Agriculture in Mesoamerica

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Domesticated plants and neglected crops in Mesoamerica
Beans (Phaseolus spp.)
Cucurbits (Cucurbita spp.)
Chayote (Sechium edule)
Custard apples (Annona spp.)
Grain amaranths (Amaranthus spp.)
Sapote (Pouteri a sapota)
Spanish plum, red mombin (Spondias purpurea)
Tomatillo, husk-tomato (Physalis philadelphica)

Domesticated plants and neglected crops in Mesoamerica

Physical geography and human occupation
Past cultures
Agricultural systems
Domesticated plants
Marginalization of crops in Mesoamerica

"In southern Mexico and Central America, the plant researcher finds himself, in the full sense of the term, in a veritable centre of creation."
(Vavilov, 1931)

Mesoamerica was defined by Paul Kirchoff in 1943 as the area of influence of Mexican cultures in the pre-Columbian era. Its boundaries are of course wide: the basins of the rivers Pánuco and Santiago mark its northern limit while its southern border runs from the Atlantic coast of Honduras along the Pacific slope of Nicaragua and the Nicoya peninsula of Costa Rica. In addition to being a cultural region, Mesoamerica is one of the areas of origin of agriculture, comparable with the Near East, China and the Andean region. Vavilov considered it to be the continent's most important "centre of origin" -nowadays referred to as centre of genetic diversity.

Physical geography and human occupation

Mesoamerica is a region of complex physical environments. Starting from the centre of Mexico, two mountain ranges stand out. They are the Sierras Madres, which run parallel to either coast and extend along other mountain axes, some of them with very active volcanoes, from the centre of Mexico to Panama. Between the ranges in Mexico, there are extensive, fairly flat and dry areas rising up to the central valley. Towards the southern end of the region, there are intermountain depressions and valleys which are intersected by rivers. The result is a very complex relief. Between the ranges and the coast, alluvial plains and the Yucatan peninsula spread out over limestone rock.

Mesoamerica's position. between the Tropic of Cancer and lat. 10°N places it in an area affected by great climatic forces originating in the surrounding oceans. The interaction of the climatic elements, latitude and relief creates a variety of environments, ranging from the coastal plains of the Atlantic, with a precipitation of 3 000 to 5 000 mm, to the semi-arid areas of Mexico. The region is principally divided into zones with continuous humidity on the Atlantic slope and zones with alternating seasons, including a dry period, on the Pacific slope. This period corresponds to the northern winter, which the Spanish called summer. The area with alternating seasons, which stretches from the Pacific coast to the mountain heights, was the first to be occupied by humans and is still the area with the greatest population density.

The plant cover is also very varied in Mesoamerica since the elements of northern origin -pines reach as far as Nicaragua, for instance merge with South American species, many of which have penetrated deep into the lowlands of both slopes in Mexico. Under these conditions, isolation and selection have naturally created a high level of biological diversity and consequent endemism. As in other tropical areas, the main landscapes are determined by the interaction of climate and relief, soil factors being of lesser importance.

The current landscape of Mesoamerica is defined by human occupation. In general, it gives the impression of a rather dry, highly eroded region, with original plant cover localized in small isolated spaces. Of the subdeciduous forest which covered the region from Sinaloa to Guanacaste, only small areas remain, some in Mexico and others in Costa Rica. In most of the countries, the agricultural boundary has broken down and the humid tropical forests are being reduced at such a rate that within ten to 20 years they will have disappeared.

Past cultures

The first inhabitants of Mesoamerica were immigrant groups from the north who advanced towards South America and formed small nomadic communities about 25 000 to 40 000 years ago. The first traces of utensils appear about 18 000 years ago and the first culture known was that of the Olmecs, a conglomeration of populations which extended from the coastal plains of the Gulf of Mexico to the highlands. A series of cultures, which occupied different areas and had separate periods of development, succeeded one another in Mesoamerica. There are remnants of their complexity and origins in the indigenous languages, which appear to be ancient and profound ramifications of a few basic stocks of North American origin. Some of the successive cultures became fully developed, progressing from settlements to empires. When the Spaniards arrived, Mesoamerica was not dominated, as were the Andes, by a hegemonic power. The Aztec empire coexisted alongside tiny independent tribes but the Aztecs were the chief power and their language, Nahuatl, virtually became a lingua franca throughout Mesoamerica. Plants, equipment for their cultivation and use and even soil types had Nahuatl names which were used from Sinaloa to Costa Rica, and some beyond the frontiers of Mesoamerica.

Agricultural systems

Agriculture was the basis of the Mesoamerican civilizations. It is estimated to have taken centuries to develop and its final stage - which became known to Europeans in 1500 - is thought to have been the result of an accumulation of practices and materials invented and perfected by the various cultures that had survived wars, famines and natural disasters. It cannot be assumed that this result was a linear process; it must have taken shape slowly in centres of economic and political power, expanding or contracting according to the fate of the human groups. Efforts to improve crops and invent production and utilization practices were undertaken more or less continuously and were perhaps safe from many hazards because activities were in the hands of farmers, who were the least affected by power changes.

From gathering plant products, people went on to protecting and cultivating certain plants. It is thought that fruit-trees, which supplied a good part of the produce gathered, were also the first species to be protected and cultivated. During the expedition to Honduras, the Spaniards of Cortés managed to survive thanks to the sapodillas which they found in the forest. One could imagine that the primitive seed plantings were similar to the ones that can still be seen in the plots of houses in some parts of Chiapas and Guatemala. These plots are a mixture of fruit-trees, edible and medicinal plants, cocoa and ornamental plants, sown and harvested without any order under native trees which serve no other purpose than to provide fuel and shade. There is nothing to indicate that selection was practiced under these conditions, nor that the types chosen were sown. In dry regions, primitive sowings could have been based on plants that produce seeds and require clean soil to grow. Eventually, the system of slash-and-burn clearing developed, and this is practiced in all regions. especially those with alternating seasons.

FIGURE 2 Mesoamerica

Another line of development was the control of soil humidity. Irrigation dates back to ancient times in Mesoamerica and, in the central valley of Mexico, it was practiced over very extensive areas using different systems. They did not reach the point of constructing engineering works as in Peru, but they did manage to cover sufficient areas to supply the big urban centres of Teotihuacán and Tenochtitlán. Major irrigation development began in the colonial period with the cocoa plantations, which extended this crop to new areas such as the Pacific lowlands as far as Sinaloa. In an opposite process. drainage systems for wet soil were invented, based on the construction of terraces. The most spectacular were the chinampas of the valley of Mexico. now reduced to a tourist attraction. They made a considerable contribution to Mexico City's food supplies before the conquest and during the colonial era. In the low-lying lands of Campeche and Veracruz, terraces were used from the time of the early cultures and were also developed on the lowlands occupied by the Mayas.

The development of agricultural systems depends to a great extent on labour implements and the availability of animal traction. Mesoamerica did not make a special contribution to either of these, however. Only the most primitive farming equipment was known: the coa a pointed stick for sowing seed, was in general use: in Mexico, coas and bronze spades were invented while, in other parts of the region, large shells were used for this purpose but no tillage implements were developed as they were in the Andes. The complete lack of draught animals was characteristic of the entire New World. Human resources provided the necessary energy while slavery, whether concealed or evident, enabled the dominant groups to acquire food, clothing and adornments through tributes. Regarding cultivation systems, methods and equipment, Mesoamerica did not contribute any new or special item that was not already known in other agricultural systems.

Among the Mesoamerican agricultural systems, that of the Mayas has received most attention. Much has been written in an attempt to understand how, in an extremely unfavourable environment with very poor soils and very abundant or scarce rainfall, a culture could develop whose advances in mathematics, astronomy and architecture were superior not only to those of other pre-Columbian cultures, but also contemporary European and Asian cultures. The construction of major urban centres must have required a great number of workers, and the subsistence of the latter and of the ruling classes cannot be explained satisfactorily by the region's current agricultural production system. Although partial theoretical explanations have been put forward. the question is still far from being resolved. It is known that the Mayas depended on three basic products - maize, beans and gourds as well as minor products, all of which were Mesoamerican. It has been argued, without any reliable evidence, that it was they who domesticated cocoa, although it has been proved that they prepared a kind of chocolate. Two other plants used and probably sown were Brosimum (breadnut or ramón) and Talisia spp., both fruit-trees. When the Europeans arrived, the Mayan culture had disappeared almost completely. Their descendants. particularly in Yucatan. practice a system of agriculture that does not seem to have changed much since the classic era.

Domesticated plants

It would be too academic an exercise to classify the plants of Mesoamerica according to their process of domestication into tolerated, cultivated and domesticated species as if these were distinct categories because plants occur in all the intermediate states as well. It has not been possible to identify the factors that allowed their domestication, but .some must be the same that favoured domestication in the Near East, Southeast Asia or China. On many occasions it has been stated that this process occurred at more or less the same time throughout the world but that it was slower in Mesoamerica.

The information available on domestication covers aspects such as botany (the existence of a great species diversity and of wild relatives), archaeology (plant remains, representations or impressions on utensils) and history and linguistics (documents, names in indigenous languages). Archaeological proof carries the greatest weight but is restricted to those species and regions whose conditions have favoured the preservation of organic remains and therefore allowed a correct identification and reliable dates to be given. Consequently, the information derived from archaeological evidence in Mesoamerica and in other regions of primitive agriculture must be gathered within these limits. Excluded are those species which do not preserve well and areas of high humidity which. according to Vavilov, might have been those with the oldest forms of agriculture.

Although Mesoamerica did not make any valuable contributions to cropping systems, in the domestication of plants its place is comparable to that of any other region, troth in the number and Importance of species domesticated. It is an absolute certainty that maize was domesticated in Mesoamerica and that, from the time when agriculture was first practiced (about 3 000 years ago), it already formed part of the earliest production systems along with a species of Cucurbita and Capsicum. With regard to maize, archaeological evidence discovered by MacNeish in Tehuacán, central Mexico, constitutes the most complete proof of the local evolution of a crop. In Mesoamerica, numerous variants or races were developed which adapted to almost all environmental conditions, from sites with high humidity and temperatures to areas at a height of 3 100 m with a cold dry climate.

Mesoamerica can be credited with having invented the greatest number of ways of eating and drinking maize products as well as the equipment and methods for preparing them. Lime was used to separate the husk from the grain, which increased its protein value and produced a top quality food. This was definitely a chance discovery which was not applied in other regions of the world. Among the uses of maize in Mexico, in 1520 Hernán Cortés cited the production of canes "which are as sweet and honeyed as sugar cane''.

At least three species of Cucurbita originated in Mesoamerica: Cucurbita argyrosperma, perhaps the first to be cultivated, which is suited to altitudes between 0 and 1500 m: C. moschata , the most common and useful, which is found between 300 and 1 500 m, and C. pepo, which is less important in Mesoamerica than in Europe and the United States and which grows up to an altitude of 2 000 m. A fourth species, C. ficifolia is eaten in a different way from the others and may also originate in Mesoamerica.

Among the cucurbits, two species of Sechium are also grown: Sechium edule (chayote), whose fruit, roots and tender stems are eaten and whose distribution is very wide in the American tropics (its centre of origin is Mexico and Guatemala); and S. tacaco although this is restricted to its original area, the highlands of Costa Rica.

The tomato (Lycopersicon esculentum) was first known in Mexico, where it was described in detail by Francisco Hernandez around the period 1571 to 1577. It was not of great importance as a vegetable, as it was an extra plant in the maize fields although its fruit was the size of modern varieties.

A vegetable with a similar use is Physalis philadelphica, commonly called tomato or husktomato in Mexico; it is also grown in Guatemala and a few varieties of it are preserved.

The Mesoamerican species of chili, Capsicum annuum, from which peppers are derived, has wild populations and a very broad varietal diversity in this region.

The common bean, Phaseolus vulgaris, appeared about 5 500 to 7 000 years ago in central Mexico where wild populations of it abound, but intensive cultivation of it began between the first and seventh centuries. P. coccineus, a perennial species of high ground, was already to be found in Mexico about 2 200 years ago; another very similar species, P. polyanthus, is grown together with P. coccineus; and P. acutifolius, which was grown about 5 000 years ago in Tehuacan, extends from the United States to Costa Rica.

One of the main crops of pre-Columbian Mexico was Amaranthus hypochondriac us. whose seeds were eaten in the same way as cereals. Another species cultivated, especially in Guatemala, is A. cruentus.

Native roots and tubers have not been important in Mesoamerican agriculture. The yam bean (Pachyrhizus erosus) is an ancient crop which is nowadays very widespread. The potatoes of Mexico's highlands, of great value as an energy food, produce small edible tubers but are not cultivated.

Cacao (Theobroma cacao), which is found growing wild in southern Mexico, was possibly domesticated in this region where there are aberrant varieties, and its pre-Hispanic cultivation did not go beyond the present frontier between Costa Rica and Panama.

Upland or hairy cotton (Gossypium hirsutum) is the most extensively grown fibre plant; one of its centres of domestication seems to have been the Gulf of Mexico and archaeological remains in that country indicate that it was known about 5 500 years ago. Other fibre plants, today replaced to a great extent by synthetic fibres, are henequen (Agave fourcroydes), sisal (A. sisalana), A. angustifolia var. letonae of El Salvador and several species of Furcraea.

Of the leaf vegetables, mention should be made of Crotalaria longirostrata, Solanum americanum , S. wendlandi Cnidoscolus chayamansa. Chenopodium berlandieri spp. nuttalliae and Opuntia leucantha, which are eaten fresh or cooked, as well as the tender stems of Cucurbita and Sechium species. The inflorescence of Chamaedorea tepejilote (pacaya) is a widely consumed item in Mexico and Guatemala, but its cultivation is still limited to kitchen gardens. The chayote (Sechium edule) is used for its fruit, roots and tender stems.

Probably the majority of domestications has occurred with fruit-trees. Archaeological remains of some of them exist, although it is not known with any certainty whether they were gathered or cultivated. Annona diversifolia, A. reticulata and A. scleroderma are natives of Mesoamerica and wild populations of some of them are known; Casimiroa edulis is cultivated from sea level up to 2 500 m; archaeological remains dating back 5 000 years have been found. This is a complex species because of its different local populations. Couepia polyandra and Diospyros digyna, exhibiting numerous varieties, grow wild from Mexico to Costa Rica and also date back about 5 000 years. Inga jinicuil and I. paterno originate from Mexico and El Salvador, respectively. Licania platypus is found from Mexico to Panama; Manilkara zapota, with numerous varieties, is now grown in all tropical areas. Persea americana, the avocado pear, is one of the fruits which, in Mesoamerica, are grown at any altitude between 0 and 2 500 m; wild populations of this plant still exist. The following also grow: Parmentiera edulis, Persea schiedeana. Pouteria campechiana, P. sapota, the sapote and a related population, P. viridis: Pouteria hypoglauca, Prunus capuli, Psidium friedrichsthalianum, and Spondias purpurea. with many varieties and uses. In Mexico, there are numerous wild cactus species whose fruits are gathered and there is an incipient cultivation of a few species.

Spices and condiments include Capsicum annum and C. frutescens : Pimenta dioica, which grows wild from Mexico to Costa Rica and whose cultivation dates back to ancient times; Vanilla planifolia produced more outside the region: and Fernaldia pandurata Some spices are obtained from semi-wild plants, such as penduliflorum chufle (Calathea sp.) and Quararibea funebris.

Fermented drinks (pulque) or fresh drinks (maguey juice) were known in the pre-Columbian period and are obtained mainly from two species of Agave, A salmiana and A. mapisiga. The origin of the preparation of distilled drinks (mescal. tequila) obtained from A. tequiliana and other species also dates back to that period.

There are a great number of medicinal plants, most of which are in the early stages of cultivation. Mesoamerica's most recent contribution has been the Dioscorea species which is used for the production of diosgenin-cortisone and is grown for this purpose in Mexico.

No less important are ornamental plants. The Spanish found gardens in Mexico similar to those of Europe and. in the centuries following the conquest, numerous species of orchids and bromeliads from Mesoamerica have been grown in Europe and the United States. A group of Compositae, Ageratum Cosmos Dahlia. Tagetes and Zinnia which were cultivated in the region from the pre-Hispanic period, have been intensively selected in Europe and the United States. Wild populations are to be found of all of these genera as well as of Tigridia, Zephyranthes, Euphorbia and other ornamentals.

Marginalization of crops in Mesoamerica

Of the causes which contributed to the neglect of certain crops. the replacement of a natural product by a synthetic one has perhaps been the most drastic. The indigo (Indigofera spp.) agroindustry, which still has a great commercial importance. has now almost been entirely displaced by the production of chemical dyes, while Agave and Furcraea have been replaced by synthetic fibres. The rubber plant (Castilla elastica), whose use was already known in pre-Hispanic times, was a budding crop at the turn of the century but it was then replaced by a more efficient plant Hevea brasiliensis, which was in turn replaced by synthetic rubber.

In food plants, marginalization has been a longer and less straight forward process. Culinary preparation and eating habits instilled from childhood have result' d in the permanence of these species. However, violent social changes such as the conquest brought about profound alterations. Indigenous products were replaced by introduced products which competed with the former and were :favoured by the prestige attached to them by the dominant social group. Indigenous crops were abandoned first of all by the upper social strata and then by the lower strata. Only the very poor communities and indigenous populations maintain the traditional crops as well as the methods for handling and using them.

The change, based or social prestige, occurred without taking into account the intrinsic value of the crops, for instance their nutritional properties or production costs. In El Salvador, a comparative study between native vegetables, such as chipilin or tachipilin (Crotalaria spp.) and hierba more or nightshade (Solanum americanum) and European vegetables (lettuce, cabbage), showed the superiority of the former as sources of vitamins and amino acids, not to mention that their production requires less care and costs for fertilizers and insecticides.

The non-acceptance of a crop because of its lack of social prestige is reflected in many aspects. Growers in Guatemala can obtain credit on their citrus fruit but not on such a prized local fruit as the papausa (Annona diversifolia in spite of the fact that the latter has a good market. Moreover, there are no extension services for native crops, perhaps because a knowledge of them is part of the heritage of the indigenous people.

Many foreign technical experts concentrate on exotic crops and not on native ones, as their experience, information and extension equipment relate only to the former. On the other hand, it is frequently foreign anthropologists who draw attention to native crops and, in particular, to the processes known to the indigenous communities regarding their use.

There is one interesting case of marginalization, that of huautli or prince's feather (Amaranthus hypochondriacus). which is dealt with in a later chapter.

Numerous Mesoamerican crops have not expanded beyond limited areas. The chaya or spurge (Cnidoscolus chayamansa is cultivated in Yucatan and Peten; the ixtlán (Solanum in southeastern Guatemala; the loroco (Fernaldia pandurata) in El Salvador; the (Chenopodium berlandieri) in central Mexico. There are local studies on agronomic handling of most of these plants and it is possible that some might expand to new areas.

The future of neglected crops in Mesoamerica depends on the combined action of several factors. One is research on production and handing , aimed at obtaining superior varieties and improved agronomic practices, especially in protection against pests and diseases.. Another is establishing reliable and permanent sources of seeds and other propagating material and making them available to growers. Fundamental to this process are agricultural extension campaigns that show the advantages of the neglected crops over exotic ones as regards their nutritional value and ease of production.

These aspects require intensive study and an evaluation of? varieties, traditional production systems and ways for indigenous groups or rural workers to utilize the products in order to adapt them to modern methods. Furthermore, a study must be made of market conditions and the possibilities of widening the market to other regions, while research should be done on the way the product is presented as well as on the standards which guarantee the consumer a stable quality and promote a wider acceptance. The diversification of uses in agro-industries will create new market possibilities and provide a guarantee for the producer.

Bibliography

Bukasov, S.M. 1931. The cultivated plants of Mexico, Guatemala and Colombia. Bull. Appl. Bot. Genet. Plant Breed. 47: 1-553. Turrialba, Costa Rica, CATIE-GTZ.

Dressler, R.L. 1953. The pre-Columbian cultivated plants of Mexico. Bot. Mus. Leafl. Harv. Univ 16: 1 15-172.

Flannery, K.V., ed. 1987. Maya subsistence. New York. Academic.

Harrison, P.D. & Turner, B.L., eds. 1 978. Pre-Hispanic Maya agriculture e. Albuquerque, USA. University of New Mexico Press.

Martinez, M. 1959. Las plantas útiles de México. Mexico City, Botas.

Palerm, A. & Wolf, E. 1961. La agriculture y el desarrollo de la civilización en Mesoamérica. Rev. Interam. Cienc., Soc., 1: 1-345.

Rojas Rabiela, T. 1988. Las siembras de ayer. La agricultura indigena del siglo XVI. Mexico City, SEP-CIESAS.

Rojas Rabiela, T. & Sanders, W.T., eds. 1985. Historia de la agricultura Epoca prehispanica siglo XVI, (2 vole). Mexico, INAH.

Vavilov, N.I. 1931. Mexico and Central America as the principal centre of origin of cultivated plants in the New World. Bull. Appl. Bot. Genet. Plant Breed., 26: 135-199.

Beans (Phaseolus spp.)

Phaseolus coccineus
Phaseolus acutifolius
Phaseolus lunatus
Phaseolus polyanthus

Of the genus Phaseolus sensu stricto which includes 55 species, five have been domesticated. The pre-Columbian peoples grew them for thousands of years as a main source of protein, since animals did not have an important role as a source of food or draught power, particularly in Mesoamerica.

As early as the pre-Columbian period, the kidney bean (P. vulgaris L.) had gained wider acceptance and was selected more intensively. The early chroniclers inform us that, in the Aztec and Incan empires, great importance was given to this species and it was used to pay tributes. It gained even more popularity after the conquest and, from 1880, with the exception of isolated studies the work on genetic improvement was mainly concentrated on this bean. This preferential treatment was detrimental to the other species which are of greater or comparable interest in modern agriculture, at least in areas that do not offer optimum ecological conditions for their development.

The ancestral form of P. vulgaris is grows within the boundary between two climatic zones subtropical dry and tropical temperate - where pre-Columbian societies established many settlements, a fact which may explain the acceptance of the species. To cover the greater part of the area occupied (except for certain Andean regions), the Pre-Columbians domesticated four other species.

The five ancestral forms were lianas which grew in different ecological niches. Biochemical studies have shown how P. lunatus was domesticated in several points of Mesoamerica and P. vulgaris in the Andes. Except in the latter region, uniformity in selection pressure led to a considerable similarity in evolutionary stock. With the exception of the tepary bean, the association with maize -although it was late in the Andes - also contributed to this standardization. The levels of evolution of the five species have been varied and there is a great potential for exploitation; for example, as regards the growth habit in P. polyanthus and the size and colour of the P. acutifolius seed. The ecological potential of these species would enable some of them to be developed even more profoundly than P. vulgaris is.

At a time when the model of an agriculture which is both sustainable and productive has been accepted, beans deserve to be given renewed attention.

Phaseolus coccineus

Botanical name: Phaseolus coccineus L.
Family: Fabaceas
Common names. English: scarlet runner bean; Spanish: ayocote (name of Nahuatl origin, central Mexico), patol (Mexico [Zacatecas]), botil (Mexico [Chiapas]), chomborote, piloy (high plateau of Guatemala), cubá (Costa Rica)

This species has been cultivated in the high parts of Mesoamerica for many centuries. In pre-Columbian Mexico. the people of the Anahuac cultivated it extensively and ensured its distribution. Its introduction into southern Colombia (Antioquia and Nariño) and Europe (where it is known as scarlet runner bean and haricot d'Espagne) could have occurred in the seventeenth century before reaching other parts of the world, such as the Ethiopian highlands. It has been found in archaeological remains only in Mexico in Durango and Puebla, and wild only in Tamaulipas. Although archaeological information is very scarce, it could be assumed that its Mexican domestication took place in humid high zones.

Changes in maize varieties (earlier-maturing and with softer stems) and the use of fertilizers (for example, urea) and herbicides in maize fields led to the gradual abandonment of this crop in eastern Guatemala and in Costa Rica. It is reasonable to suppose that the same is happening in other areas of its cultivation. Because of its ecological niche, P. coccineus has suffered heavy competition from exotic crops with a higher consumption and better market, for instance vetch, broad bean, cabbage, garlic and onion.

P. coccineus has been used in its nuclear area, particularly for its dry or green seeds. The consumption of young seeds enables the crop to be expanded to higher altitudes. since the fleshy root produces a second growth after light frosts (for example in Huehuetenango, Guatemala). The root of this legume has medicinal uses in Mexico and the flowers are also eaten. Its gaudy influorescences may be the reason for its recent expansion as an ornamental plant in Europe and the United States. The green pod is used as a vegetable in western Europe and the dry seeds (white seeds) are eaten in some traditional dishes.

Botanical description

A pluriannual species of great vegetative vigour, with stems of several metres (only in a few modern cultivars are there shrubby forms) which emerge from a fleshy root, P. coccineus is easily distinguished by: its large seeds (the weight of 100 seeds is 80 to 170 g and 6 to 12 g for the wild from)) and small, narrow. elliptical hilum; and its large influorescences (20 cm and in excess of 20 fruit-bearing stems) with scarlet, white or, more rarely, two-colour flowers. It carries out hypogeal germination, has a fleshy root which is divided and generally fusiform and which allows cotyledonary young shoots to resprout over several consecutive years. It flowers 50 days after sowing, with early varieties, or at the start of the rains, and continues to produce flowers over a long period, except in the shrubby varieties. In the majority of cases P. coccineus at undergoes cross-pollination, assisted by its extrorse stigma and nectaries and through the action of bees and humming birds. Thus far, it is considered self-compatible.

The seed of wild varieties is dispersed through explosive dehiscence of the pods during the dry period. In some wild populations there is a short latency; the seed's viability in natural conditions does not exceed three years.

Ecology and phytogeography

Like P. polyanthus, P. coccineus tolerates higher precipitations than other species of Phaseolus(Table -3), provided that the soil has good drainage; that is with derivatives of volcanic ash, fine particles, etc. It grows at cooler temperatures than other cultivated species and is generally heliophytic, although it tolerates mists.

FIGURE 3 Beans: A) Phaseolus coccineus; A1) legume; A2) seeds; B) P. acutifolius; B1) legume; B2) seeds

Its nuclear area extends from Durango to Veracruz and Puebla. In Guatemala. it is traditionally sown on the slopes of the Cuchumatanes range, on the high plateau of Huehuetenango up to Alta Verapaz and Sacatepequez, and in the highest parts of the rest of Central America. The wild form of P. coccineus (although unable to be confirmed as ancestral throughout its distribution) extends from Chihuahua in Mexico to Panama, generally between 1 400 and 2 800 m in the humid high forest.

Genetic diversity

In its wild lone, this species displays a great phenotypical variation in its current state of evolution, in contrast with the other wild species of the genus (there is some similarity with P. of South America). Wild P. coccineus may be considered to be a complex of several forms, now in active speciation, throughout its distribution range. Some very differentiated forms, such as P. glabellus may have become separated. constituting an early from of a group of which it is now difficult to distinguish all the variants Allogamy is frequent in these plants, and the crossing of wild and cultivated forms, which have been displaced by humans, has changed the speciation patterns. Because of its active process of evolution, this species complex is not an easy task for the taxonomist but, by the same token, it offers great potential for the plant improver.

In addition to a group of four wild forms with scarlet flowers, mention should be made of another four forms with purple flowers. P. polyanthus is a related species at the boundary of the primary genetic stock of the scarlet runner bean, since in some cases it can be crossed with the latter, as in Putumayo, Ecuador or in Imbabura, Colombia. Likewise, P. vulgaris may be considered to be at the boundary of the primary genetic stock of the scarlet runner bean.

There are only a few definite cultivars, particularly among the climbers; among the indeterminate shrubby cultivars, "Patol Blanco" may be mentioned and, among the determinate shrub cultivars, "Hammond's Dwarf.

There are risks of genetic erosion in areas where the traditional maize field has been changed, as some parts of Mexico (Chiapas, Oaxaca, Puebla and Veracrul), Guatemala and Costa Rica. Along with maize, the three species of bean (P. coccineus, P. polyanthus and P. vulgaris) and gourds were frequently sown in these areas. In the high plateau of Mexico (Durango. Zacatecas), the recent spread of the kidney bean may displace the "patoles" for reasons of cost.

P. coccineus material exists in collections of germplasm, mainly in Chapingo in Mexico (INIFAP), Pullman in the United States (USDA) and Palmira in Colombia (CIAT). The cultivated material has already been collected to a great extent. except in some areas of Guatemala (for example, Quiche), Honduras and Costa Rica, where it may be already too late to make such a collection.

For the wild material, it is necessary to collect around the great cities of Mesoamerica, particularly in the valley of Mexico, since these areas were a centre of diversity of the P. coccineus complex which is very rich in forms. Many areas still remain to be explored, in view of material collected compared with the abundant herbarium material available. The complications involved in handling these forms ex situ mean that they need to be conserved in situ.

Cultivation practices

In most of its nuclear area, P. coccineus is sown with maize and other varieties or species (P. vulgaris is, P. polyanthus) following documented practices, since precipitations allow their association. In Durango and Zacatecas (Mexico), under heavy rain conditions it is sown alone. either in widely spaced rows or broadcast. depending on the type of ploughing. Manual harvesting is still common: the pods are gathered and left to dry in the sun before being beaten and the seeds are stored in sacks.

TABLE 3 Selected cultivated species of Phaseolus: altitude, daytime temperature, mean annual precipitation, duration of growth cycle from start to end of harvest, yield potential in tropical areas

Species Altitude

(m)

Temperature

(c)

Precipitation

mm/year

Growth cycle

(days)

Yield

(kg/ha)

Phaseolus coccineus 1 400 - 2 800 12 -22 400 -2 600 90 -365 400 -4000
Phaseolus acutifolius 50 - 1 900 20 - 32 200 400 60 -110 400 - 2000
Phaseolus lunatus 50 - 2 800 16 26 0 -2 800 90 -365 400 -5000
Phaseolus polyanthus 800 - 2 600 14 - 24 1 000 - 2 600 110 - 365 300 - 3500
Phaseolus vulgaris 50 -3 000 14 -26 400 -1 600 70 - 330 400 - 5000

Estimation of the yield in cultivated fields is difficult, since farmers intercrop P. coccineus with other beans or harvest it periodically. It produces 400 to 1088 kg per hectare in the scrub by forms while, for climbing varieties, the yield can be much higher (Table 3). In the United Kingdom, for crops with young pods, more than 23 tonnes per hectare have been recorded.

Prospects for improvement

The scarlet runner bean has been used on many occasions for Improving the common bean but only in very few cases has its own Improvement been addressed, although specialists agree on the hardiness of the species against several fungi, bacteria and viruses.

The delayed production of climbing forms may he considered a limitation. The number of shrub by forms is not sufficiently high (especially of those with white seeds) and several of them have a low yield. Not all colours and seed stocks exist in these varieties. and this is particularly the case with shrubby forms. Floral abscission can at times be considerable - perhaps because of the lack of pollinators - and causes yield losses.

Many cultivars root easily and can be maintained over several years thanks to their fleshy root. Their large attractive flowers make insect pollination easy (this crop may be assumed to have a positive effect on local entomofauna). A hybrid scarlet runner bean could be developed; however, unlike the kidney bean or the tepary bean, it is not known whether there would be a strong heterosis effect.

The use of the scarlet runner bean to complement maize in silage deserves investigation since, as well as its fodder value, the plant can limit soil erosion. It may also be useful interspersed in young forest or fruit plantations (to give soil protection, fertilizing value or additional income).

Because of its type of germination, P. coccineus species for fighting the bean fly (Ophiomya phaseoli) in the highlands of East Africa.


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