Unraveling the origin of CoVea arabica 'Bourbon pointu' from La ...

Euphytica DOI 10.1007/s10681-009-9886-7

RE V IEW

Unraveling the origin of CoVea arabica ‘Bourbon pointu’ from La Réunion: a historical and scientiWc perspective Aurélie Lécolier · Pascale Besse · André Charrier · Thierry-Nicolas TchakaloV · Michel Noirot

Received: 27 August 2008 / Accepted: 14 January 2009 © Springer Science+Business Media B.V. 2009

Abstract CoVee is one of the main products on the international markets, in association with oil, corn, sugar, and paper pulp. The history of coVee-tree cultivation is incompletely documented, both regarding its domestication in Africa, and its assisted dispersal throughout the world. This review focuses on the coVee mutant, CoVea arabica ‘Laurina’ (Chevalier A in Encyclopedie Biologique. Vol 28, 1947), also named ‘Bourbon pointu’. This plant is generally acknowledged to have been selected in the island of ‘Bourbon’ (La Réunion) from a Weld at the beginning of the 19th century. Compared with the common ‘Bourbon’ variety, ‘Bourbon pointu’ trees are dwarf,

A. Lécolier · P. Besse University of the Réunion, UMR PVBMT, Pôle de Protection des Plantes, 97410 Saint Pierre, La Réunion, France

with a characteristic Christmas-tree shape and the beans have an excellent cup quality. Although cited many times in literature, the origin of this variety is ambiguous and is largely discussed even today with increasing confusion, particularly in books and local newsletters. This article provides a thorough historical and bibliographical review of coVee cultivation in La Réunion, which leads to an understanding of the bottleneck responsible for the low genetic diversity of the ‘Bourbon’-type modern varieties. Complemented by a review of the scientiWc studies conducted on this subject, conWrmation of the veracity of the various historical accounts becomes possible, and appropriate conclusions on the origin of the ‘Bourbon pointu’ are derived. Although historical texts provide important information and represent priceless resources that give direction to scientiWc research, it is clear that this same research makes it possible, in turn, to clarify and to interpret historical texts.

A. Charrier Montpellier-SupAgro, 2 place Viala, 34 000 Montpellier, France

Keywords CoVea arabica · Geographical origin · Natural mutation · Molecular markers · La Réunion

T.-N. TchakaloV Conseil Régional de la Réunion, Musée des Arts Décoratifs de l’Océan Indien, 166 route de Cilaos, At. 1, 97421 La Rivière Saint-Louis, La Réunion, France M. Noirot (&) IRD, UMR PVBMT, Pôle de Protection des Plantes, 97410 Saint Pierre, La Réunion, France e-mail: [email protected]

Introduction CoVee is the most important agricultural commodity after palm oil (Vega et al. 2003). Among the 103 species identiWed (Davis et al. 2006), only two species, with distinct organoleptic qualities, produce 99% of coVee:

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(1) CoVea arabica L. (ARA) preferentially cultivated in the highlands and preferred by the consumers due to its low bitterness, its aromatic characteristics and its low caVeine content. Its production represented 65% of global coVee production for the year 2005–2006 (www.ico.org/documents/icc967f.pdf); (2) C. canephora Pierre ex Froehn (CAN), more suitable for intertropical lowlands, is characterized by a stronger bitterness and higher caVeine content. These two coVee species are commonly referred to Arabica and Robusta, respectively. ARA is the only natural polyploid species (2n = 44) of the genus, the other species showing 2n = 22 chromosomes (Krug 1934; Leroy and Plu 1966; Louarn 1972). Its meiotic behaviour is diploid-like (Medina 1950; Mendes 1950; Mendes et al. 1954; Grassias and Kammacher 1975). Presence of two genomes in ARA has been suggested from the meiotic behaviour of haploids (Berthaud 1976; Carvalho 1952; Vishveshwara 1960) and F1 hybrids (at triploid, tetraploid and hexaploid levels) between this species and other CoVea species (Berthaud 1978; Chinnappa 1968; Kammacher and Capot 1972; Louarn 1976; Medina 1963; Monaco and Medina 1965). The presence of a C. eugenioideslike genome as female parent of ARA has been emphasized from chloroplast DNA sequence comparisons (Berthou et al. 1980; Cros et al. 1998). On the other hand, sequences of the internal transcribed spacer region (ITS2) of the nuclear ribosomal DNA shows high similarity with corresponding sequences in canephoroid species (CAN, C. congensis, and C. brevipes) (Lashermes et al. 1996). Finally the possible presence of the C. eugenioides-like genome and the CAN-like genome within the ARA genome has been conWrmed using genomic in situ hybridization (GISH) (Lashermes et al. 1999; Raina et al. 1998). ARA is self-compatible with a residual allopollination rate of 7–13% (Carvalho and Krug 1949; Charrier et al. 1978). In contrast, diploid species are selfincompatible (Charrier and Berthaud 1985), with the exception of three species—C. heterocalyx (Coulibaly et al. 2002; StoVelen et al. 1996), C. charrierii (StoVelen et al. 2008), and C. anthonyi (StoVelen et al. 2009, in press). On a genetic point of view, selfpollination leads to the emergence of homozygous lines and allows Wxing recessive alleles and selecting

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mutants. This has been clearly underlined in Brazil with the discovery of numerous mutations, such as angustifolia, crespa, erecta, semperXorens (Carvalho 1946; Krug 1949). ARA is mainly native from Ethiopia (Gole et al. 2001; Guillaumet and Hallé 1967, 1978; Meyer 1965; Sylvain 1955; Tadesse and Nigatu 1994; Tewolde and Egziabher 1990; Vayssière 1961) with additional populations in South-Sudan (Boma plateau) (Thomas 1942) and North-Kenya (Mount Marsabit) (Anthony et al. 1987; Githae et al. 2007). The diversity of the species in wild forests is large (Vayssière 1961) and this has been recently conWrmed using molecular data (Aga et al. 2003; Anthony et al. 2002; Tesfaye et al. 2007). This contrasts with the low diversity among ARA cultivated varieties. Two distinct groups of cultivated varieties are distinguished by genetic analysis using random ampliWed polymorphic DNA (RAPD), ampliWed fragment length polymorphism (AFLP), and simple sequence repeat (SSR) markers (Anthony et al. 2001, 2002; Lashermes et al. 1996; OrozcoCastillo et al. 1994). These two groups are represented by ‘Bourbon’- and ‘Typica’-derived accessions, respectively. Tesfaye et al. (2006) conWrm the common origin of the ‘Typica’ and ‘Bourbon’ genetic bases: they are derived from the same pool of Ethiopian coVee introduced to Yemen. In fact, the low diversity observed in cultivated varieties results from severe genetic bottlenecks of historical origin (Anthony et al. 2002; Tesfaye et al. 2007). The history of coVee cultivation is incompletely documented with regards to the domestication of coVee plants in Africa and their dispersal throughout the world by man (Berthaud and Charrier 1988; Charrier and Berthaud 1985). CoVee exploitation may have begun at the end of the 5th century in southwestern Ethiopia (Lejeune 1958). ARA coVee plants could have then been introduced to Yemen as early as 575 AD (Wellman 1961). At the end of the 17th century, the Dutch East Indian Company started to establish the coVee planting industry in Indonesia. In 1710, a single plant was introduced to the Amsterdam botanical gardens from Java (Cramer 1913). Some of the young seedlings obtained from this tree were taken to Surinam in 1718 (Cramer 1913). From there, an ARA coVee tree was introduced in the West Indies (Martinique) in 1720 or 1723 (Candolle (de) 1883). It became the parent of numerous selfed-progenies further disseminated around the world (Jamaica, Puerto

Euphytica Fig. 1 Morphological characteristics of CoVea arabica ‘Bourbon’ (on the left side of each picture) and of CoVea arabica ‘Bourbon pointu’ (on the right side of each picture). a General tree shape—tree of ‘Bourbon’ had a size of 2m20, the one of ‘Bourbon pointu’ 1m75, b leaves—picture height: 10.2 cm, c seeds—picture height: 3.3 cm

Rico, Haiti, Cuba, the Central America, the Guianas, Brazil, etc.). All these introductions constitute one of the two genetic bases at the origin of most of the commercial Arabica cultivars grown worldwide, and described as C. arabica ‘Typica’ Cramer. The second genetic basis, described as C. arabica ‘Bourbon’ (B. Rodr.) Choussy, has been developed from coVee trees introduced to the island of Bourbon (presently La Réunion) from Mocha. It will be thoroughly described throughout this paper. In La Réunion, a novel variety, called ‘Bourbon pointu’ (BP) with a Christmas-tree shape, smaller internodes, and smaller leaves (Fig. 1) than ‘Bourbon’, has been selected for its drought resistance from ‘Bourbon’ Welds at the beginning of the 19th century (Chevalier 1947; Raoul 1897; Villèle (de) 1920). The name of the BP is derived both from its origin (island of Bourbon: La Réunion) and the sharp extremities of its seed (Fig. 1c). BP is also known under other informal names, such as ‘Leroy’, after the name of the coVee grower who selected the Wrst BP trees, or ‘Laurina’, due to its resemblance to a laurel (Chevalier

1947). It was disseminated worldwide by man from La Réunion under these names during the 19th century. BP is appreciated for its very low caVeine content of 0.5–0.7% dry matter basis (dmb) (Baumann et al. 1998; Chaves et al. 2004; Mazzafera and Magalhaes 1991; Mazzafera et al. 1992; Tango and Carvalho 1963), compared to 1.1% dmb for ARA and 2.2% dmb for CAN (Ky et al. 2001). It is especially acknowledged for its organoleptic quality. Sir Winston Churchill and Honoré de Balzac were among its most famous drink-addicts. This coVee of high organoleptic quality is today compared with the wellknown ‘Blue Mountain’. The coVee expert PierreHenri Massia, coauthor of the “Passion du Café”, describes it as the “best coVee in the world” (Massia et al. 1995). The objective of the present article is to provide a thorough historical and bibliographical review of coVee cultivation in La Réunion and to clarify the possible origins of BP. It clearly appears that the records and the bibliography revolve around four main hypotheses regarding this origin:

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(1) a natural mutation of the ‘Bourbon’ genetic base appeared in La Réunion; (2) a second introduction from eastern Africa; (3) a hybrid between the ‘Bourbon’ genetic base and the endemic C. mauritiana Lam. of La Réunion; and (4) an endemic species from La Réunion. This historical review is complemented by new scientiWc results on this subject. It then becomes possible to draw conclusions on the origin of the BP variety and to conWrm or not the veracity of the various historical accounts.

History of coVee cultivation in La Réunion The history of coVee cultivation in La Réunion in the 18th century is similar to that of all tropical plants with value-added products. Because coVee consumption increased very much in Europe as early as the end of the 17th century, the French commercial company, created by Colbert in 1664 (La compagnie des Indes), considered coVee-tree cultivation as an appropriate opportunity to develop the island of Bourbon (Maurin and Lentge 1979). In 1714, Pontchartrain, Minister to the King, sent letters to several vessels departing to the island of Bourbon, specifying them to collect coVee trees from Mocha (Yemen). According to Hardancourt (the old director of the Compagnie des Indes), there was a French agent by the name of Imbert leaving in Mocha at that time, who had succeeded in getting 60 coVee trees (Hardancourt (d’) 1664–1719). The king of Yemen had given them to him because he was then in good terms with the French people, who had cured him of an ear abscess in 1712 (Pontchartrain 1713). Just before the introduction of coVee trees from Mocha to La Réunion, a local wild coVee tree, hurriedly named café marron,1 was discovered by d’ Hardancourt (1664–1719) during an excursion in the mountains of La Réunion. He took some of the plants back to mainland France to test their quality. “This coVee is bigger than the Mocha one and sharp-pointed at the extremities” (Hardancourt (d’) 1664–1719). 1 Marron = maroon coVee. In French, the term ‘marron’ was used for slaves who escaped into the wild from their place of slavery. Subsequently, it was also used for some plant species growing in the wild in La Réunion.

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Antoine de Jussieu, a botanist of that time, described it as “diVering from the Bourbon coVee because it is longer, Wner, greener” (Jussieu 1716). This coVee, distinct from all the other species and endemic to La Réunion and Mauritius (Chevalier 1940; Cordemoy (de) 1972; Dulloo et al. 1998), was botanically described under the name of C. mauritiana Lam. (Lamarck 1783). It grows in a conical shape to a size of 2–5 m. Its solitary Xowers also distinguish it from the grouped Xowering pattern of ARA. Among the 60 plants of ARA received from Mocha, 20 were delivered to La Réunion on the 25th September 1715, the others having perished during the navigation. The precious plantlets were entrusted to the care of two inhabitants of Saint Denis, the Martin brothers, who were instructed to maintain them and take special steps to multiply them (Archives 1717; TchakaloV et al. 2007). According to Haarer (1956), only two plants survived out of the 20 in their care. This information attests the diYculties the early farmers had to face during the Wrst introductions and cultivation of a new plant species. The discovery of an endemic coVee tree and the successful introduction of these two ‘Bourbon’ trees from Mocha created enthusiasm and launched coVee cultivation on the island, in spite of certain diYculties in obtaining seedlings. By the middle of year 1718, the hopes of the island relied on (i) the sole survivor of the two remaining plants of ‘Bourbon’ (ii) the 117 young seedling progenies obtained from this survivor, and (iii) the indigenous C. mauritiana. Nevertheless, little by little, the inhabitants gave up C. mauritiana and switched over to the sole cultivation of the ‘Bourbon’ coVee, native to Mocha. At the end of 1719, 779 novel trees were obtained by seed multiplication from the sole survivor, reaching a total of about 7,000 trees 1 year later (Guet 1888). In 1727, 250,000 pounds of coVee beans were yielded, and this production was increased ten-fold in 1744 (Maurin and Lentge 1979). This period of prosperity lasted until the 1800s, when a conjunction of various factors brought about the decline of the coVee culture (cyclones of 1806 and 1807, coVee-rust epidemic in 1810, and competition with coVee from Martinique on the French market). It was progressively replaced by sugar cane (Archives 1854–1857; Billiard 1822; Lougnon 1958). To summarize, coVee trees were introduced into La Réunion from Yemen. The plantation and Welds mainly progressed from one tree, which was largely

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multiplied during the 17th century. This period of seed propagation considerably favoured the Wxation of various alleles leading to the ‘Bourbon’ variety. Simultaneously, C. mauritiana, an endemic coVee tree from La Réunion and Mauritius, was discovered, but its cultivation was quickly abandoned due to its poor organoleptic quality (stronger bitterness) compared with that of ARA.

The diVerent historical hypotheses for the origin of the ‘Bourbon pointu’ According to Raoul (1897), the BP appeared in La Réunion: “[It] comes from a tree selected at the beginning of the century in a place called Ravineaux-chèvres, which was part of Mr. Auguste Pajot’s lands. The latter gave it the name of his agent, a former sailor named Roy or Le Roy, who had discovered it”. “Formerly, the bean coming from Leroy coVee tree was very long; through cultivation, it lost its typical form, but it nevertheless remained rather acute at one of its ends to justify the name of ‘Bourbon pointu’. It was adopted by the growers around 1810, because of its dryness resistance, at a time when the Moka2 coVee started to grow less than in the Wrst times of its culture in the Weld”. Nevertheless, for some authors, the BP coVee has an African origin. The writings of these authors are often travel accounts, stories, or collections on the history of the island of Bourbon. Auguste Billiard (1822) wrote: “A new variety of coVee tree, known in the colony under the name of coVee Le Roy, it is (I believe) the same one as the one known in the West Indies under the name of “coVee of Ethiopia”; they both originate from the Eastern coast of Africa; approximately twenty-four years ago, seeds … were introduced by a captain who sowed them and distributed the young seedlings to some farmers of the windward part [of the Island]. Mr Le Roy, having bought a property in the district of Sainte Marie, where some coVee-trees had been destroyed, recognized that a patch of a characteristic species had been saved, which was nothing else than the coVee tree of Africa”. Antoine Roussin, at the time of his 2 The cited Moka here is not C. arabica var. moka (Hort. Ex Heynth) Cramer, but the ‘Bourbon’ introduced from Mocha in the 18th century, which used to be cultivated in La Réunion.

trip to La Réunion around 1880, agreed with this hypothetical introduction of the BP (Re-edited in 2004). Emile Trouette (1898) proposed in his booklet the possibility that this coVee had been “introduced from the African coast in 1771 by Wolf, a German traveller [who gave seeds to Mr Bourdier, engineer in Bourbon]”. Nevertheless, for Villèle (de) (1920), the German navigator Wolf could have brought to the island of Bourbon some seeds of a new coVee tree discovered by himself in Africa in 1770, but nothing in the reports indicated that it was the BP. The interspeciWc hybridization origin constitutes the following hypothesis. Villèle (de) (1920) considered, as Raoul (1897), that BP appeared spontaneously in La Réunion, and consequently, he looked for possible explanations for this emergence. For him, BP could have resulted from a cross between the wild coVee tree C. mauritiana and ARA. His opinion was based on two observations: (i) seeds are shapepointed in both C. mauritiana and BP; and (ii) caVeine content of BP seeds was halfway (0.440) between the wild coVee C. mauritiana (0.00) and ARA (0.820) (Bénard 1918). A fourth hypothesis was emitted to explain the spontaneous emergence of BP when the notion of mutation spread over world. This hypothesis was strengthened by the emergence of other mutations in Brazil such as angustifolia, crespa, erecta, semperXorens (Carvalho 1946; Krug 1949) and the observation of reversions to the type ‘Bourbon’ (Chevalier 1947). Lastly, the BP was recently considered as an endemic coVee tree of La Réunion: “When man settled in La Réunion, there were on the island two wild coVees: the “café marron” and the “café pointu” (Rivière 2006). This hypothesis is based on the known existence of the endemic coVee tree C. mauritiana in that region (as one species was present, why not two?) and the high biodiversity existing in La Réunion [it belongs to one of the hotspots of world biodiversity (Myers et al. 2000)].

The very low genetic distance between ‘Bourbon’ and ‘Bourbon pointu’ AFLP analyses (Vos et al. 1995) were carried out to estimate the genetic distance between BP and ‘Bourbon’.

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Euphytica Table 1 Number of bands observed per AFLP primer combinations

E.AAG/M.CAT

53

E.ACT/M.CAG

65

E.AAG/M.CAA

24

E.AAG/M.CTT

37

E.ACA/M.CAG

76

E.ACA/M.CTC

41

E.ACT/M.CTC

42

E.ACT/M.CAT

41

E.AAG/M.CTA

37

E.AAG/M.CTG

60

E.AGG/M.CAA

55

E.AGG/M.CTC

43

E.ACT/M.CTG

64

E.ACT/M.CAC

48

E.AGG/M.CAG

78

E.AGG/M.CAG

70

E.ACG/M.CTT

40

E.ACG/M.CTG

45

Analyses were applied on ten progenies obtained through self-pollination of one tree per variety. The experiment was carried out twice and only repeatable markers were taken in account. A total of 919 markers were recorded from 18 primer combinations (Table 1), only one band diVerentiated the BP samples from the ‘Bourbon’ ones, all the other markers (918) were always present in all progenies. This genetic similarity was also conWrmed on a sample of six ‘Bourbon’ accessions and six BP accessions from La Réunion. This allows calculating a Nei genetic distance (Nei 1972) between the two progenies of 0.0005. This result can be compared with AFLP results obtained by Anthony et al. (2002) using 11 subspontaneous accessions from Ethiopia, three ‘Typica’-derived accessions from Brazil, Jamaica and Mexico, and four ‘Bourbon’-derived accessions from Brazil and La Réunion. Whereas 94 AFLP markers among the 107 analyzed ones are polymorphic within subspontaneous accessions, only seven and 14 were polymorphic within the ‘Typica’derived and ‘Bourbon”-derived accessions, respectively (Anthony et al. 2002). Similarly, the genetic distance between the ‘Bourbon’ and BP progenies of 0.0005 can be compared with the distance of 0.187 between ‘Typica’ and ‘Bourbon’ (Anthony et al. 2001). This emphasizes the very low genetic distance between ‘Bourbon’ and BP.

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Comparison between the four historical hypotheses using the recent scientiWc accounts All the diVerent historical hypotheses emitted can be examined systematically, thanks to scientiWc analyses. These include recent data on interspeciWc hybridizations, cytogenetic studies on the CoVea species complex, and phylogenetic and genetic diversity analyses obtained using molecular markers. The interspeciWc-origin hypothesis The interspeciWc-origin hypothesis is the easiest to reject. When crossing a diploid CoVea species with a tetraploid one, several results are expected: (i) most hybrids are triploids (Berthaud 1978; Carvalho and Monaco 1968; Krug 1934) with some very rare exceptions at tetraploid, pentaploid, and hexaploid levels when unreduced gametes are implied; (ii) triploid hybrids are strongly sterile (1–2% of fertility) mainly due to the chromosomal unpairing during meiosis (Charrier 1976); (iii) a large genetic distance is expected between the interspeciWc hybrid, and ARA. Indeed, C. mauritiana and ARA, the two supposed parental species of this interspeciWc hybridization, are among the most distantly related species within the genus (Maurin et al. 2007); and (iv) subsequently, an interspeciWc hybrid should lead to highly variable progenies. Moreover, such a strongly sterile hybrid would be counter-selected by coVee growers and could only have emerged in the wild forests. In particular, the restoration of the full fertility requires several generations, which, in the wild forests, would consist in backcrosses with C. mauritiana or selffertilizations. In all cases, the number and the diversity of hybrids should increase. It is surprising in this condition that such diversity was not noticed during the second part of the 18th century. In contrast, BP is tetraploid (Krug 1934), fully fertile, genetically very close to other ARA varieties, especially from ‘Bourbon’, and gives very homogeneous progenies. In conclusion, the hypothesis suggesting an interspeciWc origin of the variety BP has to be rejected. The African-introduction origin and the endemic-origin hypothesis The genetic distance between two independent samples depends on the ARA diversity. For example,

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when taking in account ‘Bourbon’ and ‘Typica’, the Nei’s genetic distance is 0.187 (Anthony et al. 2001). This is 374-fold the genetic distance between ‘Bourbon’ and BP. Moreover, both ‘Bourbon’ and ‘Typica’ came from the Arabia peninsula, for which the diversity results from a Wrst bootleneck process: the introduction from Ethiopia (Anthony et al. 2002; Tesfaye et al. 2007). Indeed, the Nei’s genetic distance between ‘Bourbon’ and the subspontaneous Ethiopian ARA varied from 0.164 to 0.373 (Anthony et al. 2001). Consequently, it is rather implausible to obtain such a low distance by random sampling of two independent introductions, one from the Arabian peninsula, the other from Ethiopia. It is like to randomly sample two twin brothers. The same argumentation as for African-introduction hypothesis can be applied to the endemic-origin hypothesis. Indeed, before or after the 17th century, introduced naturally or by man, the problem is similar: two independent introductions should lead to a larger genetic distance than observed. In addition, BP should be as frequent as C. mauritiana in the native forests of the island, and this is not the case. The mutation-origin hypothesis Krug et al. (1954) point out that the F1 hybrids between ‘Bourbon’ and BP are of the Lrlr type and present a ‘Bourbon’ phenotype; thus, the alleles Lr and lr are dominant and recessive, respectively. In the F2 generation, the segregation is 3:1 (2,066 ‘Bourbon’ and 663 BP plants obtained in the progenies). This genetic Mendelian inheritance was conWrmed by back-crossing the F1 with ‘Bourbon’ (100% of ‘Bourbon’ phenotypes in the progeny) or with BP (50% ‘Bourbon’ and 50% BP in the progeny). These results are typical of a Mendelian inheritance of a single gene without segregation distortion, where Lr and lr are dominant and recessive alleles, respectively (Krug et al. 1954). As the phenotype BP diVers from the phenotype ‘Bourbon’ by several traits (Christmas shape, dwarf internodes, lower caVeine content, etc.), this gene has pleiotropic eVects. The allele lr can be considered as resulting from a mutation of the allele Lr in a plant showing the genotype LrLr. In addition, the reversions of the mutation are known (Chevalier 1947) and are currently observable in Nouvelle Calédonie with the presence of ‘Bourbon’ branches on BP trees (Le Pierrès, personal

communication). Reversion phenomena also have been observed for numerous other species (examples: Linaria vulgaris—Cubas et al. 1999; Arabidopsis thaliana—Stokes et al. 2002; Antirrhinum majus L—Bollmann et al. 1991; and Solanum esculentum L—Manning et al. 2006). These reversions suggest an epigenetic origin, due to for example methylation or transposons (Martienssen 1996). If the hypothesis of a mutation is no longer any doubt, the mutant allele could have occurred either in La Réunion or in Mocha (Yemen) and subsequently emerged as homozygote genotype lrlr in La Réunion. Nevertheless, this last hypothesis is unlikely for two reasons: (i) there is no record of coVee tree showing a Christmas-tree shape, dwarWsm and long and sharppointed seeds which would have been observed in any of the east African countries between the 17th and the 20th centuries; (ii) if the sole survivor from Mocha present in La Réunion in 1717 was heterozygote Lrlr, 25% of homozygous lrlr genotypes are expected within the Wrst progenies (896 trees) obtaining by selWng between 1717 and 1719. Consequently, the most likely hypothesis is the emergence of the mutation of a ‘Bourbon’ tree in La Réunion, its Wxation as homozygous genotype lrlr by selWng, followed by its selection and its multiplication by seeds as pure line.

Conclusions This review emphasizes the importance of linking historical information and scientiWc analyses. It reinforces the hypothesis suggesting that the BP resulted from a mutation, called laurina, which might have taken place in La Réunion two centuries ago from the ‘Bourbon’ genetic base introduced from Mocha. Because of its mode of reproduction (about 93% selWng) and the sowing of seeds obtained at harvest time, the recessive mutation can be Wxed very quickly in a homozygous genotype. It might have been detected in this state and then propagated because of its resistance to drought and its desirable organoleptic qualities. When taking in account the epigenetic mutation hypothesis, its pleiotropic eVect is still to analyse. In particular, how to explain the observed results about its caVeine content at the origin of the Villèle’s (de) hypothesis? Indeed, caVeine content is often recorded as additive in intra- and inter-speciWc hybrids involving

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coVee species with caVeine, whatever the ploidy level (Barre et al. 1998; Berthaud 1977; Capot 1972; Charrier and Berthaud 1975; Le Pierres 1987; Louarn 1976). Moreover, it has been conWrmed that the caVeine content in BP seeds [0.5–0.7% dmb (Baumann et al. 1998; Chaves et al. 2004; Mazzafera and Magalhaes 1991; Mazzafera et al. 1992; Tango and Carvalho 1963)] is halfway between C. mauritiana [0% dmb (Bertrand 1902)]—and ARA [1.2% dmb of caVeine content in average in wild accessions (Ky et al. 2001)]. Nevertheless, caVeine content in BP seeds does not diVer from that in C. eugenioides [0.51% (Campa et al. 2005)], one of the putative parental species of ARA. The mutation laurina could suppress the genetic eVects of the C. canephora-like genome present in the ARA on the caVeine content, resulting in a C. eugenioides-like phenotype for this trait. Finally, the high likehood of the mutation hypothesis allows comparison between BP and ‘Bourbon’ to analyse and identify the genomic origin of the mutation. This was the prerequisite condition for further investigations using these two varieties. Acknowledgments This study was Wnancially supported by the European Union, the Conseil Régional of La Réunion and the Institut pour la Recherche et le Développement (IRD). Lécolier Aurélie had an Allocation Régionale de Formation Doctorale (Conseil Régional of La Réunion and European Social Fund).

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