Bibliometric analysis of strawberry ( Fragaria × ananassa Duch.) research publications from horticulture category based on Web of Science

2.1 Web of Science

Clarivate Analytics’s Web of Science (WoS) is the world’s leading scientific citation search and analytical information platform, and the one of the world’s largest and most comprehensive academic information resources covering more than 12,000 core academic journals. The publication counts from the Web of Science Core Collection were derived from the following databases: The Science Citation Index—Expanded (SCIE)–1900-present, Social Science Citation Index (SSCI) –1900-present, Conference Proceeding Citation Index-Science (CPCI-S) –2015-present, Conference Proceedings Citation Index- Social Science & Humanities (CPCI-SSH) –2015-present, Current Chemical Reactions (CCR-EXPANDED) –1985-present, Index Chemicus (IC) –1993-present.

2.2 Data collection and analysis

This study surveyed papers in WoS Core Collection (1900-present) (retrieval data last updated: 2021-3-16). We used the keywords in the topic, with the query

Topic: (Strawberry OR “Fragaria ananassa Duch.”)

Then refined by: Document Types: (Article or Review) and WoS Categories: (Horticulture).

There are 2,640 papers from WoS Core Collection. Full record and cited references of the included papers were extracted at other reference software file format and imported into VOSviewer (version 1.6.16, 2020, Leiden University, Leiden, The Netherlands) for further citation analysis. The impact factors (IF 2019 and IF 5 year) were taken from the Journal Citation Report (JCR 2019) published in 2020, which had the latest data available.

2.3 VOSviewer

Visualizations (network and overlay) using program VOSviewer are conducted on WOS data in order to determine co-occurrence and clusters of connected publications, country input and author collaboration (co-authorship) as well as clusters of interrelated research topics (text data). In this work, we used VOSviewer to show the international collaboration between the authors, organizations, countries and the research trends through all keywords [32]. In this paper, default parameters values of the VOSviewer are usually used in the analysis. Items are represented by a label and a circle. The size of circles reflects the weight of an item. Some items are not displayed in avoidance of overlapping. The colors in network visualization (text maps) represent clusters of similar items as calculated by the program. Distance between the items indicates the strength of relationships.

3.1 Document type and language of publication

Based on Clarivate Analytics’s WoS Index, the 2,640 papers were SCIE (2,640), CPCI-S (45) and SSCI (6).

The paper document types and languages were displayed in the Table 1. Among the document types, there are articles (2,603, 98.598 %) and reviews (37, 1.402 %), also including proceedings papers (45, 1.705 %) and Early Access (3, 0.114 %). The first paper titled of “Ascorbic acid content of strawberry varieties and selections at geneva, new-york in 1945” wrote by Slate and Robinson (1946) was published in Proceedings of the American Society for Horticultural Science (47 : 219-223) [33].

All of the papers were almost published in English (2,426, 91.894 %), and then others were Korean (68, 2.576 %), Japanese (49, 1.856 %), Portuguese (47, 1.78 %), German (35, 1.326 %), Spanish (8, 0.303 %), French (4, 0.152 %), and Chinese (3, 0.114 %), etc. The English was dominating language from the WoS, and scholars tend to publish their articles in English as they want them to be widely accepted. Most of the published documents were in the form of original research articles and English was the most common language used [34].

With the aim of knowing the research trend in strawberry research from Horticulture category based on WoS, a total number of 2,640 article and review publications trend was obtained from the online version of WoS database from 1946 to 2021 (Fig. 1). The highest number of papers (169) were published in 2019. In general, the quantity of strawberry research literature presents a fast growth tendency. The ratio of the publications after 1980, 1990, 2000 and 2010 till 2021 were 91.44 %, 82.765 %, 68.789 %and 46.705 %, respectively. The h-index was initially proposed as a measure of a researcher’s scientific output based on counting the number of publications (N) by that researcher cited N or more times [35]. For the total 2, 640 papers, the h-index is 78, and the average citation per item is 15.4.

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Fig. 1

Number of published papers of Strawberry research from Horticulture category based on Web of Science from 1946 to 2021.

For Strawberry research from Horticulture category based on WoS, there are total ten WoS subject categories in the science edition (total 254 categories) and nine research areas. Table 2 shows the all WoS Categories and research areas in the subject of Strawberry research from Horticulture category based on WoS. The top five WoS Categories include Horticulture (2,640, 100 %), Agronomy (581, 22.008 %), Plant Sciences (372, 14.091 %), Food Science Technology (356, 13.485 %), and Genetics Heredity (102, 3.864 %). The top five research areas include Agriculture (2,640, 100 %), Plant Sciences (372, 14.091 %), Food Science Technology (356, 13.485 %), Genetics Heredity (102, 3.864 %), and Nutrition Dietetics (64, 2.424 %). The journals or papers may be classified in two or more categories in the WoS, shows the multidisciplinary character of this research field [36, 37]. Documents are mapped to one or several research areas in WoS. Areas are assigned to publications and then mapped to each document (paper) in a publication. Therefore, publications can be mapped to several different areas. In WoS, publications are also mapped to WoS categories which are more detailed than areas [38].

Based on JCR 2019 data (published in 2020), there are 57 Journals and one book series for Strawberry research from Horticulture category based on WoS. Among these, the one book series is ACS Symposium Series (1). The top 20 core journals were displayed in the Table 3 with total articles each more than 38 papers, Journal impact factor as IF 2019 and IF 5 year, rank and Quartile in Category.

The top 5 Journals, top 10, top 15 and top 20 Journals published about 49.242 %, 66.591 %, 76.932 %and 84.545 %of the total papers, respectively. The top five Journals are Hortscience (360, 13.636 %), Scientia Horticulturae (322, 12.197 %), Journal of the American Society for Horticultural Science (248, 9.394 %), Postharvest Biology and Technology (236, 8.939 %), and Journal of Horticultural Science Biotechnology (134, 5.076 %), each published more than 134 papers. In general, we combined the current and formerly Journal title as one (Table 3), but the total number of Journals in the WoS were calculated separately. Based on results of Table 3, among the top 20 journals, three journals are in Quartile 1, seven journals in Quartile 2, four journals in Quartile 3, three journals in Quartile 4 in Category. White-Gibson et al. (2019) have also demonstrated the importance of publishing in the English language and in a journal with a high impact factor. Citation analysis is not a measurement of scientific quality, but it is reflective of the importance [39].

According to the publication data in the citation of 57 journals, there were 44 journals meet the thresholds of 5 publications. The network of citation in the field of Strawberry research from Horticulture category based on WoS is shown seven clusters with different colors in Fig. 2, the size of circles reflects a total number of journal publication records. The seven cluster colors from 1 to 7 are red, green, blue, yellow, violet, shallow blue and orange. Journals in the same cluster usually suggested that they published the similar content papers and had close relations with each other.

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Fig. 2

Network visualization maps of citation journals in Strawberry research from Horticulture category based on Web of Science with 44 nodes and 7 clusters.

In general, internationally collaborative articles had the highest visibility and scientific impact followed by inter-institutional collaborative articles, single-country articles and single-author articles, respectively [40]. According to the publication data, it was revealed that a total of 6,807 authors published 2,640 publications, there were 233 authors meet the thresholds of 5 publications, but only 52 authors were connected to each other. The network of authorship in the field of Network visualization maps of authors of Strawberry research from Horticulture category based on WoS is shown in Fig. 3, the size of circles reflects a total number of records. Authors in the same cluster usually suggested that they studied in a similar field and had close cooperation with each other.

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Fig. 3

Network visualization maps of authors of Strawberry research from Horticulture category based on Web of Science.

Table 4 provided the top 19 authors published more than 16 papers, and also lay the citations, average citations, organization-enhenced and Countries. Though we combined the same author with the different spell, but the total number of authors were calculated separately. Top 5 authors are Hancock, James F. (Hancock, JF); Shaw, DV; Chandler, Craig K. (Chandler, CK); Whitaker, Vance M.; Choi, Jong Myung, each published more than 28 papers. Top 5 authors with higher citations per paper are Breen, PJ; Simpson, D.W. (Simpson, DW); Maas, JL; Galletta, GJ; Sonsteby, Anita (Sonsteby, A.), average citations per paper are more than 22.39 times. The top 19 authors are mainly from USA. There are 12 authors from USA, South Korea and Japan are each with 2 authors, Norway, England and Germany are each with 1 author.

There are 77 countries or regions contributing the 2,640 papers in this study. Table 5 represent the lists of the top 20 countries/regions that the published more than 29 papers, and also show the cluster, total link strength, citations and average citations. Among 20 countries, USA, Peoples R China, Japan, South Korea, Brazil are the five most papers country. In case of the average citations, France, Spain, Argentina, New Zealand and England show the higher citations per paper.

We developed the international country co-authorship network map using VOSviewer software (Fig. 4). There are 48 countries/regions that met the requirement threshold as five, and connected to each other. The VOSviewer software divided these 48 countries/regions into 10 clusters with different colors, the size of circles reflects a total number of records and the distance between the countries indicates the strength of relationships. The different colors group, the different clusters formed by sets of countries. Distance between the countries indicates the strength of relationships.

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Fig. 4

The country co-authorship network of Strawberry research from Horticulture category based on Web of Science with 48 nodes and 10 clusters.

According to Fig. 4, the first cluster consisted of 8 countries and regions (red color), Germany, Denmark, Serbia, Austria, Switzerland, Croatia, Romania, Slovenia. The second cluster consisted of 7 countries or regions (green color), Italy, Turkey, Iran, Norway, Greece, Finland, Hungary. The third cluster consisted of 6 countries (blue color), India, Australia, Scotland, Israel, Thailand, South Africa. The fourth cluster consisted of 5 countries and regions (yellow color), Japan, South Korea, Bangladesh, Sweden, Vietnam. The fifth cluster consisted of 5 countries (violet), Brazil, Spain, France, Portugal, Ireland. The sixth cluster consisted of 5 countries (shallow blue), Canada, New Zealand, Netherlands, Belgium, Czech Republic. The seventh cluster consisted of 4 countries (orange), England, Mexico, Pakistan, Tunisia. The eighth cluster consisted of 4 countries and regions (crown), USA, Argentina, Chile, Taiwan. The ninth cluster consisted of 2 countries (pink) of Poland and Estonia. The tenth cluster consisted of 2 countries of Peoples R China and Egypt. More cooperation could bring more advanced achievements in scientific research. Therefore, geographical location is an important factor that determines international cooperation. Nowadays, increasing international exchanges have promoted academic communications [41].

According to the publication data, it was revealed that a total of 1,504 organizations published 2,640 publications. Organization co-authorship analysis reflects the degree of communication between institutions as well as the influential institutions in this field [42]. Table 6 represents the top 20 organizations and institutions that the publications were above 19 papers ranked by the number of total publications, and also show the total link strength, citations, average citations and country. We combined the same organization with the different spell, but the total organization numbers in the WoS were calculated by separately. These organizations are mainly focused in USA with 10 organizations; South Korea with 4 organizations; China with 3 organizations; Canada with 2 organizations; and Univ Talca of Chile. Univ Florida, Univ Calif Davis, USDA ARS, ARS, Michigan State Univ are the five most paper organizations. The organizations of Oregon State Univ, Univ Calif Davis, Zhejiang Univ, Cornell Univ and Univ Talca show the higher average citations.

Among the total 1,504 organizations, there were 165 organizations met the minimum thresholds of five, but 139 organizations connected to each other (Fig. 5). The VOSviewer software divided these 139 institutes into 15 clusters with different colors. Within the context of network formation, organizations tend to form bonds with other institutions in the same region. Geographical localization is an important factor for partnership and joint venture. Therefore, there is a heavy presence of intra-institutional relationships within the scientific network on publications.

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Fig. 5

The organizations co-authorship network of Strawberry research from Horticulture category based on Web of Science.

Figure 6 shows the network map that links the all keywords to the entire sample of the articles analyzed. Among the all 7,332 keywords, only 753 keywords met the threshold level of more than five times included in the map. There are eight main clusters that represent different viewpoints on Strawberry (Fragaria×ananassa Duch.) research from Horticulture category based on WoS. The top twenty co-occurrence keywords were strawberry, fragaria x ananassa, quality, growth, cultivars, yield, fragaria x ananassa, fruit, temperature, plants, storage, identification, strawberry fruit, strawberries, resistance, fragaria, expression, photoperiod, anthocyanins, fruit quality, etc.

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Fig. 6

VOSviewer co-occurrence Network visualization mapping of most frequent all keywords (minimum of 5 occurrences) in Strawberry research from Horticulture category based on Web of Science.

The same data were then arranged by a period of Strawberry (Fragaria×ananassa Duch.) research as overlay map (Fig. 7). Blue colors indicate earlier research topics, whereas, yellow and green colors indicate more recent topics of interest. The blue colored topics do not indicate no longer research work on that topics. It usually indicates that, on average, this topic was intensely investigated earlier and now more attention has shifted towards other topics.

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Fig. 7

VOSviewer co-occurrence overlay visualization mapping of most frequent all keywords (minimum of 5 occurrences) in Strawberry research from Horticulture category based on Web of Science.

The top 20 keywords were list and ranked in each cluster (Fig. 6).

The first cluster (Red) is focused on plants growth and fruit-quality, including keyword terms as growth, plants, leaves, photosynthesis, fruit-quality, responses, apple, stress, nitrogen, plant-growth, tolerance, micropropagation, propagation, calcium, salinity, water, fragaria-chiloensis, greenhouse, regeneration, induction, etc.

The second cluster (Green) represents the strawberry diseases and biocontrol management, keyword terms ranked as fragaria x ananassa, resistance, botrytis-cinerea, botrytis cinerea, anthracnose, management, infection, soil, fragaria ananassa, gray mold, fruit breeding, biological-control, chloropicrin, rot, in-vitro, methyl bromide, disease, diseases, pathogens, methyl-bromide, etc.

The third cluster (blue) is focused on strawberries fruit quality changes during storage, including keyword terms as quality, fruit, storage, strawberries, ethylene, shelf-life, firmness, decay, postharvest, vegetables, flavor, aroma, chitosan, shelf life, atmospheres, cold-storage, life, respiration, ananassa, ascorbic-acid, etc.

The fourth cluster (yellow) represents strawberry breeding and identification, keyword terms ranked as fragaria x ananassa, identification, fragaria, inheritance, disease resistance, linkage map, diversity, selection, breeding, fragaria-x-ananassa, genetic diversity, genome, genotypes, heritability, peach, traits, rosaceae, microsatellite markers, germplasm, etc.

The fifth cluster (violet) is focused on cultivars methods affecting fruit yield and quality, including keyword terms as cultivars, yield, temperature, photoperiod, fruit quality, light, fragaria x ananassa duch., performance, fruit yield, flowering, system, vegetative growth, field, productivity, irrigation, plasticulture, flower, junebearing, plastic mulch, fruit production, etc.

The sixth cluster (shallow blue) is focused on fruit anthocyanins and antioxidant capacity, keyword terms ranked as anthocyanins, antioxidant capacity, fruits, antioxidant activity, phenolics, anthocyanin, phenolic-compounds, acid, color, capacity, cultivar, antioxidant, vitamin-c, berries, flavonoids, fragaria x ananassa duch, ascorbic acid, phenolic compounds, sugars, acids, et al.

The seventh cluster (orange) is focused on strawberry fruit biosynthesis and gene-expression, keyword terms as strawberry, strawberry fruit, expression, metabolism, tomato, biosynthesis, accumulation, gene, gene-expression, tomato fruit, Arabidopsis, ripening, arabidopsis-thaliana, plant, enzymes, genes, softening, gene expression, protein, abscisic-acid, etc.

The eighth cluster (brown) is focused on physiological and biochemical reaction to stress, keyword terms as phenylalanine ammonia-lyase, salicylic-acid, antioxidant enzymes, oxidative stress, hydrogen-peroxide, induced resistance, methyl jasmonate, peroxidase, radiation, polyphenol oxidase, irradiation, salt stress, superoxide-dismutase, damage, UV-c, ethylene production, lipid-peroxidation, antioxidant enzyme, ascorbate, cell-wall, etc.

Top papers are the sum of hot papers and highly cited papers, based on Clarivate Analytics’ Essential Science Indicators (ESI). Highly cited paper is a paper that belongs to the top 1%of papers in a research field published in a specified year. The 1 %is determined by the highly cited threshold calculated for the research field in the specified year. Hot paper is a paper published in the past two years that received a number of citations in the most recent two-month period that places it in the top 0.1%of papers in the same field. Here, the Essential Science Indicators database covers over a 10-year and 10-month period: January 1, 2010 - October 31, 2020.

Based on ESI database, these top papers are six highly cited papers, with one hot paper (Table 7). These six top papers are all published in Postharvest Biology and Technology. The paper wrote by Yan et al. (2019) are both highly cited papers and hot paper [47].

Citation analysis has been employed as a supplementary index to determine the impact of scientific studies, and to identify studies, researchers and the most renowned institutions dealing with the theme. Although a great many articles have been published, a relatively small number of individuals account for a large proportion of the citations within the period. Here, the total citations for the most eight frequently cited articles are more than 203 times, which authors were Cheng and Breen (1991), Dirlewanger et al. (2002), Han et al. (2004), Hazarika (2006), Assis et al. (2001), Ribeiro et al. (2007), Pesis (2005), and Gorny et al. (2002) in Figure 8 [49–56]. It can be found that the citation per year of the papers increased till to 2020, but the increase rate is different. The citations per year is still increased for the paper (blue line) published in Journal of the American Society for Horticultural Science and wrote by Cheng and Breen (1991) [49], and the average citations per year is the highest value as 22.3 (red line) in the 8 papers. The number of citations to a paper is considered a good quantitative measure of a paper’s impact.

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Fig. 8

Comparison of the citations per year of the most eight papers from their initial publications to March 16, 2021.