Barbados to its development as an im- Grapefruit: History, Use, and Breeding portant agricultural commodity. We review the progress and fluctuations Eliezer S. Louzada1 and Chandrika Ramadugu2 in production and market aspects. Be- cause grapefruit is valued as a highly nutritious fruit, we will discuss the sig- ADDITIONAL INDEX WORDS. biotechnology, drug interaction, mutation breeding, nificant health benefits associated with natural mutation, protoplast, somatic hybrids it. Interaction of grapefruit with cer- SUMMARY. Grapefruit [Citrus 3aurantium (synonym C. 3paradisi)] is an tain commonly used drugs has been important citrus commodity that originated in Barbados in the 17th century. reported; we examine the mode of in- Citrus Grapefruit is the youngest member of the genus . Most commercially teractions and address this concern. important grapefruit cultivars arose through natural and induced mutations, not The first commercial cultivation traditional breeding, of the white-fleshed and seedy Duncan grapefruit. Now, cultivars with a range of flesh colors exist; the pigmentation is correlated with of grapefruit occurred less than 200 lycopene content. A bud sport mutant of grapefruit discovered in Texas has a years ago. The original grapefruit tree deep golden-colored flesh, significantly different from the typical reddish produced very seedy fruit with white pigmentation. In this review, we discuss grapefruit’s journey from its origin in flesh; however, today, several different Barbados and its global establishment including production, marketing, drug cultivars of nearly seedless fruit with a interactions, cultivar development, genetic diversity, and commercially significant range of flesh coloration are available. cultivars. We review the advances in grapefruit cultivar development, the efforts to- ward breeding novel, potentially de- sirable cultivars through conventional  (Citrus maxima), describing it as a rapefruit (Citrus aurantium) breeding, induction of mutations “smaller shaddock.” Macfadyen (1830) belongs to the family Ruta- through irradiations, and other bio- classified the “forbidden fruit” reported Gceae, subfamily Aurantioideae. technological approaches that may be by both Browne and Hughes as Citrus Grapefruit is unique among citrus useful for cultivar improvement. Fi- Âparadisi also known as “barbados (Citrus sp.) fruit due to its distinctive nally, we describe the most important fl fi grapefruit.” Bowman and Gmitter avor, health bene ts, and recent Ca- commercial grapefruit cultivars. ribbean islands’ origin less than 300 (1990) and Gmitter (1995) further con- years ago (Scora, 1975). Most cultivat- firmed the association of the now ex- Commercial importance and tinct “forbidden fruit” with ‘Shaddock’ ed citrus originated in Southeast Asia market history before 2000 BCE. Citron (Citrus med- pummelo and the present-day grape- ica), considered a progenitor species of fruit. Based on chemotaxonomy (Scora THE UNITED STATES LEADS THE et al., 1982) and molecular data (Wu GRAPEFRUIT MARKET. Grapefruit was cultivated citrus (Raveh et al., 2020), fi dates back to 4000 BCE (Webber, et al., 2018), it is presumed that an acci- con ned to the Caribbean islands for 1967). dental hybridization produced the inter- several hundred years. Zoller (1918) fi fl The origin of grapefruit in the speci c hybrid of a pummelo and sweet reported grapefruit ourishing in  Caribbean islands is shrouded in mys- orange [C. aurantium var. sinensis Mexico for decades before Count  fi tery and confusion (Kumamoto et al., (synonym C. sinensis)], now classi ed Odette Philippe brought grapefruit 1987). Hughes (1750) reported a as grapefruit. Earlier, grapefruit was con- seeds to Florida in 1823, raised trees, tree bearing the “forbidden fruit” in sidered an apomictically stabilized hy- and distributed seeds freely (Robin- Barbados, but today’s grapefruit is brid species (Kumamoto et al., 1987). son, 1952). Regardless of the source not a direct descendent of this tree. However, taxonomists now charac- of early grapefruit germplasm, it was Browne (1756) also reported a tree terize grapefruit as a set of cultivars in the United States that grapefruit fi fi bearing the “forbidden fruit” and as- rather than a species; it is classi ed rst gained commercial importance.  sociated it with ‘Shaddock’ pummelo as C. aurantium (M. Schori, per- Initially there was confusion about sonal communication). grapefruit’s nomenclature. Commer- ’ Received for publication 29 June. 2020. Accepted for This review discusses grapefruit s cially it was known as grapefruit publication 12 Mar. 2021. evolution from its identification in (Humes, 1909), and “pomelo” was a Published online 5 May 2021. 1Texas A&M University Kingsville, Citrus Center, 312 N. International Blvd, Weslaco, TX 78599 Units 2Department of Botany and Plant Sciences, Univer- To convert U.S. to SI, To convert SI to U.S., sity of California Riverside, 900 University Avenue, multiply by U.S. unit SI unit multiply by Riverside, CA 92521 0.4047 acre(s) ha 2.4711 We thank Melanie Schori of the U.S. Department 4.1868 calorie(s) kJ 0.2388 of Agriculture, Agricultural Research Service, for 3.7854 gal L 0.2642 help with the recent taxonomic names of citrus 2.54 inch(es) cm 0.3937 cultivars. 0.4536 lb kg 2.2046 E.S.L. is the corresponding author. E-mail: Eliezer. 28.3495 oz g 0.0353 À [email protected]. 28,349,523 oz μg 3.5274  10 8 À This is an open access article distributed under the 28,350 oz mg 3.5274  10 5 À CC BY-NC-ND license (https://creativecommons. 1 ppm μg·mL 1 1 org/licenses/by-nc-nd/4.0/). 0.9072 ton(s) Mg 1.1023 https://doi.org/10.21273/HORTTECH04679-20 ( F À 32) Ä 1.8 F C(C  1.8) 1 32 June 2021 31(3) 243 synonym later discarded in favor of attributed to the processing industry 1922–23 season. Most of the decrease “grapefruit” (Merrill and Lee, 1924; that commercialized canned juice, juice in U.S. grapefruit-bearing area oc- Zoller, 1918). The first commercial concentrate, marmalade, wine additives, curred in Florida; production in the shipments of grapefruit packed in bar- and candied peel. From 1932 to 1937, 1999–2000 season was 2,270,000 rels occurred from 1880 and 1885 grapefruit processing in Florida’s50can- tons, harvested from 114,100 acres from Florida to New York and Phila- neries increased from 80,000 to and declined to 180,400 tons from delphia. By 1889, grapefruit, though 420,000 tons of grapefruit annually. By 24,700 acres in the 2018–19 season. unfamiliar to most consumers, consti- 1936, Texas had 30 canneries (Heid, Acreage in Florida in 2020 reduced to tuted 6% to 7% of Florida’scitrusex- 1937) that processed 260,000 tons of 21,700 acres (USDA, 2020a). port (DePass, 1890). The great freeze grapefruit (about 157 million cans of HLB was first reported from Texas of 1895 drastically reduced all citrus juice) in the 1939–40 season, generating in 2012 (Kunta et al., 2012), but no sig- production in Florida (Humes, 1909), $7 million (Watson, 1940a, 1940b). By nificant reduction in fruit production has including grapefruit. By the 1909–10 1946, the U.S. production increased to been reported after 8 years of disease es- season, the United States produced 2,521,200 tons, of which Florida con- tablishment. In the1999–2000 season, 44,760 tons of grapefruit with 98% tributed 1,280,000 tons and Texas grapefruit production in Texas was contribution from Florida [U.S. De- 920,000 tons (TexSun News, 1948). 237,000 tons from 20,000 acres; in the partment of Agriculture (USDA), United States’ grapefruit acreage 2018–19 season, the yield was 244,000 1945]. increased from 28,800 acres in 1919 to tons from 16,000 acres. The reduction By 1915, Florida’sproduction 198,500 acres in 1947 as new produc- of acreage in Texas occurred because of area consisted of 16,000 acres of bear- tion areas were developed (Fig. 1). freezes,othercitrusdiseasescausedby ing and 45,000 acres of nonbearing, Freezes in 1951, 1962, 1985, and soil-borne pathogens such as Phytoph- 1- to 5-year-old grapefruit trees 1989 intermittently reduced both bear- thora nicotianae, and urbanization. (Vaile, 1915). During the same peri- ing area and production. A look at vari- In California, HLB was first re- od, the California industry had 600 ation in the planting area when freezes ported from a citrus plant in a residen- acres of bearing and 1100 acres of occurred shows that the reduction in tial area in 2012 (Civerolo, 2015); the nonbearing trees. The first commer- acreage was significant in Texas [data disease was restricted to backyard citrus cial grapefruit orchards were planted shown for 10-year blocks (Table 1)]. for 8 years. In 2020, a CLas-positive in Texas in 1915 and produced 120 The other states did not have such asian citrus psyllid was reported from a tons of fruit in the 1919–20 season drastic effects; in some regions, the commercial grove in southern Califor- (Vaile, 1915). planting areas increased after the nia (Citrus Industry News, 2020), in- Grapefruit production increased freeze. In Feb. 2021, grapefruit groves dicating disease spread. substantially from 1919 to 1944, in Texas were hit with a severe freeze, California’s total grapefruit pro- mainly in Florida and Texas. In Flori- with some groves showing a tempera- duction was 241,000 tons from da, in the 1919–20 season, the pro- ture of À7.2 C for several hours; dam- 16,600 acres in the 1999–2000 sea- duction was 236,000 tons; and by ages are still being evaluated (E.S. son and reduced to 128,000 tons 1943–44, it surged to 1,240,000 Louzada, unpublished data). During from 9000 acres in 2018–19 and to tons. In Texas, the production in- the years with most severe freezes, the 87,000 tons in the 2019–20 season.