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Beans

(Phaseolus spp.)


The author of this chapter is D.G. Debouck (International Board for Plant Genetic Resources [IBPGR], Rome).

The author wishes to express his thanks to G.F. Freytag (USDA), J. León (University of Costa Rica), G. Ballesteros (University of Córdoba, Columbia), O. Toro (CIAT) and O. Youdivich. He also thanks the following institutions: IBPGR (Rome), CIAT (Colombia), IUCN (Switzerland), INIFAP (Mexico), ICTA (Guatemala), ICA (Colombia), INIAP (Ecuador), INIAA (Peru), CIF (Bolivia), INTA (Argentina) and the University of Costa Rica


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 grows within the boundary between two climatic zones subtropical dry and tropical temperate where pre-Columbian societies established many settlements, a tact 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.

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: Fabaceae

Common names: English: scarlet runner beans: Spanish: ayocote (name of Nahuatl origin, central Mexico), patol (Mexico [Zacatecas]), botil (Mexico [Chipas]), chomborote, piloy (high platear 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 yields 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 form) 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 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 seeds viability in natural conditions does not exceed three years.


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

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.

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 1400–2800 12–22 400–2600 90–365 400–4000
Phaseolus acutifolius 50–1900 20–32 200–400 60–110 400–2000
Phaseolus lunatus 50–2800 16–26 0–2800 90–365 400–5000
Phaseolus polyanthus 800–2600 14–24 1000–2600 110–365 300–3500
Phaseolus vulgaris 50–3000 14–26 400–1600 70–330 400–5000
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 Sacatepéquez. 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 1400 and 2800 m in the humid high forest.

Genetic diversity

In its wild form, 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. augusti 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 form 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 he 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 later, as in Putumayo, Ecuador or in Imbabura, Colombia. Likewise, P. vulgaris may he 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 Veracruz), 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 he conserved in situ.

Cultivation practices

In most of its area P. coccineus is sown with maize and other varieties or species (P. vulgaris, 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.

Estimation of the yield in cultivated herds is difficult, since farmers intercrop P. coccineus with other beans or harvest it periodically. It produces 400 to 1000 kg per hectare in the shrubby 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 be considered a limitation. The number of shrubby 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 is a useful species for fighting the bean fly (Ophiomyia phaseoli) in the highlands of East Africa.

Phaseolus acutifolius

Botanical name: Phaseolus acutifolius

Family: Fabaceae

Common names. English: tepary bean: Mayan: xmayum (Mexico [Campeche]): Spanish tépari, (name of Opatan origin) (Mexico [Sonora]). escomite or escumite (Mexico [Chiapas]), frijol piñuelero (name of hybrid origin) (Costa Rica)

This species has been grown for a long time in Mesoamerica, mainly as a vegetable in desert zones or areas with a long dry period. Unlike the case of other cultivated species of the genus, P. acutifolius was first described in its wild form while the relationship with the cultivated form was recognized later Archaeological findings have shown that this species was grown in ancient times in the southeastern United States, where it apparently penetrated from Mexico 1200 years ago) and Puebla (where it existed 5000 years ago). Geographical distribution of the cultivated form extends from Arizona and New Mexico to Guanacaste, Costa Rica, on the dry subtropical slope of the Pacific. The distribution of P. acutifolius is sporadic, which is reflected in its market. The main product is a dry seed which is eaten because of its rich protein ( 17 to 27 percent) and carbohydrate content It is also used as a young tender string bean and as fodder after harvesting.

It is still not known precisely where the species was domesticated It should be noted that electrophoretic analyses of the phaseolin and isoenzymes indicate that the domesticated populations were few. Either because of its historic extinction, because the initial genetic base was already reduced at the time of its domestication or because of the autogamy of the species, the cultivated genetic potential does not seem to have been very extensive, to judge from its sub sequent development. Following are some of the causes that several authors have reported as having led to neglect of the tepary bean:

Its cultivation potential in desert areas is extensive and is still to be explored

Botanical description

P. acutifolius is a desert therophyte and is easily distinguished from other species of beans by its epigeal germination, sessile primary leaves, acute rhomboid folioles, pseudoracemes—with two to four fruit-bearing stems—small pink flowers (white in some cultivars) with very small triangular bracteoles and pods that have sutures marked with five to ten ovules Autogamy appears to be dominant Two wild forms are recognized: var. acutifolius with rhomboid folioles and var. tenuifolius with linear, sometimes sagittate, folioles. A third wild form appears sporadically with narrowly falcate folioles which. because they have different blastogenic characteristics from the var. tenuifolius and possess a certain incompatibility for crossing. could be considered a separate species (P. parvifolius).

Thc cultivated form, like the wild forms, has a short cycle, flowering 27 to 40 days after germination and ripening at 60 to 80 days. The plants wither completely (except P. parvifolius). In the wild forms, seeds are dispersed within a radius of 3 m by explosive dehiscence of the pods In some cultivars there is a brief postharvest latency of one month. The seeds of the wild plants germinate through the imbibition caused by the heavy desert rainfalls of the following year. However, only in some is germination staggered over three years.

Ecology and phytogeography

The cultivated form is found from 50 m to 1920 m above sea level. It requires an annual precipitation of 250 to 300 mm, although it is grown in Mexico in regions with a precipitation of 150 mm (Sonora) to 750 mm (Campeche). During the vegetative period, the daytime temperature can reach 20 to 32°C. It grows on well drained. sandy, muddy, sometimes organic soils with pH 6.7 to 7.1.

There is an ecological specialization in the wild forms of the tepary bean: var. acutifolius of Arizona, New Mexico, Lower California, Sonora, Chihuahua, Durango, Sinaloa and Jalisco occupies semi-sunny habitats with the mesquite on the banks of streams. while var. tenuifolius colonizes the sunny slopes with cacti and thorny shrubs in Arizona, New Mexico, Lower California. Sonora, Chihuahua, Durango, Sinaloa, Nayarit, Jalisco, Querétaro, Michoacán, Guerrero, Oaxaca and Jalapa. The cultivated form is a heliophyte and has characteristics that allow it to tolerate excessive sun.

Genetic diversity

Compared with the kidney bean, there is less seed variability. Basically two forms occur: one with a fairly small, rounded, white or black seed; and another with a larger-sized angular, rhombohedric seed that may be white, greenish white, grey, bay, dark yellow, mahogany, black or purple-mottled or coffee in colour. The average weight of 100 cultivated tepary bean seeds is between 10 and 20 g and, for the wild form, between 2 and 5 g. Two cultivars have been cited: one is white (Redfield) and another is dark yellow. Both result from mass selection. Although the cultivated and wild materials do not have a definite habitat, a desert environment is necessary. Whereas the wild varieties are generally climbers with a few guide shoots (2 to 4 m in length), there are two cultivated groups: the indeterminate shrubby varieties with short guide leaves and the indeterminate creepers with long guide leaves, which climb if they find support. The author knows only one escape variety. The secondary genetic stock is not well known: the kidney bean may be considered to be within the tertiary stock.

A good number of cultivars from which collections have been made mainly in Mexico appear to be no longer sown. It seems unlikely that many more cultivated forms will be found but it would be useful to re-examine the southern area of distribution. This examination is an example of a germplasm collection programme that has enabled a good part of the crop's variability to be saved. The two wild forms represent the major source of variation for future improvement of the species. As some plant species are threatened by overgrazing, it would be advisable to collect germplasm from Nayarit to Jalapa.

Cultivation practices

In the southern area of its distribution, the rural communities have conserved P. acutifolius, particularly because of its early maturity and reduced cultivation requirements. It is sown on the edge of maize fields, at the start of the rains to obtain the green bean and at the end of the rains to obtain the seed, or on plots around houses in virtually any period. In the northern area of its distribution (southeastern United States, northeastern Mexico), it is sown under heavy rain conditions in small fields with a favourable topography or on the edges of streams, generally alone or with some gourds and tolerated weeds. After the first heavy downpour, the land is ploughed and then sown in rows or broadcast following the second downpour. The plants are pulled up when they reach maturity and are left to dry in the sun. One week later they are trodden on a clean surface while the seeds are collected and winnowed with a basket. The seeds used to be stored in baskets or clay vessels (nowadays in tins or plastic bags), thus maintaining their germinating capacity for three years. In Campeche, to store seed for sowing, packets are made with the unopened pods and placed in contact with the smoke of embers.

Yields are estimated to be 200 to 900 kg per hectare, with wide variations depending on sowing density and rainfall. About 1000 to 2000 kg per hectare are obtained with fertilizer, with harvests of up to 4 tonnes per hectare.

Prospects for improvement

The tepary bean is considered to be a useful species for improving the kidney bean (it is not attacked by mildew or smut, Xanthomonas phaseoli), but no programmes have been carried out for improving the tepary bean itself. Unlike many leguminous vegetables, it gives an acceptable yield with less than 400 mm of annual precipitation. Its small seed size could be corrected by improving the species; the variability in colours and seed standards could also be increased. A pronounced heterosis is noticed when lines are crossed and there is a possibility of hybrid tepary beans being produced (it would be necessary to determine whether the secondary stock would make it possible to increase the flower's attractability to insects1). Some populations are susceptible to rust, oidium, mildew, root rot, leafminers, bruchids and leafhoppers. Some lines have good or excellent levels of resistance to these pests and diseases. In cultivation, the germplasm has proved susceptible to high temperatures, acidity, aluminum toxicity and common mosaic diseases.

Its potential for introduction into desert areas (the American tropics, the Sahel, the Near East, India) is considerable but it has not been exploited. For example, in July 1985, the author sent a small sample of tepary bean plants to Chincha in Peru for evaluation; in 1989 one of the tepary beans was already being sold under the name of cuarenteno in Chiclayo. In many areas its use as a cover plant or as a crop merged with millet (Pennisetum sp.), prickly pear (Opuntia sp.), mesquite (Prosopis sp.) and jojoba (Simmondsia sp.), for human or animal consumption, has not been exploited either. It should be possible to use it as a postharvest crop when temperatures are still favourable and residual humidity is low. One of the main reasons for promoting cultivation of the tepary bean is to limit the use of water in subdesert areas.

Research should be orientated towards increasing the collection of germplasm; distributing seed from gene banks to farmers; divulging information through agricultural extension services on the cultivation potential of the tepary bean in dry zones; setting up seed improvement projects; developing food technologies suited to leguminous vegetables (for example, industrial processing of proteins), which would free the farmer from market requirements; and promoting information on the methods of consumption in order to re-upgrade the use of this legume.

1No cytoplasmatic androsterility or agents re-establishing fertility have been recorded in P acutifolius.

Phaseolus lunatus

Botanical name: Phaseolus lunatus L.

Family: Fabaceae

Common names. English: butter bean, Lima bean, Burma bean, duffin bean, Rangoon bean

There are two main genetic stocks domesticated from two separate wild forms and with morphotypes from a different seed.

Common names of the small-seed cultivars (24 to 70 g per 100 seeds). Mayan: ib (Mexico [Yucatán]); patashete (Mexico [Chiapas]); ixtapacal (Guatemala [Suchitepéquez]); Spanish: sieva, comba (Colombia [Guerrero]), furuna (Mexico [Jalapa]), chilipuca (El Salvador), kedeba (Costa Rica), frijol caballero (Cuba), haba (Puerto Rico, Panama), carauta (Colombia [Atlantic]), frijol de año (Colombia [Tolima]), guaracaro (Venezuela); French: pois souche (Haiti)

The Caribbean group is made up of small, round seed material distributed in that area.

Common names of the large-seed cultivars (54 to 280 g per 100 seeds). Spanish: lima (because of its origin from the coast of Peru), torta (Colombia [Nariño, Huila], Ecuador [Imbabura, Azuay, Loja]), layo (Peru [Cajamarca]), pallar (Peru [Lambayeque, La Libertad, Lima, Ica, parts of the range]), palato (Bolivia [Chuquisacal), poroto manteca (Argentina)

Archaeological findings in Ancash, Peru, indicate that, after Lagenaria siceraria, the large-seed species were among the first to be cultivated (8 000 years ago), while the small-seed materials in Mesoamerica date back only 1 200 years. The large-seed material appeared 5 000 years ago on the coast of Peru, where they were of great nutritional and cultural value, particularly for the Mochican and Nazca peoples. Distribution of the wild form on the northern range (electrophoresis test results show that it is the ancestor of the Andean stock) suggests that domestication took place in this area and that it expanded towards the high parts of Ecuador and Colombia as well as towards the Peruvian coast and other high parts of Peru and Bolivia. Nowadays, the green seed in particular is eaten.

On the Peruvian coast, dulce de pallar, a kind of Lima bean conserve, is prepared from the dry seed. The aesthetic value of the seeds has enabled them to be used in recreation activities in peasant communities. The small-seed cultivars were domesticated from a wild form, possibly in Mesoamerica and in more recent times. The seeds are eaten dry (the Mayans of today prefer them refried) or green. In Asia the young plants or young leaves are consumed; in Madagascar they are used to prepare hay.

Among the reasons for the present marginalization of P. lunatus, apart from abandonment of the traditional diet with the rural exodus and changes in peasant customs, we should mention the presence of a cyanogenic glucoside which in some cultivars, if detoxification is omitted, may cause poisoning. Standardization in the consumption of leguminous vegetables (some varieties of common bean or cowpea) has been prejudicial to the Lima bean because of the presence of this glucoside. The small-seed cultivars, particularly under irrigation, suffer from the competition of soybean (and sometimes the cowpea because of its price). In the Peruvian Andes, Lima beans have heavy competition from the introduced lablab [Lablab purpureus (L.) Sweet] which is resistant to weevils, and the introduced pigeon pea [Cajanus cajan (L.) Mills], which is more tolerant of drought.

Botanical description

P. lunatus is a pluriannual species (except for a few modern cultivars) with epigeal germination and fibrous roots. Its ancestral forms come from low- or medium-altitude tropical deciduous forests. It is easily distinguished by its half-moon seeds (with the exception of a group of cultivars from the Caribbean that has a spherical seed). It is striated from the hilum and has: deltoid folioles; pseudoracemes with four to 12 fruit-bearing stems; small flowers, with a standard which is greenish (Mesoamerica) or purple (Andes); very small, roundish bracteoles; and smooth, falcate pods with three to six ovules. The two wild forms display marked differences but do not justify differentiated taxonomic treatment because of the considerable introgression among their genetic stocks. It is an autogamous species with an introrse stigma, but cross-pollination may exceed 32 percent.

The earliest genotypes flower 35 days after sowing and complete their cycle in around 100 days. Others may have two flowering cycles per year depending on the distribution of rainfall. In dry areas, the plants sprout from the lower part of the stem with the return of rainfall. In the majority of the traditional varieties, the guide leaves are long (3 to 6 m), indeterminate, creeping (and therefore useful as ground cover) or climbing.

The fibrous roots may attain several metres on filtering soils with deep humidity (Yucatán, coastal Peru), thus giving the plants great vegetative vigour (greater than maize) and a survival period of up to four years. In the wild populations. the seeds are dispersed through explosive dehiscence of the pods.


Figure 4. Beans: A) Phaseolus lunatus; A1) legume; A2) seed; B) P. polyanthus; B1) legume; B2) seed

Ecology and phytogeography

Although not strict, there is a certain distribution pattern of the forms. The small-seed wild form is found from Sinaloa in Mexico to Salta in Argentina, generally below 1600 m. The small-seed cultivars frequently grow at a lower altitude in the Pacific area of Mesoamerica, from Arizona in the United States to Choco on the western range of Colombia as well as the Ecuadoran coast, and from Yucatán and Colombia to Venezuela and in the Antilles. It also exists h northeastern Brazil and in Formosa, Argentina. The larger wild form is distributed in Ecuador and in the north of Peru between 320 and 2030 m. The large-seed cultivars are distributed in Peru from 50 to 2750m and in the high valleys of Chuquisaca and Cochabamba in Bolivia. Curiously, some also exist in the south of Brazil.

P. lunatus is a generally hardy species which prefers dry climates and deep soils (pH 6 to 7.2) with good drainage. Although it is true that some forms tolerate the climate of the lower tropics well, the species' exceptional altitude range should be mentioned, particularly in Peru where some forms withstand low temperatures (Table 3). P. lunatus, both cultivated and wild, is rather heliophytic.

Genetic diversity

The intraspecific variability of P. lunatus is particularly high in the groups of Siva and Gran Lima varieties and less in the Caribbean group. There are several commercial cultivars, particularly in California (for example. Henderson and Fordhook) and for domestic consumption (unripe green seeds in salads) in the United States. Relatives of the Andean wild form are P. augusti Harms, P. bolivianus Piper and P. pachyrhiozoides Harms. Of the cultivated species, the latter has the widest secondary stock.

There are numerous gene banks, mainly in Pullman in the United States (USDA), Chapingo in Mexico (INIFAP) and Palmira in Colombia (CIAT). Germplasm has been collected in order to save traditional material cultivated in several regions of the American tropics where varieties have rapidly disappeared. It could still be collected profitably in some parts of the Yucatán peninsula, northern Colombia, San Martin in Peru and in Paraguay.

In the case of wild material (particularly of the small-seed tone) many regions fall short for collecting specimens: Tamaulipas, Sinaloa, Michoacán, Oaxaca, Chiapas, Petén in Mexico, El Salvador, Nicaragua, Panama, Venezuela and easten1 Bolivia.

Cultivation practices

In the neotropical zones of America, it is very common to find from one to five P. lunatus plants in household vegetable gardens and on small plots, as it is customary for families to add a few green seeds to soups. In the Mayan Yucatán, this bean is traditionally sown as part of the slash-and-burn clearing system with maize, buul (P. vulgaris) and gourds. On the coast of Colombia, carauta is found on plots with maize, cassava and guandul. On the coast of Peru, it was frequently found broadcast on the banks of mountain streams where it absorbed the floodwaters. Similar practices may have existed in the cinteño valley in Bolivia before the introduction of the grapevine. Nowadays, in Chinca, Peru, it is sown as a commercial monoculture (white seeds) on ridges with irrigation. In many parts of the Andean range (in the dry inter-Andean valleys at 2000 m of Nariño, Colombia; Imbabura and Azuay in Ecuador; and Cajamarca in Peru) P. lunatus is frequently seen growing on old walls separating plots and roads or on landslides and slopes. The peasants thus use the spaces of least value. In other parts of Peru (Cajamarca, La Libertad), the Gran Lima types are sown around the edge of small farms. In some places, the plants behave spontaneously and cross with the wild forms that exist in the surrounding area (for example in Succhubamba, Cajamarca).

As it is sown almost individually in many family vegetable gardens. it is difficult to give figures for yield per area. Furthermore, periodic harvesting complicates the evaluation. In the shrubby forms, seed yields of 2000 kg per hectare have been recorded and, in climbing varieties, more than 3000 kg per hectare.

Prospects for improvement

Within the cultivated species, P. lunatus competes with P. coccineus through the genetic stock which is wider (primary and secondary) and differentiated into a very early form (for which there is genetic progress); it has a good rate of allogamy and heterosis has been found; consequently there are good prospects for improvement. P. lunatus' relatively late production, as well as that of the indeterminate creeping forms, may be compensated by exploiting the earlier shrubby forms. There is a wide variation in the glucoside content in the seed, and potential for improvement with types of less than 5 ppm, without any correlation with the colour of the tegument. The evaluation of cultivars to determine the glucoside content will make it possible to establish many materials in traditional areas of cultivation and consumption. Its hardiness and lengthy production may be advantages in adverse conditions where other leguminous vegetables do not prosper. The aesthetic value of the Gran Lima varieties may be considered in the development of handicrafts (which could be useful in remote parts of the Andes). The restoration of traditional dishes and uses (for example in recreation) would also contribute to the crop's promotion. The selection of varieties resistant to grub (Acanthoscelides sp.) and weevil (Apion sp.), particularly the Gran Lima, and of shrubby forms with a greater diversity of seeds (colour, shape) as well as the study of production techniques (the use of nettings, sowing on slopes, etc.) should be mentioned as research priorities.

Phaseolus polyanthus

Botanical name: Phaseolus polyanthus Greenman

Family: Fabaceae

Common names. Spanish: botil (Mexico [Chiapas]), piloya (Guatemala [Chimaltenango]), dzich (Guatemala [San Marcos]), piligüe (Guatemala [Alta Verapaz]), petaco (Colombia [Antioquía and western region]), cache (Colombia [Cauca, Huila and southern region]), matatropa (Colombia [Huila]), toda la vida (Ecuador, northern region of Peru).

The taxon P. polyanthus was recently acknowledged as a result of identification of its ancestral forms. There are no recordings of this legume on archaeological sites, in spite of the fact that the seeds found have been analysed thoroughly. The ecological conditions under which this species grows may not have been favourable for its preservation. Mention has been made of how old this crop must be in Mexico. In comparison with the wild forms and the other species, P. polyanthus is less evolved, which appears to be the result of its more recent domestication.

It has frequently been cultivated together with maize, gourds and two species of bean (P. coccineus and P. vulgaris) in Mesoamerican regions with a humid climate and at an intermediate altitude. Like the scarlet runner bean, this crop has been reduced with modification of the traditional maize field system in many parts of Mesoamerica. If peasants have to cease cultivating a species of bean, they keep the kidney bean, which generally obtains the best price. Among the other causes of its marginalization is the extension of coffee plantations and livestock rearing in its area of cultivation. As their incomes increased. peasants tended to abandon consumption of this legume. Traditionally, the green seed is preferred (either because it is easier to digest or because of its softer tegument) when the pod reaches physiological maturity and the dry seed is favoured less: it is eaten in soups. stews or even as a sweet (Amazon region).

Botanical description

Only pluriannual forms of P. polyanthus are known, which can live from two to tour years. In drier parts (for example, western Cajamarca, Peru) it tends to behave as an annual. It is easily distinguished from the other species by its epigeal germination; fibrous, fasciculate roots; inflorescences with six to 16 fruit-bearing stems; primary bracts and long, narrow bracteoles (giving the pseudoraceme the appearance of a spike); white or lilac flowers (purplish pink in the wild form); and terminal stigma. Its seed (70 to 100 g per 100 seeds for cultivated varieties and 16 to 25 g for wild forms) has a wide, elliptical hilum and the parahilum is frequently broken.

Ecology and phytogeography

P. polyanthus is distributed in intermediate altitudes (800 to 2600 m) in cool, damp climates with one dry period per year (Table 3); it has a long flowering period (two to five months) and can have two flowering and fruit-bearing periods per year if the rainy season is heavy (Colombia, Venezuela). It prefers deep, organic, damp and well-drained soils with pH 6.2 to 6.5 and it tolerates a degree of shade.

The cultivated form is found in Puebla, Veracruz, Oaxaca and Chiapas (Mexico). In Guatemala. it can be seen in Huehuetenango, San Marcos, Quezaltenango, Totonicapán, Baja and Alta Verapaz, Sololá, Chimaltenango and Sacatepéquez. It is also distributed in the upper parts of the Caribbean (Jamaica, Dominican Republic) and Costa Rica. It is cultivated in South America, where it is found in secondary vegetation, including wooded vegetation, from Mérida in Venezuela to Apurimac in Peru and in the western and central ranges of Colombia (the petaqueras of Antioquía), Ecuador (Azuay, Pichincha, Tungurahua) and northern Peru (Cajamarca, Amazon, Junín). To date, the wild form has been found only in the central-western part of Guatemala, where it is a liana that grows in the low, humid mountain forest; the possibility of it also occurring in the mountainous zone of the Jalisco-Michoacán boundary in Mexico should not be excluded.

Genetic diversity

This species is considered to be the least evolved of the cultivated Phaseolus species, hence it should have a greater potential for future development. There is little phenotypic variation (only the indeterminate climbing growth habit), including in the seeds. Normally it has orangy yellow seeds, but other colours do appear: reddish brown, bay, black and creamy white, for example. Seeds of the latter colour were found by the author in the Amazon region of Colombia and in Loja, Ecuador. It may have potential as a commercial crop in northern Peru and may compete as a plant with the caballeros (P. vulgaris with a large, round white seed), which do not produce in humid areas. Greater variation is seen in the seed where natural hybrids exist with P. coccineus (for example, in Putumayo, Colombia) and with P. vulgaris (for example in Tolima, Colombia) where colours may be combined with purple, coffee, etc. To date, there do not seem to be any properly recorded cultivars.

It is evident that P. coccineus, P. polyanthus and P. vulgaris are genetically close as a result of natural introgression among the species. However, each comes from a different and individualized ancestral form. The reason for this relationship should be found in the origin of the ancestral forms. Other species of the P. coccineus complex may also be considered to be close to the cache; the genetic stock of P. polyanthus is therefore wide.

An exact evaluation of genetic erosion in this species is difficult: in some parts of Guatemala (San Marcos, Chimaltenango) and Costa Rica, where the traditional maize field cultivation system has been modified, certain genotypes are disappearing; in others (Cauca, Tolima, Amazon region, in Colombia and Junín in Peru) it appears to extend into ruderal vegetations because peasants throw seed on roadsides and in smallholdings, etc. One farmer in Huila, Colombia, mentioned that it was the first seed that he sowed in the slash-and-burn system of Los Paez. The species' hardiness in humid environments provides food when the maize harvest is insufficient and explains its frequent presence in secondary forests in Colombia, Ecuador and northern Peru. It is even more difficult to evaluate erosion, as it is a predominantly allogamous species (although the local variation of this allogamy is not well known). However, it does seem useful to document the evolution of the native material in its areas of genetic cultivation in Mexico and Guatemala and to collect germplasm in appropriate cases. In the southern area of its distribution, where there seems to be less variation and erosion, collection would not seem to be urgent. The situation is different in the case of the wild ancestral form: its distribution area in central-western Guatemala is threatened by urbanization and agriculture (the primary forest where it grows is being cut down to set up coffee plantations). It is urgent to complete collection of germplasm and to ensure that at least some plant species are included in in situ conservation within the perimeter of natural parks. This method should also be considered for the few sites where there is natural introgression.

There are collections of this species, mainly in Chapingo in Mexico (INIFAP); Chimaltenango in Guatemala (ICTA); La Molina in Peru (INIAA); and Pullman in the United States (USDA). The widest collection is that of the CIAT in Palmira, Colombia.

Cultivation practices

The majority of the cultivation practices mentioned for the tepary bean in the high humid zones of Central America also apply to the cache bean. Although it is sown mixed with tepary beans, it frequently ripens a little earlier; separate harvesting (especially to eat it when green) is possible but is not always practiced. In the Andes it is frequent to see it in enclosures or in family vegetable gardens where it grows without any special care.

Prospects for improvement

A limiting factor appears to be the lesser digestibility of P. lunatus which has been verified in certain areas (Amazon region). The documentation of current consumption practices in peasant communities must be considered a priority before embarking on an investigation of its nutritional quality. It should be borne in mind that until the very recent past these beans were eaten several times a week. The lack of variation in seed colour is a problem which could be corrected partly with the distribution of germplasm from collections and through additional gatherings, particularly where there is introgression with P. coccineus and P. vulgaris. Variation in colour, type of seed and growth habits could be obtained through cross-breeding programmes that explore the primary and secondary genetic stock of P. polyanthus. Evaluation is still very much in its initial stage and is a priority for agrarian research. It would be very useful, since it is known that this species offers characteristics of resistance to several pests and diseases such as Ascochyta sp. (in the cool, humid parts of the Andes) and Ophiomyia phaseoli (in East Africa), respectively. There are genotypes ready for delivery to the farmer, particularly in conditions that are adverse to the kidney bean. The consumption of P. lunatus as a green seed could be recommended and recipes developed to improve preservation of the green seed. Its cultivation could also be encouraged in family vegetable gardens. Since the plant is attractive to livestock, it could be considered as a fodder crop in association with maize. In agrosilvicultural contexts (for instance in young plantations or hedges against erosion), it is possibly the best bean species to use. Its role in coffee plantations could also be considered from the point of view of fertilizing value and soil protection.

Conclusion

The bean was domesticated at a time when the current knowledge of molecular genetics and nutritional science was obviously not available to ensure selection of the material with the best evolutionary and nutritional potential. In addition to the kidney bean, four other species have been domesticated and have been maintained for thousands of years. It is not known whether the initial success of the kidney bean was due to its greater evolutionary potential compared with the other species or whether particular circumstances caused its domestication. Nor are all the reasons known for its promotion throughout the 200 years after 1492. Consequently, the germplasm collected of those species during the last 60 years, and the information relating to them, are possibly scarce in relation to what must have existed before the conquest. However, what has been able to be recovered is surprising and offers promise. In spite of all the changes that have occurred with the kidney bean since the fifteenth century, it has been difficult to modify its ecology drastically and the alterations that the latter may have suffered have had negative effects on species yield. Ought we not now give the neglected beans an opportunity?

Bibliography


Neglected Crops: 1492 from a Different Perspective. 1994. J.E. Hernándo Bermejo and J. León (eds.). Plant Production and Protection Series No. 26. FAO, Rome, Italy. p. 47-62.