What is the Scientific Truth About Garlic Varieties?
Updated: Dec 17, 2019
Garlic, The Scientific Truth About Garlic Varieties
Garlic (Allium sativum) is a plant producing an edible bulb, made of storage leaves known as cloves. It is of Asian origin, being Allium longicuspis considered its wild ancestor. Besides being appreciated in cooking as common seasoning for thousands of years garlic, is also used in pharmacology and cosmetics. Indeed, it is known to have medical properties, protecting against different diseases; for instance, hypercholesterolemia, hypertension, atherosclerosis, and thrombosis, reducing the risk of developing cardiovascular disease.
Hundreds of garlic cultivars are available from garlic farms, seed companies and germplasm collections. There is a high degree of variability in bulb shape, clove wrapper color, bulb size, yield, and flavor of each garlic cultivar. Garlic classification can be overwhelming, as garlic characteristics such as size, taste, shape, color, sulphur compounds, number of cloves per bulb, pungency, storage time and growing requirements, can be influenced by environmental factors. Garlic appears to be very receptive to variations arising from non genetic influences on gene expression. Science, through genetic testing, helps us determine garlic differences.
In 2003, garlic genetic testing by Dr. Gail Volk (USDA in Colorado) and Dr. Joachim Keller (Institute of Plant Genetics and Crop Plant Research in Gatersleben, Germany) independently identified ten (10) different ‘families’ or sub-varietal groups of garlic. These ten types are Porcelain, Purple Stripe, Marbled Purple Stripe, Glazed Purple Stripe, Rocambole, Creole, Asiatic, Turban, Artichoke, and Silverskin. Keller and Volk ten distinct groups are as follows:
Three varieties of "weakly bolting" hardnecks that can produce softnecks - Creole, Asiatic and Turban.
Two distinct softneck varieties; Artichoke and Silverskin.
Five hardneck varieties called Porcelain, Purple Stripe, Marbled Purple Stripe, Glazed Purple Stripe, and Rocambole.
In 2005, Dr. Volk and David Stern of the Garlic Seed Foundation led a project in which 10 cultivars, one of each of the 10 types, were grown by garlic farmers in twelve locations around the United States and Canada. The cultivars were ‘Ajo Rojo’, ‘Chesnok’, ‘German White’, ‘Inchelium’, ‘Purple Glazer’, ‘Red Janice’, ‘Sakura’, ‘Siberian’, ‘Silverwhite’, and ‘Spanish Roja’. The small-scale farmers were provided with planting stocks from the same original sources and were asked to grow them on their farms for two consecutive years using their best practices. At the end of the study, harvested bulbs were analyzed for quality, wrapper color, yield, clove characteristics, and elemental composition.
Read the article on Genetic Diversity among U.S. Garlic Clones as Detected Using AFLP Methods by Gayle M. Volk, Adam D. Henk, and Christopher M. Richards. http://garlicseedfoundation.info/jashsgarlic.pdf
The recent emergence of genotyping-by-sequencing (GBS) approaches, like DArTseq, can be used to characterize garlic genetic diversity. In 2017, high-resolution genotyping identified 286 unique and 131 redundant garlic types. Researchers began with a collection of garlic known as the germplasm-bank core collection. To the best of our knowledge, this is the first report of high-throughput genotyping of a large collection of garlic plant cells. This is particularly interesting for garlic growers. The assessment of Genetic Diversity of garlic (Allium sativum) by "Genotyping-by-Sequencing” has lead researchers one step further in understanding garlic types and varieties.
A Garlic Germplasm are living genetic resources such as cloves, or garlic tissues that are maintained for the purpose of preservation, and other research uses. Garlic germplasm collections exist around the world including one located at the National Plant Germplasm System’s Allium - at the ARS Western Regional Plant Introduction Station in Pullman, Wash. Here they maintain, describe and distribute 293 garlic specimens (16 primitive garlics, 207 leeks, 44 chives, and 579 wild, ornamental and native Allium species). This novice research, performed in 2017, provides even more valuable information than the DNA research performed more than twenty years ago.
Researchers started with 417 garlic samples, and these samples were analyzed using SilicoDArT markers (representing presence/absence of restriction fragments in DArT genomic representations) and SNP data. The markers allowed identifying 286 unique and 131 redundant garlic samples. Hierarchical-cluster analysis, principal-coordinates analysis and STRUCTURE showed general consistency, generating three main garlic-groups, mostly determined by variety and geographical origin. In addition, high-resolution genotyping identified 286 unique and 131 redundant accessions, used to select a reduced size germplasm-bank core collection. Through their analysis, the research team significantly reduced the analyzed garlic germplasm-bank size, identifying redundant garlic types and thus generating a unique core collection of garlic.
In another study completed in 2018, Chinese researchers collected 92 garlic landraces from China and 10 from other countries (Supplementary Table S1). Thus, in total, 102 landraces were planted in the experimental farm. Twelve plants of each landrace were grown in one row for tissue sampling. The experimental farm, sowing date, and planting density were the same as those used for phenotypic measurements. The growth of the bulbs was observed in five plants from each row. At the end of the growing season, researchers and scientist in China, used DNA sequencing and Genotyping technologies
to characterize the population variation. All 102 landraces were subjected to Illumina RNA sequencing individually. Total RNA from each sample was used to construct cDNA libraries. In their conclusion, they investigated three Clove shape traits (CSTs) in the 102 landraces of garlic collected from China and other countries and found that the three clove shape traits varied extensively among the 102 landraces. They observed a significant correlation among three traits suggesting they were mutually dependent. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6289775/
In another study in 2017, a total of 417 a priori different garlic entries collected in Spain (some of them being originally derived from other countries) were used for DArTseq analyses: 408 from the main Garlic-Germplasm Bank at “Instituto Andaluz de Investigación y Formación Agraria, Pesquera, Alimentaria y de la Producción Ecológica” (IFAPA) of “Junta de Andalucía” in Cordoba; five from Cordoba University (C1 to C5); and four (G, K, L, and M) from “Centro de Ensayos de Evaluación de Variedades” at “Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria” (INIA) in Madrid (Supplementary Table S1). Garlic leaves were frozen in liquid nitrogen and stored at -80°C until needed. Three different analyses were performed, in order to study genetic diversity and structure of germplasm-bank accessions. After creating the SNP and SilicoDArT marker scoring matrices, a Gower’s distance matrix was generated. They found that Spanish varieties were more related between them than to Chinese varieties, which were closely related.
The main reason apples aren’t grown from seed is that they don’t “come true to seed.” Just like humans, the offspring may have some resemblance to their parents, but with their own flavor and habits. Garlic on the other hand, is true to seed. Garlic is typically propagated through cloves, which are clones of the plant. Cloves are planted in the fall to produce bulbs the following summer. Some hardneck varieties can be forced to flower, and set or make true Garlic Seed. This seed results in new varieties of garlic, but very few people worldwide are engaged in this work because it is so time consuming.
There are hundreds of named garlic cultivars grown across the United States and Canada. A few examples include Bogatyr, Chesnok Red, French Pink, Northern White, German Extra-Hardy, Georgian Fire, Metechi, Music, Krasnodor Red, Russian Red and Spanish Roja. Many of these are similar in appearance; After close inspection, even by a novice, it is evident clove arrangement, number of topsets, topset size, topset color, number of cloves, clove weight, clove skin color, and clove skin tightness, were generally the same. At our garlic farm in Bozeman, Montana (GroEat Farm), we grow ten+ different garlic cultivars and it is possible, some of the types, are genetically the same? For example, German Extra-Hardy and Northern White are very similar; both have virtually the same appearance with large, beautiful and well-formed bulbs. The plants are virtually indistinguishable when growing in the spring and summer. The flavor of both is zingy, strong and robust and sticks around for a long time. Once we determined the types that we liked best, we begin to propagate our own stock, selecting the biggest and best bulbs to plant the next year. In this way, we developed our own strain adapted to our conditions in Bozeman, Montana.
Agricultural practices usually involve cultivation of a reduced number of species and varieties, which may lead to genetic erosion. In our opinion, it is important to maintain garlic germplasm banks as reservoirs of genetic variability for crop breeding. These collections may harbor genetic potential to improve productivity and adaptation/resistance to stresses such as drought and diseases.
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Jere Folgert is the owner of GroEat Garlic Farm in Bozeman, Montana. GroEat Farm is a small, sustainable family farm located in the beautiful Hyalite Foothills, in the shadows of the Gallatin Mountain Range. The hardneck varieties that they grow on their farm flourish, due to the combination of the cold winters, temperate summers, moist spring, and the dynamic alluvial soils, washed down from the Gallatin Range.