Genetic Diversity in Remnant Swedish Hop (Humulus Lupulus L.) Yards from the 15Th to 18Th Century
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Genetic Diversity in Remnant Swedish Hop (Humulus lupulus L.) Yards from the 15th to 18th Century Else-Marie Karlsson Strese, Maria Lundström, Jenny Hagenblad and Matti W. Leino Linköping University Post Print N.B.: When citing this work, cite the original article. The original publication is available at www.springerlink.com: Else-Marie Karlsson Strese, Maria Lundström, Jenny Hagenblad and Matti W. Leino, Genetic Diversity in Remnant Swedish Hop (Humulus lupulus L.) Yards from the 15tht to 18th Century, 2014, Economic Botany, (68), 3, 231-245. http://dx.doi.org/10.1007/s12231-014-9273-8 Copyright: Springer Verlag (Germany) http://www.springerlink.com/?MUD=MP Postprint available at: Linköping University Electronic Press http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-109296 1 Genetic diversity in remnant Swedish hop yards from the 15th to 18th century Else-Marie Karlsson Strese1, Maria Lundström2, Jenny Hagenblad2 and Matti W Leino1,2* 1 Nordiska museet - Swedish Museum of Cultural History, SE-643 98 Julita, Sweden 2 IFM-Biology, Linköping University, SE-581 83 Linköping, Sweden *Corresponding author: Matti W Leino, email: [email protected], phone: +46 8 51954575 Keywords: brewing, crop migration, dioecious plants, historic maps, microsatellites, plant longevity, Humulus lupulus L. 2 Abstract Hop (Humulus lupulus L.) is a perennial plant cultivated for its use in beer production. The plant is dioecious and the female plants produce cones containing substances that enhance the taste and durability of beer. Beer was long an essential part of food supply in Northern Europe, and hop has thus been a very important crop during the last 1000 years. In Sweden, hop cultivation was, by law, mandatory for farmers from 1414 till 1860. Today, Swedish hop cultivation is negligible but historical remnant hop plants can still be found as feral populations. Using historical maps and document we have located ten historical hop yards from the 15th to 18th century where hop plants still persist as now feral populations. Some fifteen plants of each population were sampled and genotyped with ten SSR markers and one marker diagnostic for sex type. In addition 25 genebank preserved clones of older landraces and cultivars from Europe were genotyped. Genotyping results show abundant clonality and low rates of sexual reproduction within the feral populations. Two of the populations had markedly higher genetic diversity and a higher number of haplotypes, and in these populations a mix of female and male plants was also found. The populations were all clearly differentiated with no haplotypes shared between populations and little evidence of exchange of genetic material. These results indicate that natural spread and genetic recombination is uncommon or slow in Sweden and that the feral plants could be remnants of the original historical cultivations. In the assembly of European genebank clones several clones showed identical genotypes and overall limited genetic diversity. The Swedish populations were in most cases genetically clearly different from the genebank clones. This contrasts with historical records of massive introductions of hop clones from continental Europe during the 19th century and shows that these imports did not replace the original hop cultivated. A possible better adaption of the Swedish hops and primitive historical breeding are discussed. 3 Humle (Humulus lupulus L.) är en flerårig växt som odlas för användning i ölproduktion. Växten är tvåbyggare och honplantorna producerar kottar som innehåller ämnen som förbättrar ölets smak och hållbarhet. Öl var länge en viktig del av livsmedelsförsörjningen i norra Europa, varför humle varit en mycket betydelsefull gröda under de senaste 1000 åren. I Sverige var humleodling enligt lag obligatorisk för jordbrukare från år 1414 till 1860. I dag är den svenska odlingen av humle försumbar men förvildade humleplantor från historiska odlingar kan fortfarande hittas. Med hjälp av historiska kartor och dokument har vi återfunnit tio historiska humleodlingar från 1400- till 1700- talet där humleplantor kan återfinnas. Prov togs från ett femtontal plantor av varje population och genotypades med tio SSR markörer och en markör diagnostisk för kön. Dessutom genotypades 25 kloner av gamla lantsorter och sorter från Europa bevarade i genbanker. Resultaten visar på hög grad av klonalitet och låg frekvens av sexuell reproduktion inom populationerna. Två populationer hade markant högre genetisk diversitet och ett större antal haplotyper, i dessa populationer förekom också en blandning av han- och honplantor. Populationerna var alla tydligt differentierade från varandra och inga haplotyper förkom i mer än en population, vilket påvisar lågt utbyte av genetiskt material. Dessa resultat tyder på att naturlig spridning och genetisk rekombination är ovanligt eller långsamt i Sverige och att de nu förvildade växterna kan vara rester av de ursprungliga historiska odlingarna. Analysen av de europeiska klonerna från genbanker visade att flera kloner hade identiska genotyper och totalt sett begränsad genetisk diversitet. De svenska populationerna var i de flesta fall genetiskt klart särskiljbara från genbanksklonerna. Detta resultat motsäger historiska dokument som beskriver massiv introduktion av humlekloner från kontinentala Europa under 1800-talet och visar att denna import inte ersatte den humle som tidigare odlats. En möjlig bättre klimatanpassning av de ursprungliga svenska humlesorterna och en möjlig primitiv historisk förädling diskuteras. 4 Introduction Hop (Humulus lupulus L.) is a climbing perennial plant. It is cultivated for the production of its cones, to be used in beer brewing. The plant is dioecious with separate male and female plants, and female plants are exclusively cultivated as they alone produce the cones. Male plants, in contrast, have throughout history been banned from the neighborhoods of hop yards (Barth et al., 1994; Bromelius, 1687). Propagation of hop under cultivation is mainly performed vegetatively, through cuttings, the plants are competitive and clones can potentially be very old. However, like many plants with a strong vegetative reproduction, in particular dioecious plants, questions regarding the longevity and population dynamics are yet unanswered (de Witte and Stocklin, 2010; Solé, 2003). In beer producing countries in Europe hops was long an essential part of food supply. Historically, beer was not just a thirst-quenching beverage, but also a calorie rich food, a “liquid bread” (Barth et al., 1994). In the Nordic region, with its short growing season and cool and humid climate, it was often difficult to harvest cereals fully ripe and dry. Grain with pre-harvest sprouting could not be stored, but was instead used for brewing and thus not wasted. Hops did not only add flavor to the beer but also had preservative effects from substances produced by glands in the cone. Consequently, hop was during more than 1000 years an indispensable crop in Northern Europe (Unger, 2004). It is not known how long hop has been cultivated in Sweden, but hop pollen from 7th century (Lagerås, 2003) and macro fossils from the 8th century (Heimdahl, 1999; Heimdahl, 2002) have been found. The earliest written historical primary information is from the 12th century (Tollin and Karlsson Strese, 2007). In Sweden, hop cultivation was mandatory for each 5 farmer and prescribed by law from 1414 till 1860. As a consequence of this law, hop cultivation was frequently reported in financial, juridical and many other historical documents. Historical sources from the 17th century and onwards, provide information about the introduction of hop cuttings into Sweden from areas mainly in current Germany, Poland and the Czech Republic (Bromelius 1687; Broocman 1736; Granhall 1951). During the 17- 18th centuries hop culture was at its most extensive. During the 1800s extensive trials were conducted, often initiated by agricultural societies, who imported and planted large numbers of cuttings especially of the variety Saarz (Anonymous, 1858; Jonsson, 1883; Spaak, 1880). Cultivation of hops declined in Sweden towards the end of the 19th century. During World War I and II the access to imported hop was limited and a breeding program and cultivation was initiated in the southeast of Sweden (Granhall, 1951). After the wars hop cultivation ceased completely and the last commercial cultivation and breeding programs ended in 1959. In the year 2000 the national program for diversity of cultivated plants (POM) was established in Sweden. The purpose was to ensure the long-term survival and sustainable use of cultivated plant resources in Sweden. The main tasks of the program are to inventory, collect and preserve clonally propagated cultivated plants. For the inventory of hop the wealth of historical source data was used to localize and verify remnants of cultivated hop (Karlsson Strese et al., 2010). At the location of many old hop yards, nowadays abandoned and covered by extensive forests, hop still grows untended by man. A range of questions can be asked regarding the now feral hop populations and their development since active cultivation was discontinued. Although plants grow on the same sites as where historical cultivations once occurred, the plant material might have changed over time. Remnant plant material might also have been over stamped by later introductions 6 and re-plantations of hop yards. Another critical question is whether the populations have clonal growth, are the product of sexual propagation