Identification of Prosopis juliflora and Prosopis - Universidad Pública ...

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12DiscussionThe value of molecular markers in clarifying the taxonomy of the genusProsopis has been demonstrated in this study and in an earlier work byRamı´rez et al. (1999). Results from RAPDs analysis mostly confirm thoseobtained from flavonoid studies (Solbrig et al. 1977) and electrophoresis ofseed proteins (Burghardt and Palacios 1997), which divide Prosopis intoidentifiable sections and species. Morphological analysis has also generally, butnot always, agreed with these findings (Pasiecznik et al. 2001; Harris et al.2003) and most recently, ploidy determination has helped to distinguishP. juliflora from other Prosopis species. However, the results obtained fromRAPDs analysis need to be treated with caution. The presence of a speciesspecificmarker in this study distinguishes the species only from others testedand does not guarantee that a similar band may not occur in other, as yetuntested, species. The use of bulked DNA from 10 seedlings, in some casesfrom more than one mother tree, allows the possibility that some individualgenotypes of a species might lack the specific marker. For example, the speciesspecificmarker for P. pallida in this study occurred in all, and only in, samplesthat were also identified as P. pallida on the basis of leaf morphology andploidy. This suggests that the molecular marker was effective in identifyingP. pallida among the samples in this study even if there is some risk in applyingthe technique to identify a single P. pallida individual in future.Ramı´rez et al. (1999) analysed Prosopis species from Asia, Africa and SouthAmerica. The present study aimed to analyse species from North and CentralAmerica that were not included in the earlier work, thereby extending thecoverage of the native range of the genus. Two of the species studied,P. chilensis and P. cineraria were common to both studies. In the present study,molecular markers were also applied to resolve the long-standing taxonomicconfusion regarding the identity of P. juliflora and P. pallida, especially whereintroduced. Although molecular studies have been applied to resolve taxonomicissues in the Argentinean centre, there has, until now, been no molecularstudy in the region from Mexico to Peru, where P. juliflora and P. pallida arefound and which is the origin of most of the material now widespreadthroughout the semi-arid tropics.Ramı´rez et al. (1999) found a molecular marker (S11 (730) ) which could beused to identify New World Prosopis species. In addition, markers were foundthat were specific to each of the New World sections Monilicarpa, Strombocarpaand Algarobia (Ramírez et al. 1999). In the present study, six markerswere found in all species from section Algarobia, which were absent inP. cineraria (section Prosopis) and it could be suggested that these were specificto section Algarobia. One of these (S07 (1160) ) was also found by Ramı´rez et al.(1999). This strongly suggests this marker as genuinely specific to sectionAlgarobia, now observed in 12 species of the section (series Ruscifoliae, Pallidaeand Chilenses), but was absent in P. kuntzei Harms (series Sericanthae)(Ramı´rez et al. 1999).
Pasiecznik et al. (2001) noted similarities between P. juliflora and P. pallidasufficient to lead them to treat the two species together as the P. juliflora–pallida complex, based on their overlapping geographic range, being the onlytruly tropical American Prosopis species, and having similar morphology andresource characters. The marker L01 (520) was found in both P. juliflora andP. pallida but not in the other species tested, and along with the high similarityindex (0.73), this supports the hypothesis of Pasiecznik et al. (2001). However,recent work has suggested a clear division of these species using ploidy (Harriset al. 2003), although further detailed studies are still required in areas of thenative range where both species have been identified in sympatry to fullyconfirm this.Although this paper did not aim to look for molecular markers specific toNorth American species, the data obtained could differentiate them but alsoclearly show a equivalently high similarity value at 0.70 among P. glandulosa,P. laevigata and P. velutina. Jua´rez-Mun˜ oz et al. (2002) used RAPDs to studythe inter- and intra-genetic variation between four wild Mexican populations ofP. glandulosa, P. laevigata and P. juliflora and found a genetic variation of72.48% between them and 27.52% within them, and postulated that P. julifloragave rise to the other two species. It may be postulated that these NorthAmerican species could be grouped together into a species complex as has beensuggested by Pasiecznik et al. (2001), and South American species of sectionAlgarobia also show patterns of clustering (Ramírez et al. 1999).Several authors have observed that sympatric Prosopis species, where noreproductive isolation exists, are able to form stable fertile hybrids (Hunzikeret al. 1975; Simpson 1977a). Hybrids have been identified in North AmericaJohnston 1962; Solbrig et al. 1977) and South America (Hunziker et al. 1975,1986; Burkart 1976; Saidman 1985, 1990). Tentative evidence for a P. pallida· P. chilensis hybrid was provided by this study. Burkart (1976) described aputative hybrid between P. juliflora and P. pallida in northern Ecuador butnoted that it could be a form of P. juliflora var. horrida (Kunth) Burkart.Johnston (1962) noted that P. inermis H.B.K. (syn. P. juliflora var. inermis(H.B.K.) Burkart) may be a synonym of P. pallida. Harris et al. (2003) haveidentified a putative hybrid of P. juliflora and P. pallida in Cape Verde based onploidy, but suggest that while hybrids may form they could be sterile.Pasiecznik et al. (2001) also divided the P. juliflora–pallida complex intothree geographically distinct groups; (1) Peru and Ecuador, (2) Colombia,Venezuela and the Caribbean islands, and (3) Pacific coastal Central American.Accessions from groups 1 and 3 were analysed in this study and found to begenetically distinct. Range-wide analysis is, however, required in order tofurther elucidate the genetic relationships within the P. juliflora–pallida complex.Burkart (1976) divided section Algarobia into six series. According toBurkart (1976), P. chilensis, P. juliflora, P. glandulosa, P. laevigata andP. velutina are all of series Chilenses, while P. pallida is in series Pallidae. Thisstudy clearly differentiated P. pallida and P. juliflora from each other and from13
Page 2: 2species are sympatric in each cent
Page 7 and 8: 7presence or absence of each marker
Page 9 and 10: 9Figure 3. Amplification of the mar
Page 11: 11Table 3.Matrix of similarity amon
Page 15 and 16: of pod coloration. Burkart (1976) n

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