Introductory Chapter: World Citrus Production and Research

1. Introduction

The set of plants producing citrus fruits is composed of a large number of species from the Citrus, Fortunella, and Poncirus genera. Among the main species are sweet oranges (Citrus sinensis) and bitter oranges (Citrus aurantium), mandarins (e.g. Citrus reticulata, Citrus delicia, Citrus clementina, Citrus unshiu, and Citrus nobilis), lemons (Citrus limon), limes (e.g. Citrus latifolia, Citrus aurantifolia and Citrus limettioides), grapefruits (Citrus paradisi), pummelos (Citrus maxima), kumquats (Fortunella spp.), and trifoliate orange (Poncirus trifoliata). Fruits of commercial importance for human consumption are mainly from Citrus species. In a small proportion, Fortunella species (fruits known as kumquats) are also worthed. Moreover, several hybrids such as tangors (mandarin × sweet orange) and tangelos (mandarin × grapefruit) are also important commercially. On the other hand, P. trifoliata and its hybrids Citrus spp. are used only as rootstocks, not being edible [1].

2. World production

Among the main fruits produced in the world, citrus are highlighted. The citrus fruits were the second most produced fruit worldwide in 2021, accounting for 161.8 million tons produced in more than 10.2 million hectares. Only bananas and plantains combined exceeded this amount, reaching more than 170.3 million tons [2].

Oranges world production is the most significant within citrus, reaching 75.57 million tons (46.7% of citrus fruit production) in a harvested area of 9.93 million hectares. The second most important fruits are tangerines, with a production of 41.95 million tons (25.9% of citrus fruit production) in a harvested area of 3.11 million hectares. Otherwise, limes and lemons reached 20.83 million tones (12.87% of citrus fruit production) in a harvested area of 1.34 million hectares. Besides, pomelos and grapefruits (C. paradisi and C. máxima) and other fruits (Citrus medica, Citrus bergamia, Citrus myrtifolia and Fortunella spp.) are also notorious. Pomelos and grapefruits have a production of 9.56 million tons while other citrus fruits have a production of 13.90 million tons (Figure 1) [2].

Figure 1.

World production of different citrus fruits between 1961 and 2021 [2].

Among the largest producing countries, China, Brazil, and India can be highlighted. The great productivity of Chine is mainly due to the larger production of tangerines and other citrus fruits. As for Brazil, it is the largest producer of oranges and the largest exporter of orange juice. In turn, India is the world’s largest producer of lemons and limes. Additionally, Mexico, Spain, United States of America, Türkiye, Egypt, Nigeria, and Iran must also be noted as the top 10 producers of citrus fruits in 2021 [2].

Also, world production of citrus has increased almost 5.5 times in the last 60 years. Notably, in the last 10 years (between 2021 and 2011), there was the highest increase to tangerines production, with more than 1.44 million tons produced per year. In turn, oranges production increased by 312 thousand tones per year while the lemons and limes one increased by 578 thousand tons per year (Figure 1) [2].

3. Research on citrus

Scientific production about citrus is equally important in different areas of human knowledge. From the search for the term “citrus” in the “all fields” option in the Scopus and Web of Science databases in the last 5 years (2018–2022), there was an increasing number of publications in both databases [3, 4]. Although the search with the term “all fields” retrieves in very broad number of publications, the Scopus database included a much larger number of publications. In year of 2022, from Scopus database were retrieved 31,103 documents while for Web of Science database a lower number was recovered (2,839 publications) (Figure 2A).

Figure 2.

(A) Number of publications retrieved from Scopus and Web of Science databases searching for the term “citrus” in all fields (ALL(citrus); (B) Most relevant countries when searching for term “citrus” in “article title, abstract and keywords” (TITLE-ABS-KEY(citrus)) in Scopus database; (C) Main knowledge subject areas when term “citrus” was search in article title, abstract and keywords (TITLE-ABS-KEY(citrus)). The searches were performed in the last 5 years (2018 to 2022).

Then, a new, more restrictive search was performed in Scopus database, from 2018 to 2022 searching the term “citrus” in the “article title, abstract, and keywords” option. A total of 21,954 results were retrieved, where 66% of these publications are from the last three years (from 2020 to 2022). Therefore, citrus research is a topic of current relevance (Figure 2A).

Regarding to the countries that most contributed to publications about citrus in the last 5 years, there are China, United States, India, Brazil, Spain, Italy, Iran, South Korea, Japan, and Pakistan. Of these, six were also the top 10 citrus fruit producers in 2021, namely: China, Brazil, India, Spain, United States, and Iran [1]. China is the biggest contributor, with 28.66% of the total published. Researchers from USA and India have published more than 2,000 articles, standing for 11.82% and 10.12% of the total articles produced in the period, respectively. Further, with more than 1,000 publications are Brazil, Spain, and Italy. Besides, Iran, South Korea, Japan, and Pakistan had around 600–1,000 publications. Additionally, the great importance of Asian countries to knowledge production related to “citrus” can be noted as they account for more than 50% of total publications (Figure 2B) [3].

As to the subject areas by Scopus database classification, 43.4% of the publications were from Agricultural and Biological Sciences. The second most important area was Chemistry (19.6%), followed by Biochemistry, Genetics and Molecular Sciences (17.9%). Also, there was a significant number of publications addressing citrus in other areas of knowledge: Environmental Science, Material Science, Engineering, Chemical Engineering. Yet, some part of publications was applied to the medical and pharmacological area (Figure 2C).

Furthermore, many patents are report on citrus. In a search in the Derwent Innovations patent database over the last 5 years (2018–2022) [5], using the term “citrus” as a topic resulted in 6977 patents. The majority of these publications cover the following areas: chemistry, agriculture, biotechnology, instruments, food science, pharmacology. Hence, research on citrus is directed to several areas of knowledge, which shows its importance and the need of continuous increase in its knowledge.