and alternative characteristics, and may be either present or absent. By compiling this data, a reasonably accurate but not infallible identification of a variety may be made. However, difficulties abound. For one, an immense level of experience is necessary to correctly identify cultivars on the basis of physical parameters alone (and not all researchers have that experience or the time and means to acquire it), and it is very easy to make mistakes. Furthermore, grapevine morphological features such as leaves and bunches can be greatly affected by the environment. For example, the size of grape bunches and berries can differ based on water access and the availability of minerals in the soil, as well as the yields of the grapevines.
Also, morphological identification can be applied only when berries and leaves are fully visible, so ampelographic recognition can take place only at certain times of the year. The onus is then on nursery personnel to work accurately and correctly: only several years after a vineyard is planted are mistakes noticed. Everyone knows of producers who thought they were growing Cabernet Franc or Merlot or Albariño only to realize their vines were Carmenère or Savagnin instead. Nursery mistakes such as these are more frequent than is commonly believed.
To increase precision, ampelometric methods were added to ampelographic observation. Ampelometric methods possess the advantage of being less subjective than ampelographic characteristics, as they are measurable. In 1983, the Office International de la Vigne et du Vin (OIV) published the Code des caractéres descriptifs des variétés et espèces de Vitis (Code of the Descriptive Characters of the Varieties and Species of Vitis) in French, English, Spanish, and German. In it, they presented the codification of 128 ampelographic descriptive characters (later reduced to a more manageable eighty-four), a method adopted by other international organizations, including the International Board for Plant Genetic Resource (IBPGR) and the International Union for the Protection of New Varieties of Plants (UPOV).
Chemical Analysis: Isoenzymes, Secondary Metabolites
Until DNA testing became routinely available in the twenty-first century, biochemical methods were most often used to bolster ampelographic information about varieties. Life is possible because of biochemical reactions catalyzed by enzymes (proteins composed of amino acid chains), the structure of which is determined by corresponding DNA sequences. Isoenzymes are different molecular forms (in size or electric charge) of enzymes that catalyze the same reactions. Since they are correlated to multiple but specific gene loci, they behave as genetic markers. Isoenzymes can be differentiated by electrophoresis, which relies upon their different levels of mobility within a gel to which an electric current has been applied. The diverse positions reached by the different isoenzymes are called "profiles" or "patterns" and are identified by a specific number. Four enzymatic systems may be used, but two are most reliable: glucose phosphate isomerase (GPI) and phosphogluco mutase (PGM). Though useful, isoenzyme analysis has limitations (Stavrakakis and Loukas 1983; Calò, Costacurta, Paludetti, Calò, Aruselsekar, and Parfitt 1989). While grapes with different isoenzyme patterns are certainly different varieties, it is not necessarily true that those with similar patterns are the same variety. However, numerous cases of synonyms and homonyms of grape varieties have been apparently resolved with this method (Calò, Costacurta, Cancellier, and Forti 1991; Moriondo 1999).
We know grape-derived secondary metabolites are the principal source of wine aroma, flavor, color, and taste and that they include polyphenols (like anthocyanins and flavonols) as well as aromatic compounds (like monoterpens). Bate-Smith was the first to show, in 1948, the role of phenolic pigments as genetic markers, but Ribereau-Gayon was the first to apply this tool to grapevines, in 1953. Unfortunately, concentrations of these compounds can be affected by a number of variables, including climate (Jackson and Lombard 1993), water supply (Hardie and Martin 1990), leaf area to crop ratio (Iland, Gawel, Coombe, and Henschke1993), and canopy management (Smart and Robinson 1991). For example, wines made from aromatic varieties are immediately recognizable because of their spicy, floral, and very fruity aromas: these are the result of aromatic molecules such as terpens, benzenoids, and norisoprenoids. All grapes contain these molecules in varying amounts, but grapes defined as "aromatic" have more. Wines made with Moscato varieties are especially rich in a terpen called linalol, while members of the Malvasia group have always been characterized by another terpen, geraniol. The two molecules are responsible for different aroma types, which once were used to distinguish Moscato wines from aromatic Malvasia wines: while linalol leaves a sweet, musky impression typical of all the Moscatos, geraniol recalls more refined rose-like aromas, typical of all the aromatic Malvasias, white and red. For instance, Moscato Rosa's aromatic profile differs considerably from that of Moscato Bianco, and is more similar to that of Brachetto or Malvasia di Casorzo. For the same reason, Malvasia delle Lipari has an aroma profile that makes its wines more reminiscent of some Moscato varieties than of other Malvasias. Unfortunately, though the aromatic expression of grapes is genetically predetermined, growing conditions and winemaking techniques can easily alter the aromatic profiles of wines to a significant degree.
Cellular and Molecular Biology Techniques
The genetic patrimony of each individual is mainly constituted by DNA (deoxyribonucleic acid) contained within the nucleus of cells, though DNA is not found just in nuclei, but also in other organelles within cells, such as mitochondria. For DNA's content to be actually useful, it needs to be copied and transported outside the nucleus to other structures called ribosomes, where its information is translated and transformed into proteins. This task is performed by two forms of RNA (ribonucleic acid): messenger RNA (mRNA) and translator RNA (tRNA). It is the mRNA that transports DNA information to the ribosomes where the tRNA then proceeds to have DNA's information translated.
Just like human beings, all grapevines have distinct DNA profiles. DNA testing was introduced by Jeffreys, Wilson, and Thein in 1985 and has been successfully used in the field of criminal law-it was first applied to vine research by Thomas and Scott in 1993. DNA testing represents the current state of the art for grape variety identification, as DNA can be obtained from every kind of plant tissue, can be carried out at any time of the year, and is not influenced by the environment. Initially, the molecular techniques used included restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), and random amplified polymorphic DNA (RAPD), but these have been largely replaced by the use of microsatellite technology, which is characterized by high reproducibility and standardization. Microsatellite markers are the most commonly used DNA test for identification of grapevine cultivars today. There are two types of microsatellites most used at present: nuclear microsatellites (or nuclear simple sequence repeats, nSSR), which are the best known and most used to date, and chloroplast microsatellites (CpSSR), which may be more useful in parentage studies.
To genetically identify a vine, we take a sample of the DNA of that vine, chemically purified from the other plant components. Specific, small segments of DNA called alleles are targeted and the polymerase chain reaction (PCR) technique is used to make millions of copies of selected marker segments. The alleles in one marker site of a given variety are compared with those present in the same marker site of another variety. Two vines are considered to belong to the same variety if they possess identical sequences of DNA in a sufficient number of these marker sites, called microsatellites and also known as single sequence repeats, or SSR. Microsatellites are simple sequence repetitions scattered randomly throughout an organism's DNA that were long believed not to be transcribed and translated; in other words, not to code for proteins. (However, as we shall see later in this chapter, it is becoming apparent that this view is increasingly obsolete.) As microsatellites are constant within each variety and differ from those of other varieties, they act as molecular fingerprints for varieties. The identification of unknown vines is done by comparing the genotype obtained from the sample with reference genotypes of cultivars stored in internationally available databases, much as with fingerprints in criminology. A variety is considered "new" if the microsatellites do not match any in the database. Depending on the number of sites studied, the probability of different varieties having the same SSR pattern by chance is roughly one in eight billion.
While several sets of SSR markers have been proposed for grape research, the best known are the set of six suggested by the grape Genetic Resources (GENRES) projects. This project established the European Vitis Database (EVDB), which now includes data for more than 28,200 accessions, representing the Vitis collections of eighteen European contributors. The research group also selected six microsatellite loci allowing for the identification of grapevine cultivars (VVS2, VVMD5, VVMD7, VVMD27, VrZag62, and VrZag79). Though most researchers believe that six loci are enough to determine genetic identity between most species, at least nine are indicated for varieties that are close genetically. Statistically, the probability identity value increases by six powers of ten when nine, rather than six, SSR loci are studied. Analyzing more than ten loci of the grapevine genome further increases the accuracy of cultivar identification: the ten microsatellite loci internationally accepted are VVS2, VVMD5, VVMD7, VVMD25, VVM27, VVMD28, VVMD31, VVMD32, VrZAG62, and VrZAG79. Recently however, researchers have begun to think that even more loci might be necessary to increase the discrimination power of investigations performed.
Recently, another molecular DNA marker has come into use: single nucleotide polymorphisms, or SNPs (pronounced "snips"). Future genetic grapevine research will likely combine both SNP and SSR assessments. Lijavetszky, Cabezas, Ibanez, Rodriguez, and Martinez-Zapater (2007) found that SNPS provide a lower probability identity than microsatellites, so higher number of markers are needed to generate similar probability values. The advantage of SNPs is they are easier to work with than SSRs.
Chloroplast microsatellite studies are of particular interest, since the genetic material of chloroplasts (small chlorophyll-containing organelles that are the photosynthetic units of plants) is transmitted from mother to daughter without undergoing any variation. As a result of its perceived conservative rate of propagation, chloroplast DNA has proven extremely useful in plant population biology studies examining the migratory routes of species, as shown by Weising and Gardner (1999) and Avise (2000). Chloroplast-specific haplotypes, or chlorotypes, have been found in indigenous germplasm believed to be typical of the specific region. For chloroplast SSR analysis, as many as nine polymorphic chloroplast microsatellite loci have been used, such as cpSSR3, cpSSR5, and cpSSR10 (Arroyo-Garcia,Ruiz-García, Bolling, Ocete, López, Arnold, et al. 2006; Imazio, Labra, Grassi, Scienza, and Failla 2006).
Hits and Misses of Ampelology
Through the combined efforts of the above methodologies, we have apparently been able to correctly identify many erroneously named cultivars. Examples include Pignoletto, which was proven identical to Grechetto di Todi(Filippetti, Intrieri, Silvestroni, and Thomas 1999), and Bonarda in Argentina, shown to be identical to Corbeau (known as Charbono in California) (Martínez, Cavagnaro, Boursiquot, and Aguero 2008). However, unless ampelographic and genetic studies are performed with utmost care, wrong attributions are common: well-known mistakes made in the past include misidentifying California Refosco as Mondeuse Noire, Cilegiolo as Aglianicone, and Casetta as Enantio. These pairs of cultivars are unrelated, and provide an example of how incorrect ampelographic identifications can nullify properly conducted genetic testing-and of course, the converse is also true. Accurately labeled vine samples in reference collections all over the world are a must, because genetic testing via microsatellite analysis can only confirm or rebuke the ampelographic identification proposed. Nowadays, some nurseries independently test new acquisitions, and offer to have the DNA of planting material of newer varieties tested at the client's cost.
This rigor is necessary. Since genetic analysis is performed on vineyard collection grapevine samples (from a university or another source) that were originally identified by an ampelographer (and how experienced an ampelographer is anybody's guess) or by the farmer who originally planted it, subsequent genetic testing is at the mercy of that original identification. If grapevine samples are misidentified and mislabeled in varietal collections, then genetic test results will be hopelessly wrong and of no use. In the California Refosco example, a mistake was easy to make since the Refoscos and Mondeuse Noire resemble each other. The university collection sample had been identified ampelographically as a "Refosco" and when it was later found that its DNA matched that of Mondeuse Noire, it was logical to conclude that Mondeuse Noire and Refosco were one and the same. However, when DNA tests were performed on authentic Refosco varieties in Italy, the DNA of which is nothing like that of Mondeuse Noire, it became apparent that the California grapevine had been misidentified ampelographically, and had in fact been Mondeuse Noire all along. This example clearly demonstrates why tested, accurate ampelographic collections are a must. What's more, to refer to a generic "Refosco" is also incorrect: since there are at least four different Refoscos known, one needs to specify clearly which Refosco is being studied, for example, Refosco del Peduncolo Rosso or Refosco Nostrano. Clearly, Mondeuse Noire could not have been identical to both of those. It's either one or the other, and as it turns out, it's neither.
DNA Profiling: Potential Problems and Pitfalls
Several studies have shown that germplasm collections harbor many homonyms and synonyms (Ibanez, Andres, Molino, and Borrego 2003; Cipriani, Spadotto, Jurman, Di Gaspero, Crespan, Meneghetti, Frare, Vignani, et al. 2010; Laucou, Lacombe, Dechesne, Siret, Bruno, Dessup, Dessup, Ortigosa, et al. 2011). Emanuelli, Lorenzi, Grzeskowiak, Catalano, Stefanini, and Troggio (2013) concluded that "further studies of grapevine genetic data are required and that existing genetic databases may not be the useful reference standard" they were believed to be.
This is why some experts, such as Marisa Fontana and Roberto Bandinelli, believe that researchers might do better to visit areas where varieties naturally grow, verify that the grapevines under examination do have ampelographic characteristics typical of the variety they are studying, and then obtain genetic profiles of which they are certain, rather than relying simply and only on preexisting ampelographic databanks available in their home region or country, where the standard grapevines may have been misidentified. Clearly, this is an expensive proposition, and therefore leaves many cold. Still another problem with ampelographic identifications is that often too few accessions are examined. Most published studies report mind-numbing, long lists or tables of SSR microsatellite results performed on many different grape varieties, but often, carefully reading the results reveals that just a single accession or two has been studied for each grape variety, and that seems much too little.
An especially big problem in Italy is that most of the old vineyards are made up of promiscuously planted grapevines: even if farmers tell you that "this is an old vineyard of Aglianico," the chances are high there will be Piedirosso, Aglianicone, Tronto, and maybe even white grape varieties planted there. So unless quite a few of the vines in that vineyard are studied, mistakes are likely. One such problem variety is Verdello, grapevines of which apparently grow in different regions of Italy, alongside many cultivars named Verde-Something or Verde-like. It's quite likely that not all the "Verdello" grapevines in a given vineyard really are Verdello. Farmers often gave a "green-name" to any grapevine that generically fit the bill (and they still do so). Thus when sampling Verdello grapevines, the likelihood of picking up a vine that really isn't Verdello is high, and the skill of the ampelographer becomes of paramount importance. If the ampelographer mistakenly identifies one of the vines as Verdello (in a vineyard that likely contains many similar-looking but altogether different varieties), the DNA profile of that grapevine will be taken to be that of Verdello; this DNA profile will then be the reference DNA data for that research group's databank. Unfortunately, if the ampelographer mistakenly identified as Verdello a similar looking but actually altogether different grape, then future studies will inevitably conclude that Verdello (or what they wrongly believe to be Verdello) is identical to yet another grape that will be found to have the same DNA. This is how, perhaps years later, a researcher in another country might erroneously conclude that a local grapevine "X" is in fact Italy's Verdello, when in fact it is not, because the DNA considered to be that of Verdello wasn't Verdello's in the first place. Which leads to that nation's grape "X" being eliminated, and called Verdello from then on. Unfortunately, there are numerous examples of erroneous attributions, and these are a huge problem because they convey essentially wrong information as a certitude, thanks to the "end-all" that is genetic testing. Researchers always conclude in their studies that their findings require that the National Registry be changed or updated. Those changes might not take place immediately, but in the meantime everyone refers to the study that "determined" that two previously distinct varieties are identical. The risk is a restructuring of the Italian (and not just Italian, of course) ampelographic platform that rests on at times very sketchy data. In my opinion, there is currently a real danger of what I have defined as excessive revisionism of grape history, an attitude that privileges concluding that "this grape is not the grape you always thought it was."
Excessive Reductionism: When Is Identical Really Identical?
Besides excessive revisionism, excessive reductionism ("These two, or three, or four, etc., grape varieties are all the same") is another potential problem. It is why some modern counts of Italy's native grapes list fewer than four hundred varieties, and why many local grape scientists believe that number to be much too low. As we have seen, genetic profiling involves analysis of DNA sequence repeats that scientist have always believed are not transcripted (copied) and transcribed (translated), or in other words, are not coded for anything. In fact, scientists are becoming increasingly aware that even the sequences of DNA that we once thought did not code for anything are in fact a lot more active than originally believed. Hence, even those portions of DNA that microsatellite testing uses to determine identity between varieties are not in fact quite as identical as we like to think they are.
One of the most interesting aspects in all of wine is the existence of biotypes or subvarieties (others use these two terms interchangeably with clones, but this is incorrect), meaning those varieties that are supposedly genetically "identical" but have obvious morphologic and physiological differences. Biotypes are members of a grape variety that have spread out geographically and adapted to different environments over the centuries (for more on them, see chapter 2). In so doing, they have built up mutations. These mutations, depending on where they affect the genome, may or may not have important consequences; clearly, the older the variety is, the more chances it has of undergoing mutations, thereby developing a slew of descendants that look and behave differently. In this sense, it's not that some varieties are more prone to mutation than others, just that they have been around longer. Pinot Nero and Nebbiolo come to mind: it's not that these two mutate more easily than others, as has always been believed, but rather that they are very old grape varieties.
Based on microsatellite analysis, Pinot Nero, Pinot Grigio, and Pinot Bianco have the same genetic profile, but all look obviously different: one has dark blue berries, another red-pink berries, and one white (actually yellow-green) berries. Clearly, no wine lover thinks of the various Pinot grapes and wines as being identical, but in fact, at the present state of knowledge, microsatellite testing tells us they are. It's much more difficult to distinguish between, for example, Italy's Cataratto Bianco Lucido, Cataratto Bianco Extralucido, and Cataratto Bianco Comune, because the morphologic differences present are a great deal more obscure, and limited mainly to differences in berry appearance. According to DNA microsatellite studies, all three are genetically identical: but while all of us consider the three Pinots to be completely different grape varieties, it's admittedly difficult to feel the same way about the Catarattos.
The world of Italian grapes is filled with many "different yet not so different-looking" grapes. Pigato, Favorita, and Vermentino are another case in point. Pigato grows in Liguria, Vermentino in both Liguria and Sardinia, and Favorita in Piedmont. The three grapes have been deemed genetically identical based on DNA microsatellite results (as the three Pinots have), but the vast majority of Ligurian producers (especially) refute this notion-and let me tell you, quite vociferously at times.In fact, you can't blame them, since there are obvious physical differences between the three grapes, but apparently their morphological differences are not considered sufficient to separate the three varieties as distinct. However, I am not so sure there are only minor consequences for the wines, because I find Pigato wines recognizably different from Vermentinos most of the time, and from Favorita even more often. Pigato and Vermentino in Liguria often share the same vineyard parcel, and yet, to my taste, their wines do smell and taste sufficiently different to warrant at least raising an eyebrow or two. Angelo Negro, one of the best producers of Roero in Piedmont, told me recently how years ago he planted both Pigato and Favorita side by side in a vineyard (because a university expert he had told him the varieties were identical), but that both the grapevines and the wines made from them couldn't have turned out more different. Now there's food (er, wine) for thought.
Given how complicated the world of Italian native and traditional grapes is, with myriad slightly-different looking grapes that are said to be "genetically similar," this becomes a very important question. So, just how different does a cultivar have to be, to be considered distinct? And when we say-or are told-that varieties are "genetically identical," do we know exactly what that means? This is not at all a moot point, since we know that the different phenotype expressions of biotypes do have a genetic background: for example, analysis of up to one hundred DNA markers (which in practice is never done) showed that a few genetic variations can be observed among clones of Pinot, as with Chardonnay (Riaz, Garrison, Dangl, Boursiquot, and Meredith 2002). So what would we find if we sequenced out the entire genome of the Catarattos, or of Pigato/Vermentino/Favorita? Well, we might find that the genetic differences between them are far more widespread than we currently believe them to be.
In fact, even when DNA looks totally identical, it may function, or be made to function, in completely different manners, leading to completely different results. DNA is far more complex than scientists initially believed: in fact, over the last thirty years it has become increasingly apparent that we still don't know enough about the nucleic acids (both DNA and RNA) and their many intricate functions and interrelations. At the present state of genetic knowledge, when DNA profiling shows that two grapevines have the same microsatellite repeat sequences, scientists conclude that the two grapevines are identical. I wonder. For example, we have learned that those portions of DNA that supposedly don't code for anything, defined by scientists as "junk DNA" or "nonsense DNA," which DNA profiling using the microsatellite technique relies upon for its results, actually are not passive at all. They may all look the same, but they don't necessarily work the same way. Hence, it cannot be excluded that the end result of their activity may lead to altogether different results, in this case, what ultimately are distinct grape varieties. For example, even portions of junk DNA are transcribed (copied) into RNA molecules with different functions. RNA does a lot more than act only as a messenger and a translator. Rather it exerts an influence on DNA at many levels, regulating gene activity and expression: it can do so not just during transcription and translation, but at post-transcriptional and post-translational levels as well. In fact, while we tend to think of our world as governed by DNA, RNA is just as important, and perhaps even more. Besides the well known mRNA and tRNA, other RNA molecules have been recently described, for example mRNA molecules that, despite their name, do not seem to transport any specific message. All these RNA molecules can exert control over what the DNA ultimately does, but they are themselves subject to various control mechanisms. How and why these RNA molecules interact with DNA is the subject of research studies in laboratories and universities all over the world.
Clearly, the genome is far more complex than we once thought: for instance, the present definition of gene as that portion of DNA which codes for a protein is undoubtedly limited. Using that definition, for example, only 2 percent of human DNA is made up of genes, and that's just not possible, for there are many more portions of DNA that are quasi-genes, which either do something or are made to do something by interaction with appropriate RNA molecules of various kinds. Returning to our grape varieties example, it follows that today we take microsatellite profiles at what might be described as only face value: when confronted with similar DNA microsatellite profiles, we conclude that similar sequences are in fact the same, and hence that the vines that share them are identical. But as we have seen, that is extremely unlikely, for though those DNA sequences all look the same, they may be transcribed and eventually translated in very different manners, leading to what are essentially different-looking and perhaps even distinct grape varieties. Therein may lie an explanation why, for example, Pigato, Vermentino, and Favorita, though genetically "identical" at our present state of knowledge, look different and produce different-tasting wines: because they are in fact distinct varieties. Which would also mean that many older farmers out there really do know best. In any case, Pelsy, Hocquigny, Moncada, Barbeau, Forget, Hinrichsen, and Merdinoglu. (2010) have concluded that when clones of the same variety have phenotypes different enough to lead to the production of different wines, they are to be grouped into different cultivars. Furthermore, Emanuelli, Lorenzi, Grzeskowiak, Catalano, Stefanini, and Troggio (2013) have stated that accessions sharing the same SSR profile ought to be evaluated further before being eliminated from standard grapevine collections, because they might not be redundant at all.
Therefore, in my opinion, though at this time we cannot say that Pigato/Vermentino/Favorita or Cataratto Comune/Lucido/Extralucido are in fact distinct varieties, we should at least always stress that they are different biotypes and hence, their resulting wines can be different, to greater or lesser degrees depending on the varieties involved.