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Review

Worldwide Research Trends on Wheat and Barley: A Bibliometric Comparative Analysis

1
Department of Biotechnology-Plant Biology, School of Agricultural, Food and Biosystems Engineering, Universidad Politécnica de Madrid, 28040 Madrid, Spain
2
Department of Engineering, University of Almeria, Crta, Sacramento s/n, 04120 Almeria, Spain
*
Author to whom correspondence should be addressed.
Agronomy 2019, 9(7), 352; https://doi.org/10.3390/agronomy9070352
Received: 10 May 2019 / Revised: 24 June 2019 / Accepted: 29 June 2019 / Published: 3 July 2019
(This article belongs to the Special Issue Wheat Breeding: Procedures and Strategies)

Abstract

Grain cereals such as wheat, barley, rice, and maize are the nutritional basis of humans and animals worldwide. Thus, these crop plants are essential in terms of global food security. We conducted a bibliometric assessment of scientific documents and patents related to wheat and barley through the Scopus database. The number of documents published per year, their affiliation and corresponding scientific areas, the publishing journals, document types and languages were metricized. The main keywords included in research publications concerning these crops were also analysed globally and clustered in thematic groups. In the case of keywords related to agronomy or genetics and molecular biology, we considered documents dated up to 1999, and from 2000 to 2018, separately. Comparison of the results obtained for wheat and barley revealed some remarkable different trends, for which the underlying reasons are further discussed.
Keywords: crop; cereals; agronomy; genetics; bibliometry crop; cereals; agronomy; genetics; bibliometry

1. Introduction

Wheat (Triticum spp.) and barley (Hordeum vulgare L.) are two cereal crops that belong to the family Poaceae (order Poales). Wheat is a staple source of nutrients for around 40% of the world’s population. Barley is mainly used for animal feed and for brewing, although it is also considered a principal food in regions where other major cereals cannot be grown.
The cultivation of wheat reaches far back into history. Wheat was one of the first domesticated food crops and for 8000 years has been the main food of the major civilizations of Europe, West Asia and North Africa. This is likely because of wheat’s agronomic adaptability, ease of grain storage and ease of converting grain into flour for making many different foods [1]. Currently, wheat is the most widely grown crop in the world, on more than 218 million ha, and its world trade is greater than for all other crops combined. Wheat occupies a central place in human nutrition providing 20% of the daily protein and food calories. In terms of food security, it is the second most important food crop in the developing world after rice, because an estimated 80 million farmers rely on wheat for their livelihoods [1].
Roughly 90 to 95% of the wheat produced in the world is common or bread wheat (Triticum aestivum L. 2n = 42, hexaploid, AABBDD genomes), which can be classified as hard wheat or soft wheat, depending on the grain hardness. Bread wheat is utilized mainly as flour (whole grain or refined) for the production of a large variety of leavened and flat breads, and for the manufacture of a wide variety of other baked products. The total world production also includes about 35–40 million tonnes of T. turgidum L. var. durum Desf. (2n = 28, tetraploid, AABB genomes), which is well adapted to the hot, dry conditions surrounding the Mediterranean Sea and similar climates in other world regions. This species is mainly used for making pasta and is often referred to either as “pasta wheat” or “durum wheat”. Some durum wheat is milled into flour to manufacture medium-dense breads in Mediterranean and Middle Eastern countries and some into coarse durum grain grits used to produce couscous (cooked grits) in Arab countries [2]. Other wheat species are less cultivated although they play a major role in the expanding market in health foods. These are einkorn (T. monococcum L. subsp. monococcum, diploid, AA genomes), emmer (T. turgidum L. var. dicoccum, tetraploid, AABB genomes), and spelt (T. aestivum subsp. spelta (L.) Thell, hexaploid, AABBDD genomes). Spelt, emmer, and most forms of einkorn differ from bread and durum wheats in being hulled, that is, the glumes remain tightly closed over the grain and are not removed by threshing [3].
Wheat is the most important source of carbohydrate in a majority of countries, and, globally, it is the leading source of vegetal protein in human food, having a protein content of about 13%, which is relatively high compared to other major cereals. Wheat, eaten as a whole grain, is also a source of micronutrients and dietary fibre, it contains minerals, vitamins and fats (lipids), and with a small amount of animal or legume protein added is highly nutritious [3,4,5]. A predominately wheat-based diet is higher in fibre than a meat-based diet [6]. It is noteworthy that many health claims approved by EFSA relate to fibre components in cereals, including wheat and barley and in their positive effects on intestinal function, glucose responses, or cholesterol control [7]. The most detailed study about the significance of wheat nutrition was carried out as part of EU Framework 6 in the HEALTHGRAIN programme [8].
Doughs produced from bread wheat flour differ from those made from other cereals in their unique viscoelastic properties [9]. The raised bread loaf is possible because the wheat kernel contains gluten, an elastic ensemble of proteins that traps minute bubbles of carbon dioxide when fermentation occurs in leavened dough, causing the dough to rise [10]. Regarding human health, the gluten polymer is related to coeliac disease, a chronic inflammation of the bowel that leads to malabsorption of nutrients, estimated to affect 1% of Western Europe’s population [11]. Other diseases related to wheat have been described, such as respiratory and food allergies, which have promoted a lot of wheat research in the area of human health.
The consumption of wheat is increasing globally, even in countries with climates unfavourable for wheat production. But wheat is also a popular source of animal feed, particularly in years where harvests are adversely affected by rain and significant quantities of the grain are unsuitable for consumption. Such low-quality grain is often used by industry to make adhesives, paper additives, and several other products, even alcohol [1].
Barley (Hordeum vulgare ssp. vulgare L. 2n = 14, diploid, HH genomes) is among the world’s earliest domesticated crop species, being cultivated in the Nile River Valley of Egypt at least 17,000 years ago [12,13]. A post-domestication change resulted in the presence of a naked cariopsis. The mutation that resulted in this change is thought to have occurred in the Middle East around 8000 BC but gradually spread to other regions so that hulless (naked) barley grains have been found in archaeological digs in Northern Scotland [14,15]. Barley was viewed as a nutritious food and Roman gladiators were known as hordearii (barley men) because it formed part of their training diet. Wheat gradually replaced barley as a major food cereal due to the increased numbers of grains per ear and free threshing [16].
Currently, barley is the fourth most important cereal crop in the world, grown in more than 100 countries. In the last decade, Europe has produced around 60% of the world tonnage of barley, with Asia and the Americas producing 15% and 13%, respectively [17]. Barley has a haploid genome size of ~5.3 Gb distributed over seven chromosomes. Due to its simple inbreeding diploid genetics, barley is an excellent experimental model for other temperate cereals, such as wheat, which have much bigger (17 Gb) and more complex polyploid genomes. Barley shows a good level of adaptability to unfavourable environments like cold, drought, or poor soils, and is considered more tolerant than wheat to adverse growing conditions [18].
Barley grains are mainly used for animal feed and in the production of alcoholic beverages. While feed is the main use of the barley crop, the malting barley crop is far more valuable, i.e., farmers generally receive a significant premium when selling their barley harvests to the malting market. Barley has been associated with beer production for a very long time. Traces of beer products can be found in pottery dated back at least 9000 years and brewing is thought to have existed on an organized scale in pre-Dynastic Egypt 7000 to 5000 years ago. By 2014, world beer consumption had grown to over 1960 million hectolitres, equating to over 21.5 million tonnes of malt, at an average conversion rate of 11 kg malt to 1 hectolitre of beer [19]. Similarly, Scottish distillers, the major users of barley in the distilling segment, have increased production of malt whisky over the same period [20].
The current interest in wheat research is supported by the establishment in 2011, under the aegis of the G20 Ministries of Agriculture, of the Wheat Initiative [21]. This initiative was created for coordinating international research efforts on wheat to address the challenges raised by the fact that in recent years, wheat production levels have not satisfied demand, triggering price instability, hunger riots, and government instability. With a predicted world population of over 9 billion by 2050 [22], the demand for wheat will increase by 60% compared with 2010. To meet this demand, global annual yield increases must rise from the current 1% per year (2001–2010) to 1.6% per year (2011–2050). In the case of barley, researchers, growers, processors and producers have supported the creation of the International Barley Hub [16], a world-leading centre with the aim to translate excellence in barley research and innovation into economic, social and environmental benefits.
Global food security, threatened by climate change and an increasing population, is one of the most important challenges in the 21st century, which has to be addressed while coping with an already stressed environment [23]. Given their major role in human and animal feed, wheat and barley production must increase but in a sustainable manner. This can be addressed through either the implementation of soil and crop management practices reducing the environmental impact of agroecosystems or by the genetic improvement of crop cultivars [24]. No-till or minimum tillage strategies, organic agriculture, intercropping and cover crops, smart fertilizers, drip irrigation and fertigation are all among the agronomic practices whose suitability to replace past agricultural intensification methods is being assessed [24,25,26]. Regarding plant improvement, the creation of more resilient varieties capable of achieving higher yields with less input requirements (water, fertilizers, etc.) has become a primary objective of cereal breeders. A better knowledge of the genetic basis of crop performance, especially under restricted or unfavourable conditions, is needed for the success of coming breeding programs. With that in mind, current projects worldwide are focused on understanding the molecular mechanisms involved in water and nitrogen uptake, assimilation, and utilization by cereals as key plant processes in crop sustainability [27,28]. Clearly, the use of modern biotechnology techniques will be required to develop such next-generation varieties. The availability, since 2012, of a barley genome reference sequence has allowed the earlier development of genomic tools in barley than in wheat, whose first high-quality reference sequence was not published until 2018 [29,30]. Understanding and exploiting the genetic diversity pooled in large collections of germplasm available for both species will be highly helpful for gene discovery and genome-assisted crop improvement [31,32,33].
The recent development of scientometrics [34,35], informetrics [36] and bibliometrics [37,38] has allowed the study of scientific trends in specific fields. In turn, these analytical techniques of scientific production are necessary for the assessment of the current state of research, as well as the contributions of researchers and countries in the fields of knowledge [37]. Furthermore, bibliometric indicators that measure the results of the scientific production in a specific field by a country or organization can also be considered as the economic and social indicators because a large amount of resources are invested in it [39]. Therefore, the aim of this work was to comparatively assess the historical evolution and current trends of research on wheat and barley by performing a descriptive and retrospective bibliometric study on the worldwide scientific production on these two major crops. An earlier study indicated that the journal coverage is higher in Scopus than in Web of Science [40]. In addition, numerous research articles have suggested the advantages of using Scopus to implement a bibliometric analysis [41,42]. Therefore, the Scopus database was selected. Given that massive information downloads are not possible from other databases such as PubMed, these databases are not useful to carry out bibliometric studies [43].

2. Methods

The research documents and patents analysed in this work were extracted from the Elsevier Scopus database. The search queries (TITLE-ABS-KEY({Wheat}) and (TITLE-ABS-KEY({Barley}) were used in January 2019 for collecting academic documents and patents including “wheat” or “barley” terms in the title, abstract and/or keywords.
The articles from the search were assessed and classified according to diverse aspects: number of documents per year, document type and language, distribution by subject categories and by journals, and affiliation by country and institution. The records obtained were analysed and the results were used to make graphs with the aim to display the results more conveniently.
The list of the 160 most abundant keywords in the documents retrieved, provided by the Scopus database after any search, was further analysed qualitatively and quantitatively. The terms listed were manually classified into four relevant thematic groups. The list provided after the initial search (i.e., main keywords considering all scientific documents dated up to 2018) was used to conduct the analysis of keywords related to cereals-and-model-plants and human-and-animals. In the case of terms related to agronomy and genes-and-proteins, two lists of keywords corresponding to the documents dated up to 1999 and from 2000 to 2018, were analysed for each crop. For conducting a more informative assessment on the relative importance of specific terms within the thematic clusters, duplicated words (e.g., singular and plural of a term) or synonymous terms (e.g., “chromosomes, plant” and “plant chromosome”) were fused as one keyword. The whole sets and the clusters of keywords were used to obtain word clouds from the free software WordArt (https://wordart.com/). In these clouds, font size of a given keyword represents the number of times it appears in literature records.

3. Results and Discussion

3.1. Evolution of Scientific Output and Distribution by Countries, Institutions, and Languages

The term “wheat” has been detected in the title, abstract or keywords of a total of 169,297 documents over the period 1835–2018, while “barley” has been identified in 50,140 articles from 1833. The number of studies dealing with “wheat” and “barley” has grown in a continuous way since the first publication. A remarkable increase in publications was noted for both research topics since the second half of the twentieth century (Figure 1).
The significant rise of academic reports about wheat and barley in recent years could represent the general increase of scientific publications, rather than a real growing interest of the scientific community in these crops. In order to explore the former possibility, a further analysis was conducted, limited to the documents published in English. Therefore, the ratio of documents dated up to 1999 and from 2000 to 2018 was calculated for total publications, and for publications including wheat or barley in the title, abstract and/or keywords. The results pointed out that the increment experienced for publications on wheat (ratio 1:1.94) is actually higher than the observed when the global scientific production is considered (ratio 1:1.66). On the contrary, the ratio obtained for barley (1:1.40) is below the average, at least within English documents. Articles related to wheat have outnumbered those related to barley every year since the earliest reports. A different trend on the evolution of the scientific interest in both crops can also explain that the differences are enlarging at a higher rate since 2004 (Figure 1). These metrics surely reflect either the greater agro-economic relevance of wheat, with a worldwide production 5-fold higher than that of barley (772 and 147 million tonnes of wheat and barley, respectively, in 2017; data from FAOSTAT, Jan 21, 2019), and the increasing concerns about crops used for human consumption.
However, the interest in wheat or barley research is not equally represented among countries. Wheat and barley have been the focus of research in 159 and 158 countries, respectively, again proving the worldwide relevance of these crops. Twenty-one countries contributed more than 1% of the scientific reports related to wheat and barley (Table 1). These countries together published about 77% of the total documents dealing with wheat (77.01%) and barley (77.28%). However, our results showed remarkable differences in the relative contribution of some countries to studies on each of these crops (Table 1, Figure 2). For instance, countries such as USA, China, India, France, Pakistan, Brazil and Mexico contribute more to wheat than barley research, while the opposite is observed for UK, Canada, Germany, Spain, Sweden, Denmark, Czech Republic and Finland. These results agree with FAO information about wheat and barley production by continents and countries [17]. According to this source, wheat and barley are mainly produced in Asia and in Europe, respectively (Figure 3a,c). The top ten list of wheat producers is headed by China and India (Figure 3b), which are not included in the list of main barley producers, where European countries, such as Germany, France and Spain, are, however, included (Figure 3d). It should be noted that several of the countries highly represented in wheat research are developing countries where wheat is one of the nutritional staples (e.g., China, India, Pakistan, Brazil and Mexico; Table 1). On the other hand, countries more interested in barley research are developed countries, mainly in Europe (UK, Canada, Germany, Spain, Sweden, Denmark, Czech Republic and Finland; Table 1), where the ecoclimatic conditions are more suitable for this cereal crop [44]. The fact that barley is essential for the production of beer, among the most popular beverages in Europe, may point to the influence of some particular socio-cultural habits on the scientific interests of each country.
The 20 most productive institutions studying wheat and barley in the period are analysed in Table 2. As expected according to the results mentioned above, the institutions with the highest numbers of publications related to wheat were from the US (4 institutions), China (7), Canada (2), France (1), UK (1), India (2), Netherlands (1) and Australia (1), while the corresponding institutions for barley publications were from Canada (4), US (4), Sweden (1), UK (1), Germany (1), Australia (2), Scotland (1), France (1), Denmark (4) and Netherlands (1). In the top twenty most productive research centres, ten institutions from the US, Canada, UK, Australia, France and Netherlands were on both the wheat and barley lists. The remaining institutions again reflect the marked differences in the countries’ research interest in these crops (Table 2). Nine out of the 20 top institutions leading wheat research are agroalimentary and agricultural research centres from developing countries, such as China and India, while agricultural centres placed in Europe (e.g., Sweden, UK, Germany, France, Scotland, Netherlands and Denmark) are among the most relevant in barley research. It should be noted that in 13th position is the Carlsberg Research Centre from Denmark, which is exclusively focused in the art of brewing (https://carlsberggroup.com/who-we-are/groundbreaking-research/).
Research studies on wheat and barley have been published in 43 and 35 different languages, respectively. As expected, because English is the international language of science and technology, this was the most used language to publish wheat (156,596 reports, which account for 91.52%) and barley documents (47,785 reports, which account for 94.42%) (Figure 4). In studies related to wheat, English is followed by Chinese (with a mere 3.17%), in accordance with the fact that China has published the second highest number of documents on wheat (Table 1). However, in studies related to barley, English is followed by German (1.5%), which also agrees with the fact that Germany was the country that published the third highest barley reports, behind two English-speaking countries (the US and UK, Table 1). It can be noted that wheat papers published in Chinese are six times more frequent than Chinese barley documents, which indicates again the higher interest of developing countries like China in wheat than in barley.

3.2. Subject Categories, Sources and Types of Publications

Publications on wheat research are distributed across 29 subject areas according to the Scopus classification. The largest number of documents is included in the agricultural and biological science area (102,629 records, 36.72%), followed by biochemistry, genetics and molecular biology (51,332 records, 18.36%), environmental sciences (20,517 records, 7.34%), medicine (19,220 records, 6.88%), chemistry (13,204 records, 4.72%), immunology and microbiology (10,315 records, 3.69%), engineering (10,056, 3.60%), earth and planetary sciences (7338, 2.63%) and chemical engineering (7084, 2.53%). Almost 90% of wheat publications are included in these nine areas (Figure 5). It must be noted that a single document can be assigned to more than one area.
Barley scientific documents are also distributed across 29 subjects. Eight of the top nine areas for barley are also among the most important areas for wheat research. Agricultural and biological science (34,714 records, 42.12%) is again the first area, and biochemistry, genetics and molecular biology the second (19,448 records, 23.60%). The third area is environmental sciences (4534 records, 5.50%), the fourth medicine (4492 records, 5.45%) and the fifth is chemistry (3123 records, 3.79%). The sixth area is immunology and microbiology (2,981 records, 3.62%), followed by veterinary (1717, 2.08%), earth and planetary sciences (1539, 1.87%) and engineering (1519, 1.84%). These nine areas account for 90% of barley publications (Figure 5).
As expected, results showed that research documents on wheat and barley are mostly published under the same categories and in a rather similar percentage. The only remarkable difference was the incorporation of the veterinary category among the top positions in barley, an area that has no relevance for wheat (Figure 5). This finding is in agreement with the high percentage of barley production that is used for animal feeding [44].
Regarding the number of publications by source, Table 3 lists the top 10 journals in which results from the wheat and barley research fields have been published in. Both lists only shared three journals, i.e., Theoretical and Applied Genetics, Euphytica, and Plant and Soil, which publish articles “with a clear genetic component and significant impact on plant breeding”, “modern and traditional plant breeding using transgenic crop plants and/or marker assisted breeding in combination with traditional breeding tools” and “plant–soil interactions”, respectively. The remaining journals with a high number of wheat publications are quite specific for cereals, crops and food. However, journals where barley documents are mainly published are journals whose scope includes varied aspects of plant biology. As significant exceptions, the first journal where barley research studies are found, Journal of the Institute of Brewing, publishes documents relating to brewing, fermentation, distilling, raw materials and by-products, and the third in the list, Animal Feed Science and Technology, is a unique journal publishing scientific papers of international interest focused on animal feeding. These journals cover the two main applications for barley: brewery and animal feed production.
The scientific documents about wheat or barley recovered from the Scopus database were classified into 15 document types. The four types with a percentage higher than 1% are “article”, “conference paper”, “review” and “book chapter” (Table 4).
“Article”, which accounted for 89.73% of total publications with 151,914 reports for wheat and 91.13% with 45,695 for barley, was the most common document type to publish results from the wheat and barley research fields. In second place, “conference paper” accounted for 4.27% with 7,229 reports on wheat and 2.77% with 1,387 on barley, followed by “review” with 4,388 reports on wheat (2.59%) and 1,466 documents (2.92%) on barley, as well as “book chapter” with 2,254 documents on wheat (1.33%) and 745 documents on barley (1.49%). These four document types accounted for 97.93% and 98.31% of total publications on wheat and barley respectively. Globally, the remaining types of documents, “book”, “conference review”, “note”, “letter”, “erratum”, “short survey”, “editorial”, “business article”, “report”, “retracted”, and “undefined” accounted for 2.07% and 1.69% of total publications, individually contributing between 0.003–0.46% for wheat and between 0.002–0.41% for barley (Table 4). The results prove that articles are preferentially used by most authors to publish their scientific findings in these fields.

3.3. Keywords

The main research subjects in a given manuscript are summarised by the keywords defined in it. Thus, the assessment of the keywords of scientific documents allows for the establishment of the research trends in a specific field [45]. A word cloud made with all 160 keywords that the Scopus database showed for the articles related to wheat or barley, analysed in the present report, are shown in Figure 6. As expected, “Triticum aestivum” and “Triticum” are the two keywords most represented in wheat documents, which is the taxonomic nomenclature of bread wheat, the most relevant wheat crop species (Figure 6a). Similarly, the keyword most used in the documents from barley research is “Hordeum”, the genus that includes cultivated barley, whose species name (Hordeum vulgare) is actually fourth among the keywords in barley documents (Figure 6b). The second and the sixth barley-related keywords most employed are “Triticum aestivum” and “wheat” respectively, showing the important relation between both crops, and that wheat is frequently used as a reference for discussion of barley research results. In both lists, “maize” is the most frequent keyword of a plant species other than wheat and barley. Its relevance in wheat and barley documents is surely related to the fact that maize is not only cultivated for human and animal consumption but is also the most produced crop worldwide. Furthermore, the maize genome was sequenced in 2009 and has been commonly used as a reference in barley and wheat genomics [46]. The keywords “human”, “animal” and “nonhuman” are quite abundant in documents related to either wheat or barley. However, while “nonhuman” and “animal” show similar frequency in both sets of documents, “human” shows a more relevant position in wheat than in barley documents. This is surely ascribable to the distinct primary uses of wheat and barley grains. “Genetics” appears as the most relevant among the scientific disciplines, which likely shows the pivotal role that the studies on heredity and variation of plant traits have always had on crop research. “Chemistry” is also a relevant discipline that might reflect the importance of grain composition on its nutritional quality and on the rheological properties of flour doughs in the case of wheat [47].
A deeper study has allowed us to organize the keywords into thematic groups. We could separate keywords into four clusters: related cereals and model plants, human and animals, agronomy, and genes and proteins (Figure 7, Figure 8 and Figure 9).
When the keywords noting plant species were metricized, results showed that barley documents included more varied plant species. Wheat is mainly associated with other “cereals”, such as “maize”, “barley”, “rye”, “rice”, etc. (Figure 7a), whereas barley is not only related to numerous cereals but also with many model species, such as “Arabidopsis”, “Brassica napus”, “Medicago sativa” and “Solanum tuberosum” (Figure 7b). This can be due to the fact that barley is considered a model species for temperate cereals and so it is frequently contrasted with other model plants [48]. Regarding the cluster grouping human and animal keywords, wheat is associated with numerous terms related to human food or health, such as “diet”, “gluten”, “glucose”, “dietary fibre”, “bread”, “flour”, “celiac disease”, “immunology”, “wheat–bran”, etc. (Figure 7c), while barley is principally associated with terms related to livestock animals such as “sheep”, “rumen”, “cattle”, “ruminant stomach”, “ovis aries”, etc. (Figure 7d). These results again indicate the distinct main use of wheat and barley production for human food and animal feed, respectively. In addition, wheat documents show more keywords related to biofuels, such as “lignin”, “cellulose” and “biomass”, than barley reports (Figure 7c,d), suggesting a higher interest in wheat than barley as a biofuel. However, this trend could change in the near future because barley is currently being studied as a promising biofuel source [49].
For keywords clustered into the agronomy and genes and proteins thematic groups, documents dated up to 1999 and from 2000 to 2018 were separately considered. This analysis showed that, among the more frequent keywords listed in the Scopus database, the number of terms related to agronomy markedly increased over the period 2000–2018 compared to the earlier period for either of these crops. In the case of wheat, documents up to 1999 included only basic terms, such as “nitrogen”, “soil” or “yield”, whereas more recent documents included up to 25 keywords (Figure 8). Most of these novel keywords refer to environmental issues impacting crop production or to soil–crop management and monitoring innovations, some of which are being explored in the context of cropping sustainability, i.e., “fertilizer application”, “crop rotation”, “climate change”, “irrigation”, “remote sensing”, “carbon dioxide”, “soil moisture”, “drought” or “tillage”. Far fewer novelties were detected among the main keywords used in recent barley documents, “crop rotation” and “fertilizer application” being the only innovative terms. This shows a much greater concern for the negative impact of environmental constraints on wheat crops and the prominence of wheat in the implementation of sustainable agroecosystem practices [24,26], which is in close correspondence with its larger cultivated area, higher production and socio-economic relevance compared to barley [50].
Our analysis also showed a higher number of terms related to genetic and molecular topics in the period 2000–2018 compared to the earlier period (21 versus 14 in “wheat” documents; 30 versus 24 in “barley” documents). The finding that, at any period, barley is connected with more keywords from this group than wheat is likely attributable to two different factors: (i) much more varied scientific topics have interested wheat researchers, which is reflected in the many keywords listed in the Scopus database that are related to other scientific disciplines; and (ii) molecular and reverse genetic approaches are more straight-forward in barley compared to wheat [48]. Our results have clearly demonstrated the different timelines of the progression of knowledge on wheat and barley in the affected disciplines (i.e., genetics and molecular biology). Up to 1999, most keywords in wheat mainly referred to molecules involved in genetic processes and their structure (Figure 9a). By contrast, “molecular cloning”, “mutation”, “gene expression” and “gene expression regulation” were already key terms in that earlier barley-related research (Figure 9b). It is significant that the keyword “molecular genetics” was found in a quite similar number of documents in the wheat and barley keyword lists (486 and 337, respectively) despite three-times more documents mentioned wheat than barley in that period (57,376 versus 21,060). In scientific documents published between 2000 and 2018, terms like “gene expression” and “gene expression regulation” have come to enter the wheat-related keywords list, which also includes, as remarkable novel terms, “chromosome mapping”, “genetic variability” and “genetic marker” among others (Figure 9c). Nevertheless, it seems again evident that the application of molecular tools has progressed much more quickly in barley, whose 2000-2018 list of main keywords includes, for instance, “quantitative trait loci” and “transgenic plant” (Figure 9d).
This idea is also supported by the number of documents related to genetics in absolute or relative terms for each crop. We evaluated the temporal distribution of the keyword “genetics” in wheat and barley publications. Results showed that both evolution lines followed similar patterns, although the number of genetics-related documents in wheat research increased more quickly than in barley from the year 2000 (Figure 9e). However, when these absolute numbers were relativized to the global volume of wheat and barley documents, the tendency lines changed. The ratio is higher for barley than for wheat since the 1980s, but especially from 2004 (Figure 9f). This again suggests that the use of reverse genetics is more common in barley than in wheat research. This is likely due to the fact that, although both species possess large genomes characterized by a high content of repetitive elements and large pericentromeric regions that are virtually devoid of meiotic recombination, the barley genome is diploid, while wheat varieties possess a tetra- or hexaploid genome. This has facilitated sequence of barley genome before the wheat genome (2012 versus 2018), giving barley a clear advantage over wheat for performing reverse genetics, analyzing the role of specific genes, and other numerous improvements [48].

3.4. Patents

The number of documents published on a specific research topic gives an idea about its scientific relevance. On the contrary, patent metrics allow to assess the industrial interest in that particular issue.
The temporal progressions of the number of patents related to wheat and barley have followed similar patterns (Figure 10a). Nevertheless, the counts for barley are always two to three times lower than for wheat, as already noted regarding scientific documents (see Figure 1). However, when the number of patents is weighted with respect to the number of documents published, a noticeable change is observed (Figure 10b). Until the 1970s, the ratio between the number of patents and documents was higher in wheat than in barley suggesting a higher scientific and industrial interest in wheat. From the 1970s to the beginning of the 21st century, the patent/scientific document ratio was similar in both crops, showing an increasing industrial interest in barley. Finally, in the last 10 years, the ratio for barley has at least doubled to that of wheat. This suggests that although the scientific community continues to maintain a greater focus on wheat, the industrial interest in barley has comparatively experienced a much higher relative increment (Figure 10b). The investment returns from innovations in malting procedures and novel beer brewing processes, including those involving the elaboration of trendy craft beers, are surely among the reasons encouraging the barley-related scientific community to protect the research outcomes suitable to be patented.

4. Conclusions

The bibliometric assessment of scientific documents related to wheat and barley has allowed us to analyse past and current trends in wheat and barley research. Some of the differences observed between the two sets of data can be explained by the distinct major human uses of wheat (human consumption) and barley (animal feeding and brewing), the former crop being much more represented in absolute terms (i.e., number of publications and patents) in the Scopus databases at any time analyzed. As expected because of their close botanical and agronomical relationship, wheat and barley research documents share many main keywords. However, some differences, mostly related to their respective uses by humans, different agricultural and economic prevalence and genome complexity, were found when keywords were grouped in thematic clusters. Our results point out the current importance of sustainability in agroecosystems for a major crop like wheat, and an increased focus of research projects on genetics and molecular biology in barley. The latter can be attributed to the diploid condition of barley, which has experienced an earlier and much faster development of genetic and genomic resources than wheat. Similarly, the evolution of the ratio of patents/scientific documents shows an increasing industrial interest in barley when compared to the temporal tendency of the protection of research results in wheat. Finally, the differences regarding document languages and top countries in the affiliations of publications dealing with wheat and barley seem attributable to some extent to the distinct socio-economic relevance of each of these crops on a global scale.

Author Contributions

F.M.-A. and E.G. conceived and designed the study; E.G. performed the bibliometric analysis; E.G., P.G. and E.B. analysed the data and wrote the paper.

Acknowledgments

This work was supported by the Spanish Ministry of Science, Innovation and Universities project AGL2016-77149 and the Comunidad de Madrid (Spain) project S2018/BAA-4330. The authors are grateful to the anonymous reviewers for their helpful comments and suggestions.

Conflicts of Interest

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

References

  1. Curtis, B.C. Wheat in the World. Available online: http://www.fao.org/3/y4011e/y4011e04.htm (accessed on 28 March 2019).
  2. Peña, R.J. Wheat for Bread and Other Foods. Available online: http://www.fao.org/3/y4011e/y4011e0w.htm (accessed on 28 March 2019).
  3. Shewry, P.R.; Hey, S.J. The contribution of wheat to human diet and health. Food Energy Secur. 2015, 4, 178–202. [Google Scholar] [CrossRef]
  4. Sarwar, M.H.; Sarwar, M.F.; Sarwar, M.; Qadri, N.A.; Moghal, S. The importance of cereals (Poaceae: Gramineae) nutrition in human health: A review. J. Cereals Oilseeds 2013, 4, 32–35. [Google Scholar] [CrossRef]
  5. Lafiandra, D.; Riccardi, G.; Shewry, P.R. Improving cereal grain carbohydrates for diet and health. J. Cereal Sci. 2014, 59, 312–326. [Google Scholar] [CrossRef] [PubMed]
  6. Selvendran, R.R.; Stevens, B.; Du Pont, M.S. Advances in food research. In Dietary Fiber: Chemistry, Analysis, and Properties; Elsevier: Amsterdam, The Netherlands, 1988; Volume 31, pp. 117–209. [Google Scholar] [CrossRef]
  7. EU Register of Nutrition and Health Claims Made on Foods. Available online: http://ec.europa.eu/nuhclaims/ (accessed on 28 March 2019).
  8. Healthgrain Project. Healthgrain Forum. Available online: https://healthgrain.org/healthgrain-project/ (accessed on 28 March 2019).
  9. Orth, R.A.; Shellenberger, J.A. Origin, production, and utilization of wheat. Wheat Chem. Technol. 1988, 3, 1–14. [Google Scholar] [CrossRef]
  10. Hoseney, R.C.; Rogers, D.E. The formation and properties of wheat flour doughs. Crit. Rev. Food Sci. Nutr. 1990, 29, 73–93. [Google Scholar] [CrossRef] [PubMed]
  11. Tye-Din, J.A.; Galipeau, H.; Agardh, D. Celiac disease: A review of current concepts in pathogenesis, prevention and novel therapies. Front. Pediatr. 2018, 6, 350. [Google Scholar] [CrossRef]
  12. Wendorf, F.; Schild, R.; El Hadidi, N.; Close, A.E.; Kobusiewicz, M.; Wieckowska, H.; Issawi, B.; Haas, H. Use of barley in the Egyptian late paleolithic. Science 1979, 205, 1341–1347. [Google Scholar] [CrossRef]
  13. Purugganan, M.D.; Fuller, D.Q. The nature of selection during plant domestication. Nature 2009, 457, 843–848. [Google Scholar] [CrossRef]
  14. Helbaek, H.; Hole, F.; Flannery, K.V.; Neely, J.A. Plant collecting, dry-farming, and irrigation agriculture in prehistoric Deh Luran. In Prehistory and Human Ecology of the Deh Luran Plain: An Early Village Sequence from Khuzistan; Hole, F., Flannery, K.V., Neely, J.A., Eds.; Memoirs of the Museum of Anthropology of the University of Michigan: Ann Arbor, MI, USA, 1969; pp. 383–426. [Google Scholar]
  15. Pourkheirandish, M.; Komatsuda, T. The importance of barley genetics and domestication in a global perspective. Ann. Bot. 2007, 100, 999–1008. [Google Scholar] [CrossRef]
  16. International Barley Hub. Available online: http://www.barleyhub.org/ (accessed on 28 March 2019).
  17. FAOSTAT. Food and Agriculture Organization of the United Nations. Available online: http://www.fao.org/faostat/en/ (accessed on 28 March 2019).
  18. Gürel, F.; Öztürk, Z.N.; Uçarlı, C.; Rosellini, D. Barley genes as tools to confer abiotic stress tolerance in crops. Front. Plant Sci. 2016, 7, 1137. [Google Scholar] [CrossRef]
  19. E-malt.com. Available online: http://e-malt.com/ (accessed on 28 March 2019).
  20. The Maltsters Association of Great Britain. Available online: http://www.ukmalt.com/malt-facts (accessed on 28 March 2019).
  21. Wheat Initiative. Available online: https://www.wheatinitiative.org/ (accessed on 28 March 2019).
  22. United Nations UN. Department of Economic and Social Affairs. Population Division. Available online: https://www.un.org/en/development/desa/population/index.asp (accessed on 28 March 2019).
  23. Lal, R. Climate change and global food security. In Climate Change, Soil Carbon Dynamics, and Global Food Security; CRC Press: Boca Raton, FL, USA, 2005; pp. 132–162. [Google Scholar]
  24. Roberts, D.; Mattoo, A. Sustainable agriculture—Enhancing environmental benefits, food nutritional quality and building crop resilience to abiotic and biotic stresses. Agriculture 2018, 8, 8. [Google Scholar] [CrossRef]
  25. Sanz-Cobeña, A.; Lassaletta, L.; Aguilera, E.; Del Prado, A.; Garnier, J.; Billen, G.; Iglesias, A.; Sanchez, B.; Guardia, G.; Abalos, D. Strategies for greenhouse gas emissions mitigation in Mediterranean agriculture: A review. Agric. Ecosyst. Environ. 2017, 238, 5–24. [Google Scholar] [CrossRef]
  26. Calabi-Floody, M.; Medina, J.; Rumpel, C.; Condron, L.M.; Hernandez, M.; Dumont, M.; de la Luz Mora, M. Smart Fertilizers as a strategy for sustainable agriculture. In Advances in agronomy; Elsevier: London, UK, 2018; Volume 147, pp. 119–157. [Google Scholar] [CrossRef]
  27. Cormier, F.; Foulkes, J.; Hirel, B.; Gouache, D.; Moënne-Loccoz, Y.; Le Gouis, J. Breeding for increased nitrogen-use efficiency: A review for wheat (T. aestivum L.). Plant Breed. 2016, 135, 255–278. [Google Scholar] [CrossRef]
  28. Kiba, T.; Krapp, A. Plant nitrogen acquisition under low availability: Regulation of uptake and root architecture. Plant Cell Physiol. 2016, 57, 707–714. [Google Scholar] [CrossRef]
  29. International Barley Genome Sequencing Consortium. A physical, genetic and functional sequence assembly of the barley genome. Nature 2012, 491, 711. [Google Scholar] [CrossRef]
  30. International Wheat Genome Sequencing Consortium. Shifting the limits in wheat research and breeding using a fully annotated reference genome. Science 2016, 361, eaar7191. [Google Scholar] [CrossRef]
  31. Bockelman, H.E.; Valkoun, J.; Ullrich, S.E. Barley germplasm conservation and resources. In Barley: Improvement, Production, and Uses; Wiley-Blackwell: Oxford, UK, 2010; pp. 144–159. [Google Scholar]
  32. Muñoz-Amatriaín, M.; Cuesta-Marcos, A.; Endelman, J.B.; Comadran, J.; Bonman, J.M.; Bockelman, H.E.; Chao, S.; Russell, J.; Waugh, R.; Hayes, P.M. The USDA barley core collection: Genetic diversity, population structure, and potential for genome-wide association studies. PLoS ONE 2014, 9, e94688. [Google Scholar] [CrossRef]
  33. Pixley, K.V.; Salinas-Garcia, G.E.; Hall, A.; Kropff, M.; Ortiz, C.; Bouvet, A.S.; Singh, S. CIMMYT’s Seeds of Discovery Initiative: Harnessing biodiversity for food security and sustainable development. Indian J. Plant Genet. Resour. 2017, 231–240. [Google Scholar] [CrossRef]
  34. Cañas-Guerrero, I.; Mazarrón, F.R.; Pou-Merina, A.; Calleja-Perucho, C.; Díaz-Rubio, G. Bibliometric analysis of research activity in the “Agronomy” category from the Web of Science, 1997–2011. Eur. J. Agron. 2013, 50, 19–28. [Google Scholar] [CrossRef]
  35. Singh, V.; Perdigones, A.; Garcia, J.L.; Cañas-Guerroro, I.; Mazarrón, F.R. Analyzing worldwide research in hardware architecture, 1997–2011. Commun. ACM 2015, 58, 76–85. [Google Scholar] [CrossRef]
  36. Rojas-Sola, J.I.; Aguilera-García, Á.I. Global Bibliometric Analysis of the ‘Mining & Mineral Processing’Subject Category from the Web of Science (1997–2012). Miner. Process. Extr. Metall. Rev. 2015, 36, 349–369. [Google Scholar] [CrossRef]
  37. Montoya, F.G.; Baños, R.; Meroño, J.E.; Manzano-Agugliaro, F. The research of water use in Spain. J. Clean. Prod. 2016, 112, 4719–4732. [Google Scholar] [CrossRef]
  38. De la Cruz-Lovera, C.; Perea-Moreno, A.; de la Cruz-Fernández, J.; Alvarez-Bermejo, J.; Manzano-Agugliaro, F. Worldwide research on energy efficiency and sustainability in public buildings. Sustainability 2017, 9, 1294. [Google Scholar] [CrossRef]
  39. Salmerón-Manzano, E.; Manzano-Agugliaro, F. Worldwide scientific production indexed by Scopus on Labour Relations. Publications 2017, 5, 25. [Google Scholar] [CrossRef]
  40. Archambault, É.; Campbell, D.; Gingras, Y.; Larivière, V. Comparing bibliometric statistics obtained from the Web of Science and Scopus. J. Am. Soc. Inf. Sci. Technol. 2009, 60, 1320–1326. [Google Scholar] [CrossRef]
  41. Mongeon, P.; Paul-Hus, A. The journal coverage of Web of Science and Scopus: A comparative analysis. Scientometrics 2016, 106, 213–228. [Google Scholar] [CrossRef]
  42. Montoya, F.G.; Alcayde, A.; Baños, R.; Manzano-Agugliaro, F. A fast method for identifying worldwide scientific collaborations using the Scopus database. Telemat. Inform. 2018, 35, 168–185. [Google Scholar] [CrossRef]
  43. Montoya, F.G.; Montoya, M.G.; Gómez, J.; Manzano-Agugliaro, F.; Alameda-Hernández, E. The research on energy in Spain: A scientometric approach. Renew. Sustain. Energy Rev. 2014, 173–183. [Google Scholar] [CrossRef]
  44. Fischbeck, G. Contribution of barley to agriculture: A brief overview. In Barley Science: Recent Advances from Molecular Biology to Agronomy of Yield and Quality; Food Products Press: New York, NY, USA, 2002; pp. 1–29. [Google Scholar]
  45. Gimenez, E.; Manzano-Agugliaro, F. DNA damage repair system in plants: A worldwide research update. Genes 2017, 8, 299. [Google Scholar] [CrossRef]
  46. Edwards, D.; Batley, J. Plant genome sequencing: Applications for crop improvement. Plant Biotechnol. J. 2010, 8, 2–9. [Google Scholar] [CrossRef]
  47. Shewry, P.R. Wheat. J. Exp. Bot. 2009, 60, 1537–1553. [Google Scholar] [CrossRef] [PubMed]
  48. Schulte, D.; Close, T.; Graner, A.; Langridge, P.; Matsumoto, T.; Muehlbauer, G.; Sato, K.; Schulma, A.H.; Waugh, R.; Stein, N. The international barley sequencing consortium—At the threshold of efficient access to the barley genome. Plant Physiol. 2009, 142–147. [Google Scholar] [CrossRef] [PubMed]
  49. Hicks, K.B.; Montanti, J.; Nghiem, N.P. Use of barley grain and straw for biofuels and other industrial uses. In Barley; Elsevier: Amsterdam, The Netherlands, 2014; pp. 269–291. [Google Scholar]
  50. Adams, R.M.; Hurd, B.H.; Lenhart, S.; Leary, N. Effects of global climate change on agriculture: An interpretative review. Clim. Res. 1998, 11, 19–30. [Google Scholar] [CrossRef]
Figure 1. Trends in publications on Wheat and Barley research fields.
Figure 1. Trends in publications on Wheat and Barley research fields.
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Figure 2. Worldwide research on wheat (a) and barley (b) up to 2018.
Figure 2. Worldwide research on wheat (a) and barley (b) up to 2018.
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Figure 3. Wheat (a,b) and barley (c,d) production by regions (a,c) and by countries (b,d). Source: FAOSTAT.
Figure 3. Wheat (a,b) and barley (c,d) production by regions (a,c) and by countries (b,d). Source: FAOSTAT.
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Figure 4. Languages of scientific output in the wheat and barley research fields.
Figure 4. Languages of scientific output in the wheat and barley research fields.
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Figure 5. Distribution (%) of worldwide research on wheat and barley by subject area, as classified by Scopus.
Figure 5. Distribution (%) of worldwide research on wheat and barley by subject area, as classified by Scopus.
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Figure 6. Word cloud based on the main keywords related to wheat (a) and barley (b) in worldwide research.
Figure 6. Word cloud based on the main keywords related to wheat (a) and barley (b) in worldwide research.
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Figure 7. Word cloud based on the main keywords related to cereals and model plants (a,b), and human and animals (c,d), in wheat (a,c) and barley (b,d) research documents.
Figure 7. Word cloud based on the main keywords related to cereals and model plants (a,b), and human and animals (c,d), in wheat (a,c) and barley (b,d) research documents.
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Figure 8. (ad) Word cloud based on the main keywords related to agronomy in worldwide research until 1999 (a,b) and from 2000 (c,d) in wheat (a,c) and barley (b,d).
Figure 8. (ad) Word cloud based on the main keywords related to agronomy in worldwide research until 1999 (a,b) and from 2000 (c,d) in wheat (a,c) and barley (b,d).
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Figure 9. (ad) Word cloud based on the main keywords related to genes and proteins in wheat (a,c) and barley (b,d) in worldwide research until (a,b) and from (c,d) the year 2000. (e) Number of genetics-related documents by year in the wheat and barley research fields. (f) Number of genetics-related documents with respect to the total number of scientific document in the wheat and barley research fields.
Figure 9. (ad) Word cloud based on the main keywords related to genes and proteins in wheat (a,c) and barley (b,d) in worldwide research until (a,b) and from (c,d) the year 2000. (e) Number of genetics-related documents by year in the wheat and barley research fields. (f) Number of genetics-related documents with respect to the total number of scientific document in the wheat and barley research fields.
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Figure 10. Trends in patents in the wheat and barley research fields. (a) Number of patents by year. (b) Ratio between patents and scientific documents.
Figure 10. Trends in patents in the wheat and barley research fields. (a) Number of patents by year. (b) Ratio between patents and scientific documents.
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Table 1. Scientific production by countries measured by the absolute number (N) and the relative contribution (%) of documents in the wheat and barley research fields. Their position in a ranking according to number of documents published is also indicated.
Table 1. Scientific production by countries measured by the absolute number (N) and the relative contribution (%) of documents in the wheat and barley research fields. Their position in a ranking according to number of documents published is also indicated.
WheatBarley
PositionCOUNTRYN%PositionCOUNTRYN%
1United States3189915.401United States764612.20
2China2188810.572United Kingdom664610.60
3India128456.203Germany42626.80
4United Kingdom120755.834Canada40606.48
5Australia107375.185Australia33465.34
6Canada89134.306Japan27794.43
7Germany87464.227China23733.78
8Japan78083.778Denmark23333.72
9France63983.099Spain19923.18
10Italy52922.5610India15002.39
11Spain41021.9811Sweden14852.37
12Pakistan34751.6812Italy13412.14
13Iran34051.6413France13032.08
14Brazil31421.5214Poland12672.02
15Poland31351.5115Iran9931.58
16Turkey29271.4116Finland9671.54
17Netherlands28811.3917Czech Republic9571.53
18Russian Federation28381.3718Netherlands9031.44
19Sweden25761.2419Russian Federation8461.35
20Mexico22581.0920Turkey7441.19
21Denmark22581.0421South Korea7111.13
26Czech Republic16600.8028Brazil4510.72
29South Korea14210.6935Mexico3130.50
30Finland13030.6338Pakistan2590.41
Table 2. Rankings of the 20 most productive institutions in the wheat and barley research fields. Institutions included in both lists are in bold lettering.
Table 2. Rankings of the 20 most productive institutions in the wheat and barley research fields. Institutions included in both lists are in bold lettering.
WheatBarley
AffiliationCountryNAffiliationCountryN
USDA Agricultural Research Service, Washington DC *USA4798Agriculture et Agroalimentaire Canada *Canada1695
Chinese Academy of SciencesChina4107USDA Agricultural Research Service, Washington DC *USA1184
Agriculture et Agroalimentaire Canada *Canada3355United States Department of Agriculture *USA794
United States Department of Agriculture *USA3260Sveriges lantbruksuniversitet *Sweden754
INRA Institut National de La Recherche Agronomique *France3152Rothamsted Research *UK739
Chinese Academy of Agricultural Sciences *China2231Leibniz Institute of Plant Genetics and Crop Plant Research *Germany705
Kansas State UniversityUSA2129The University of AdelaideAustralia678
China Agricultural University *China2088University of SaskatchewanCanada628
Northwest A&F University *China1764The James Hutton Institute *Scotland621
Rothamsted Research *UK1750University of AlbertaCanada602
Indian Agricultural Research Institute *India1708INRA Institut National de La Recherche Agronomique *France592
Wageningen University and Research Centre *Netherlands1564Danmarks Tekniske UniversitetDenmark573
Ministry of Agriculture of the People’s Republic of China *China1497Wageningen University and Research Centre *Netherlands531
CSIRO Plant Industry *Australia1367Carlsberg Research CenterDenmark527
Washington State University PullmanUSA1334University of Copenhagen Faculty of Life Sciences *Denmark484
Ministry of Education, ChinaChina1292Københavns UniversitetDenmark481
The University of AdelaideAustralia1274Washington State University PullmanUSA465
Punjab Agricultural University, India *India1251CSIRO Plant Industry *Australia458
Nanjing Agricultural University *China1235University of California, DavisUSA401
University of SaskatchewanCanada1208University of ManitobaCanada389
* Research Institutions focused on Agronomy. N: Number of scientific documents published by affiliation.
Table 3. Top 10 sources of publications in the wheat and barley research fields. Journals included in both lists are in bold lettering.
Table 3. Top 10 sources of publications in the wheat and barley research fields. Journals included in both lists are in bold lettering.
WheatBarley
Source Title *NSource TitleN
Theoretical And Applied Genetics (2)2048Journal Of The Institute Of Brewing897
Journal Of Cereal Science (15)1762Theoretical And Applied Genetics771
Journal Of Agricultural And Food Chemistry (12)1734Animal Feed Science And Technology669
Euphytica (9)1715Plant Physiology577
Plant And Soil (7)1370Journal Of Agricultural Science564
Cereal Research Communications (36)1303Journal Of Experimental Botany561
Cereal Chemistry (43)1273Plant And Soil540
Journal Of The Science Of Food And Agriculture (11)1249Planta517
Field Crops Research (45)1212Euphytica501
Crop Science (25)1209Physiologia Plantarum476
* Numbers in brackets indicate the journal position in the barley list. N: Number of scientific document published in each source.
Table 4. Distribution of document types for research on wheat and barley.
Table 4. Distribution of document types for research on wheat and barley.
WheatBarley
DOCUMENT TYPEN *%N%
Article15191489.734569591.13
Conference Paper72294.2713872.77
Review43882.5914662.92
Book Chapter22541.337451.49
Book1900.11500.10
Conference Review1740.10180.04
Others31481.867791.55
* N: Number of scientific documents in each category. %: percentage of documents published in each category.
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