The northern perimeter of the Amazon Basin – Upper Orinoco and Guianas
PART 2: THE CIRCUM-CARIBBEAN REGION
In accordance with the discussion of the subject in previous chapters the spontaneous origin of the populations in the Region, as defined in Chapter 1, is debatable. However, even though the diversity that existed in pre-Columbian times did not emerge from spontaneous origins in the region, it is appropriate to consider it separately from the Amazonian Region on account of the special characteristics of the varieties that it comprises. The fact that cacao was
cultivated, or occurred in other forms, in the Region prior to the arrival of the Europeans in the New World is undisputed. It is also necessary to take into account the importance of the Region as a producer of cacao. In the first instance this involved, primarily, consumption by the original inhabitants and later as an important, and sometimes the only, supplier of cocoa when the product became an object of consumption outside the Region.
The basic distribution area of cacao in the Circum-Caribbean Region as we can conceive as existing in the pre-colonization period could be divided into three geographical zones. One of these comprises the area in the north of the South American mainland, which appears to have been located to the west and southwest of the Lake of Maracaibo in what originally came under the government of Nueva Granada. It is essential to understand that prior to the independence of the countries in northwestern South America and the formation of the present day states the entire region was under a single government. Therefore, the pre-Columbian distribution of cacao and the development of cultivation before independence apply to the whole of the Reino de Nueva Granada and this fact needs to be appreciated in order to dispel any misconceptions regarding the role of the individual countries.
The other distribution areas that are components of the Region are those that occur in Mesoamerica (Mexico and Central America), for which we should consider a possible southern limit of the pre-Columbian distribution as the southern shores of Lake Nicaragua and the rivers that empty into it. These distribution areas are divided by the central cordilleras into a Pacific coastal zone and an eastern or Caribbean seaboard zone. It is intended to give a separate description of the situation in each zone on the assumption that their formation may have involved genetic elements from different sources or different evolutionary paths.
In view of the fact that virtually no reliable descriptions exist regarding the characteristics of the cacao varieties that existed in these zones at the time of the arrival of the Europeans, any attempt to describe the nature of the populations that inhabited each area would be speculative. It would be possible to arrive at a general picture of the situation as it may have existed by means of the genetic analysis of the present-day varieties that are presumed to be descendants of the pre-Columbian populations.
The difficulties that are presented in the determination of the nature of the parental varieties are based on two situations. One is that, through the expansion of the areas of cultivation in order to meet the increasing demand for cocoa, the definition of the primary distribution areas has become blurred.
Although the varieties established in the areas into which cultivation expanded would be descendants of the primary diversity they need not necessarily reflect the variability that existed in the parental populations. It would be expected that, on the one hand, variability may have been increased through mutation and recombination and, on the other hand, alterations in the genetic base would have resulted from natural and directed selection in the long period during which the expansion took place.
The other aspect that affects the diversity existing in the present day populations in the Region is related to the importation of other varieties,
particularly those associated with the Amazonian Region, either in their original form or as the products of hybridization. It will be demonstrated in subsequent discussions of the composition of the present day cultivated populations and inheritance that it is sometimes impossible to distinguish, on the basis of phenotypic characteristics, between the prototype varieties and descendants of their hybrids that possess similar features.
While the areas in which the prototype Criollopopulations are distributed have undergone substantial changes in their structure, principally on account of the superior qualities of imported germplasm, it is important to consider the fact that some of the basic diversity has been conserved in other countries. This conservation has come about owing to the importation of varieties from the Criollopopulations, primarily to satisfy interests relating to product quality. The scant attention paid to the descendants of these introductions by the persons involved in research on the Criollodiversity is regrettable.
The basic situation regarding the genetic diversity of cacao in the three distribution zones is that the archetypal varieties possess several common features. It is because of this situation that it is appropriate to consider the populations of the Circum-Caribbean Region as a genetic entity. In accordance with the definition given in Chapter 2 the title of Criollo will be used throughout the book to identify the populations and individual genotypes that may be assumed to belong to this variety concept.
In common with most of the concepts concerning cacao diversity, that of Criollois subject to different interpretations based on the information available to, or on the whims of, the persons who propose to identify the components of this section of the species’ diversity. The subject of an acceptable definition of a
‘variety’ within the concept of Criollo has preoccupied many persons since studies of cacao varieties began in the second half of the 19th century. J.H.
Hart set out to define the concept in an article discussing the characteristics of Criollo (Hart, 1908). Perhaps this article and similar publications defining the common varieties that existed in Trinidad during that period, as will be described in the discussion of the evolution of the cacao populations of that island, form the basis of the concept that has been used since then. Various other authors, such as Cheesman (1944), have dealt with the subject and evolved additional interpretations from their own experience or other sources of information.
With regard to the characteristics that are applied to define the varieties that belong to the Criollo group, it is commonly assumed its members have elongate fruits with long acute or attenuate apices. Other characteristics included in the definition are the rough and ridged surface, a thin or soft husk and large seeds with white cotyledons (Bailey, 1947).
The principal characteristic of the varieties that may be attributed to the concept of Criollo, which is common to all distribution zones and which distinguishes them from the previously held notion of an Amazonian variety, is the presence of anthocyanin pigment in the fruits. The factors that produce this character have pleiotropic effects on the pigmentation of other organs of the plants. The main effect associated with red fruits is the presence of pigment in the leaf axils and pulvini, which is normally expressed in the leaves of
developing flushes. It is to be expected that these factors also produce the development of anthocyanin pigment in the flush leaves, but the expression of flush leaf pigment is not exclusive to genotypes with red fruits. Some variations in pigment of flower parts are associated with the presence of the fruit pigment factors. However, the penetrance of the pigment factors may depend on other genes carried by particular genotypes that result in variations in the intensity of pigment and the homozygosity status of the loci concerned. Other factors include the reaction of the genotypes to environmental conditions, such as the intensity of light. The presence of the fruit pigment factor also has an influence on the level of pigment in the cotyledons (an expression that is not usually appreciated). This relationship will be explained in the section of Chapter 7 that deals with the inheritance of these expressions. Additionally, the presence of the allele responsible for the pigmentation in the fruits is exhibited as pigmentation in the hypocotyls of the germinating seeds.
However, it is necessary to emphasize that, as demonstrated in the discussion of the Amazonian Region populations, fruit pigmentation also occurs in those populations, sometimes to a significant degree. Accordingly, the red fruit phenotype is not exclusive to the Criollopopulations but in the absence of studies of the inheritance of the Amazonian phenotypes it would be premature to suggest any relationship between the phenotypic appearances of the varieties from the two Regions.
An understanding of the nature of the pigment expressions in the Circum- Caribbean aboriginal varieties is important in recognizing their contribution to the ancestry of many hybrid genotypes. On this basis it can be concluded that, apart from other evidence, the ancestor of any genotype possessing red fruits would be a red-fruited Criollo genotype even though it exhibits other traits that may be completely different from any of the Criollotraits (for an example, see Fig. 36).
Research on the system of reproductive compatibility that operates in cacao conducted during the second half of the 20th century revealed that the Criollo genotypes used in breeding programmes possibly possessed a genetic mechanism that differed from the Amazonian Region genotypes with which they had been combined in hybridization. The research on this subject has lacked the continuity of effort required in order to elucidate the genetic differences between the two groups of diversity involved. Further details on the subject will be provided in the discussion of the inheritance of the compatibility systems.
The other trait that appears to occur exclusively in varieties belonging to the Criollopopulations is that in which the plants do not form the normal whorl of five plagiotropic branches (jorquette) from the terminal buds of the orthotropic stems but, instead, a single plagiotropic branch. So far, this trait has not been recorded in the Amazonian populations.
Flowers of many Criollogenotypes are often of large size. In these flowers the appearance is that of laxity with the presence of long straps connecting the petal hoods to the ligules. However, such characters are not universally expressed and it is possible to encounter genotypes that undoubtedly correspond to the Criollogroup but that produce very small flowers.
One feature that previously was considered to be unique to some of the Criollopopulations is the formation of fruits with the arrangement of the ridges
in the fruit form known as ‘Pentagona’. However, as has been demonstrated, this character also occurs in the Amazonian populations and can no longer be considered a unique characteristic of the Criollo group. In fact, the character does not occur uniformly in all of the Criollopopulations, in which case it is not specific to the group.
Other features that have in the past been considered as specific to the Criollo populations include the soft husk of the fruits, large seed size and unpigmented cotyledons. The large seed size is not universally encountered. It is usually associated with genotypes having large fruits and low ovule or seed numbers. In these cases the negative correlation between seed numbers and seed weights applies. The high seed weights are not transmitted to the hybrid progenies of such genotypes in the same way that the factors carried by Amazonian varieties with seed weights of similar magnitude are transmitted to their progenies. It has been shown in the discussion of the Amazonian Region diversity that in certain populations genotypes can be encountered whose phenotypes express all of these traits, either singly or in combination.
The subject of seed weights and seed numbers in the populations belonging to the Criollo group involves the general occurrence of low ovule numbers. These probably never exceed 50 and it seems likely, although no reliable data have been obtained that will show the range of ovule numbers, that some varieties have numbers inferior to 40. Low ovule numbers would set serious limitations on the reproductive capacity of the genotypes concerned, decreasing their aptitude for use for commercial purposes.
It is evident that a considerable degree of genetic variability occurs in the archetypal varieties of the Circum-Caribbean Region when taken as a whole.
The variability expressed by genotypes that could be ascribed to these varieties, or to their relatives with similar phenotypes, renders it inappropriate to consider all of these varieties as being strictly related. Cheesman (1944) suggested that it would be inappropriate to apply the term ‘variety’ to these populations and suggested that the term ‘Criollogroup’ would serve the purpose. He proceeded to describe the characteristics of the types of the regional populations known to him and made it abundantly clear that the diversity was so marked that no definition of the group name would be satisfactory.
However, in spite of this evidence, Cuatrecasas (1964), in his monograph of the genus Theobroma, presented a definition of the cacao types attributable to the concept of Criollo. This definition, which has no botanical basis, is unfortunate in the sense that some persons assume that only genotypes that exhibit the traits so defined belong to the group. Unfortunately, as a result of the unnecessary adherence to the narrow definition, given by Cuatrecasas, which is based on fruit characters only, a tendency exists to disregard other genotypes that are also members of the Criollogroup but which do not exhibit the characters covered by his definition.
In the following sections an attempt will be made to describe the history and variety situation in each of the distribution zones. It is necessary to take into consideration the paucity of reliable details concerning the prototype genetic materials that formerly constituted the cultivated and sub-spontaneous populations of the Region. This situation prevents the development of a comprehensive and
accurate description of the situation in each zone. In addition, it should be appreciated that much of the available information is derived from sources that involve personal interpretations based on observations made in a limited range of the populations belonging to a given distribution zone.
Further, much of the personal knowledge about the diversity of the Region is based on material introduced into other countries where the genotypes have been subjected to investigation of one kind or another. It can never be assumed that these genotypes represent the true range of the diversity concerned. From the author’s point of view the personal knowledge of the populations in their native habitats is fragmentary or lacking, as is the case of the Mesoamerican populations. Consequently, it not claimed that the following account is correct or complete. It is intended to provide the best interpretation of the information available, including the author’s own experience.