Distribution , management and diversity of the endangered Amerindian yam ( Dioscorea trifida L . )

The objective of this study was to verify the occurrence of Dioscorea trifida in Brazil and to obtain information concerning its distribution, management and diversity. Farmers from 21 communities were interviewed in the states of São Paulo, Santa Catarina and Mato Grosso. During the visits, semi-structured interviews were conducted to collect socio-economic, management and diversity data for this crop. Fifty-one collected accessions, plus two accessions obtained at local markets of Amazonas, were characterized using 12 morphological traits. Most the interviewed farmers were men (75%) with a mean age of 59.5 years. Just a few young people and labor force were available for agricultural activities, with an average of only three individuals per farm. Most farmers (56%) grew only one variety of D. trifida, although 44% had more than one variety in their fields, which aims to provide greater assurance at harvest. Many popular names were observed for D. trifida, and cará roxo (purple yam) was the name most used by farmers (43.4%). Characters referring to the tuber, such as skin and flesh color, were most relevant for the distinction of the accessions. The results of this study may collaborate to develop strategies for conservation, both ex situ and in situ, within the view of on farm conservation.


Introduction
Dioscorea is the largest and most important genus of the family Dioscoreaceae, with 644 species approximately (Govaerts et al., 2007).Among these, only 10 are considered important in human nutrition (Lebot, 2009), and in Brazil only D. alata L., D. cayenensis Lam, D. rotundata Poir., D. bulbifera L. and D. trifida L. are grown and consumed (Pedralli, 1988;Bressan et al., 2005;Veasey et al., 2010;Siqueira et al., 2014).Domesticated by pre-Columbian peoples and of Neotropical distribution, Dioscorea trifida was probably the first yam species cultivated by indigenous peoples and immigrants from Europe and Africa in the Amazon (Lebot, 2009;Bousalem et al., 2010).Although there is still controversy regarding the origin and domestication of this species and its evolutionary history is poorly documented, studies show that among the economically important yam species in Brazil, D. trifida originated in South America, specifically in areas located on the border between Brazil, Suriname, Guyana and French Guiana (Pedralli, 1992).
In Brazil, D. trifida occurs in areas of rain forests, savannas of the Planalto Central, rocky fields of the Cadeia do Espinhaço and seasonal forests adjacent to these fields (Pedralli, 2002), and has been maintained and propagated by traditional farmers in the Vale do Ribeira, São Paulo (Bressan et al., 2005), in the Baixada Cuiabana, Mato Grosso (Ferreira et al., 2010), in Manaus and its surroundings, in the channel of Rio Negro and in Belém (Lin Chau Ming, personal communication).Despite the problems related to agricultural production and lack of consumption diversification, this crop is an important food source, because its tubers have a high nutritional quality, and astringent, antimicrobial, diuretic and energizing properties, allowing its use in fighting malnutrition and for several diseases treatment such as diabetes, reducing cholesterol and convalescence (Ramos-Escudero et al., 2010).
Although the tubers are of high nutritive quality and are highly appreciated in the cuisine of several Brazilian communities, little has been observed on the cultivation of D. trifida on a commercial basis, with the crop being underutilized and most of the cultivation performed by traditional farmers for their own subsistence (Carmo, 2002).However, in some Brazilian states, such as Amazonas and Santa Catarina, the commercialization of this species seems to occur in an intensive way (Veasey et al., 2010).
Over the past decades traditional farmers have suffered strong socioeconomic pressures that have been leading towards a decrease of agricultural activities, with farmers abandoning the fields, and thus leading to a loss of genetic diversity of yam species and other crops such as cassava and sweet potato (Siqueira and Veasey, 2009;Siqueira, 2011).In this context, there is a need for studies to verify the damage caused by these pressures to the yam crop, to estimate the genetic diversity that is managed by these farmers and to develop strategies for conservation and maintenance of traditional varieties, which are an important source of genes for various desirable agronomic characteristics such as resistance to pests, pathogens and abiotic factors.
Studies related to the morphological characterization of D. trifida accessions are scarce, such as the study conducted by Bressan (2005) This study aimed to obtain information regarding the distribution, management and the morphological and nomenclature diversity of D. trifida local varieties held by small farmers in Brazil in order to assist in the development of more effective conservation strategies for the species.

Material and Methods
Between 2009 and 2010, 21 communities in nine municipalities were visited, distributed in the States of Santa Catarina, São Paulo and Mato Grosso, located between latitudes 14°43'S and 26°15'S and longitudes 44°05'W and 57°59'W (Table 1; Figure 1).During the visits interviews and previously standardized semi-structured questionnaires were made regarding the socioeconomic characteristics of the farmers, and the management and use of D. trifida varieties.Simultaneously, with the consent of the owners, yam tubers were collected, so that all the varieties grown and consumed in these locations could be sampled and maintained ex situ.Two accessions obtained in local markets of Manaus and Barcelos, in the State of Amazonas, were also used in this study for the morphological analysis.
The collected materials were planted in pots in the greenhouse, to allow a first step of multiplication and plant quarantine.Two months after planting, the plants were transplanted to the field with two replications.The spacing between rows and between plants was 2.5 m and 1.5 m, respectively.
We used 11 qualitative and one quantitative (number of leaf lobes) morphological traits to characterize the accessions (Table 2).These traits were selected from a list developed by the International Plant Genetic Resources Institute (IPGRI) and the International Institute of Tropical Agriculture (IITA), located in Ibadan, Nigeria, which includes morphological descriptors for various economically important species of the genus Dioscorea, except D. trifida (IPGRI and IITA, 1997).The characterization was performed in two plants representing each accession.Information concerning the morphological and socioeconomic data as well as those related to the handling and consumption of D. trifida were evaluated by descriptive analysis and then compared between the different study sites.

Distribution and socioeconomic aspects
A total of 53 accessions of D. trifida was collected, with 25 accessions from São Paulo State, 14 from Mato Grosso, 12 from Santa Catarina and two accessions collected in markets of Amazonas State (Table 1).D. trifida is considered an underutilized species and is maintained mainly by small and medium size farmers.Thus, a socioeconomic characterization was necessary at the time of collection in order to acquire data to assist in the profile of these farmers.Of the interviewed farmers, responsible for the maintenance of agricultural activities related to the yam cultivation, 75% were men and 25% women.The mean age was 59.5 years old (40 ≤ n ≤ 79), with 62 years for the women, on average, and 59 years for the men, on average.
Unlike the early days of agriculture, where men were responsible for hunting and fishing, and women for planting and harvesting, currently it is observed that most of those responsible for agricultural activities are male, although all family members are involved.This is because activities related to agriculture are very laborious, with a low financial return, and therefore, the cultivation of yam is characterized by low involvement of women in field activities (Tamiru et al., 2008).
Similarly, there is a reduced number of young people and labor available for agricultural activities, with only an average of three individuals per farm the amount of people involved in activities related to the cultivation of yams.As yam is a subsistence agriculture crop maintained by the family, only family members, usually over the age of 50 years, are involved in these activities.According to Carneiro (2001), this condition becomes a problem because the maintenance of family farming occurs in an endogenously way, subsided by the community, with the successor of a productive unit traditionally being a family member.Therefore, the reduction in the number of young people and scarcity of labor may result in reducing this type of agriculture over the next generations.
The productive units, where D. trifida cultivation was observed, showed swidden fields with less than two hectares (92%), with its plantation intercropped with other species, especially vegetables, in most cases.According to Miller and Nair (2006), swidden fields are of fundamental importance for the conservation of yam varieties, as well as various other crops, since a high biodiversity, with multiple purposes for the farmers, is maintained at these sites (Smith, 1996).
In relation to the varieties grown by the visited farmers, 44% said they had acquired from predecessor family members living in the collection site, the planting being carried out with tubers derived from materials obtained some decades ago and which were passed down the generations; 40% stated they grow varieties provided by neighbors and 16% did not know the origin of the material.As there is no formal system for the supply of seed tubers, varieties of D. trifida grown in these areas are kept for decades and these are exchanged between local farmers, with a low incidence of introduction of new varieties from other areas.These data corroborate the studies reported by Tamiru et al. (2008), which also noted that in Ethiopia there was no formal system for the supply of yam tubers, as well as farmers specialized in producing materials for planting.
During the collection and subsequent identification of the material in the greenhouse, we observed that sprouted tubers sometimes belonged to other species of Dioscorea, particularly D. alata (Siqueira et al., 2014).It was also observed that 56% of the farmers cultivate only one variety of D. trifida, unlike other species of vegetative propagation, such as cassava (Manihot esculenta), potato (Solanum tuberosum), sweet potato (Ipomoea batatas) (Brush et al., 1981;Salick et al., 1997;Sambatti et al., 2001;Emperaire and Peroni, 2007;Amorozo, 2008;Veasey et al., 2008), where it is customary to keep two or more varieties in the same farm.This decrease in the number of yam varieties maintained by farmers is worrisome because it is directly related to the loss of genetic resources and the process of genetic erosion.However, in general, we found several varieties of D. trifida maintained by farmers located in the study areas, which characterizes the type of agriculture practiced in the tropics, where several crop species or varieties of the same species are kept in rural farms by small and medium farmers (Clawson, 1985;Brush, 1995), in response to economic, social, cultural and natural factors (Cox and Wood, 1999).
Moreover, it was also observed that 44% of farmers plant more than one variety of D. trifida.This procedure aims to give greater assurance of harvest, because if some biotic and abiotic stress may interfere with planting, all varieties are hardly affected in the same intensity, thus increasing the probability of obtaining a production that guarantees at least the family sustainability during adverse conditions.
The loss of genetic resources was also observed when 96% of the farmers claimed to have planted yam varieties that are no longer planted in the property.The main reasons listed by the farmers were abandoning the fields in order to obtain employment in urban areas, thus ensuring a source of income to support their family; changes in the physicochemical conditions of the soil, leading to the emergence of diseases in the crop, and consequently the total loss of the crop; preference of a variety over others; reduction of manpower available to carry out the activities of preparation, planting and harvesting; poor land distribution, heavily reducing the area available for agricultural activities; lack of information regarding the proper management of the crop such as diseases and pests management, allowing large losses of tubers at harvest time; as well as increased production costs, low returns and lack of financial incentive to encourage the practice of family agriculture.
When farmers continue their activities in the field and keep the varieties of D. trifida in successive cycles of planting and harvesting, they perform several agricultural practices in order to increase the production of tubers.Among these practices, we observed the use of herbicides and organic or chemical fertilizers.However, significant differences in the mode and frequency of application of these inputs among the visited areas were found, where only farmers in Santa Catarina reported using some type of agricultural implement.This fact is relevant because we noticed that farmers in Santa Catarina are better prepared in terms of management given to the yam cultivation, which justifies the production of up to 2,500 kg of yam obtained in some properties with an area above 2 ha, the highest production found among the areas visited.This production is also related to the fact that the tubers of D. trifida are greatly appreciated by producers and consumers in the region, rather than tubers of D. alata and D. cayenensis, species of greatest economic impact in Brazil.Also, tubers of D. trifida were found being sold in a local supermarket, as well as being served in a typical restaurant of the region (Veasey et al., 2010).This species also has a commercial interest in the Amazon, being the main species of the genus Dioscorea sold in local markets (Lin Chau Ming, personal communication), such as the two accessions of the Amazon evaluated in this study.
As yam is considered an underutilized and subsistence crop, it is quite remarkable the lack of information related to its management and potential use, as emphasized by the farmers themselves, as well as the delay in the processing of yams in Brazil.These factors are reflections of a malfunction of the activities related to agricultural production and also lack of consumption diversification (Chu and Figueiredo-Ribeiro, 1991).
In other parts of the world, such as Africa and Asia, although substantial consumption diversification occurs, especially through the use of significant industrial or homemade yams products, the technological level is low and the products produced do not exceed the boundaries due to poor quality, being used only for local consumption or at a regional level.Santos (1996) stated that for the yam cultivation to reach high yields, it requires favorable climate conditions during the vegetative and reproductive cycle, especially adequate availability of light and water.However, the most limiting factors for yam cultivation are associated with low natural fertility of the soil used and improper management directly related to the small family and traditional agriculture (Chu and Figueiredo-Ribeiro, 1991).Thus, the availability of yam for industrialization in Brazil is not very significant because there is no definition of the types of products most recommended to then select varieties appropriate for each situation or market requirement.Therefore, the local interest of the farmers themselves is the main factor of selection and the driving force for the maintenance of yam varieties, especially D. trifida, whose cultivation and maintenance are performed exclusively by Brazilian farmers and some other Latin American countries such as Suriname and French Guiana (Bousalem et al., 2010).

Folk names and morphological characterization
The yam varieties found under cultivation are given different names by the local communities, which consider a combination of morphological, sensory and ecological adaptation to classify them, and perhaps these are the main criteria used to select varieties that are maintained over time (Tamiru et al., 2008).Contrary to what Stephens (2009) claims, where cará doce (sweet yam) is the only name given to D. trifida in Brazil, in this study we found that, among the folk names attributed to the species, the most mentioned was cará roxo (purple yam) (43.4% of the sampled units), followed by cará (yam) (13.2%), cará branco (white yam) (9.4%), and cará mimoso (delicate yam) (7.6%).There was also a regionalization of these names, where cará roxo was assigned to the species by the farmers in São Paulo, Mato Grosso and Amazonas, cará in Santa Catarina and Amazonas, cará branco in São Paulo and Mato Grosso, and cará mimoso only in Santa Catarina.Besides these, several other names for the species were found, but in low frequencies (Table 3).
From the morphological characterization, we found that all accessions of D. trifida showed green petioles with brown pigment; polygonal winged stem, a specific feature of climbing plants, because the presence of membranous wings on the stem facilitates their attachment during growth; absence of spines, unlike D. cayenensis and D. rotundata, widely cultivated species, especially in the northeastern and southeastern Brazil (Veasey et al., 2010); counterclockwise twining direction, exclusive of the Dioscorea species of Macrogynodium section, in which D. trifida is the only economically important species (Lebot, 2009); and underground tubers, like most species of the genus Dioscorea.
All accessions showed lobed leaves and most accessions presented alternate leaves with five lobes, except for accessions 40 and 41 collected in Acorizal, Mato Grosso, who showed only three lobes (Figure 2a and 2b).These could belong to another Dioscorea species, however due to its high morphological similarity to the other accessions, most probably these two accessions are products of gene mutation related to number of lobes.
Most accessions showed green stems with purple pigments, except for accessions 01, 02, 03, 07, 09, 10 and 14, collected in Ubatuba, São Paulo, and accessions 48 and 50, collected in Rosário do Oeste, Mato Grosso, which showed green stems with a brown pigmentation.Bressan (2005) concluded that the cultural unit, which is the community, have a great influence over the morphological characters, since farmers grow varieties with similar morphological aspects.The most important traits for the accessions differentiation were those related to the tuber, especially the skin and flesh colors (Figures 2c, 2d, 2e and 3).We found that 68% of the accessions had brown skin and 32% yellow skin.As to the flesh color, 42% of the accessions showed white flesh, 24% purple flesh and 34% showed flesh color of a mixture of several tonalities of white and purple, especially the accessions collected in Ubatuba, SP (Figure 2d).Characteristics related to the tubers are usually responsible for the names given to the different yam varieties by farmers, such as cará roxo (purple yam), cará branco (white yam), among others.
Because it is a vegetative propagation species and maintained primarily by family farms, some degree of homogeneity is expected among these varieties, as indicated by morphological characterization, although variations between them have been observed.However, the exchange of tubers among farmers is common practice in traditional communities.In many cases, there is an intense exchange of tubers from neighboring communities in an open and dynamic system, where local networks promote the planting of varieties in larger and more heterogeneous environments, often resulting in long-distance travelling, even among municipalities (Tesfaye and Lüdders, 2003).We conclude from this study that D. trifida is grown and consumed by traditional communities in the States of São Paulo, Santa Catarina and Mato Grosso, and is commercialized in the States of Amazonas.In most of these communities there is no formal system for the supply of seed tubers, with tubers exchange occurring among local farmers, and, consequently, a low rate of introduction of new varieties from other areas is observed.
Deficiency and lack of information related to management, potential uses and yam industrialization in Brazil are a reflection of inadequate functioning of the activities related to agricultural production and lack of consumption diversification, both caused by the lack of political and financial support for the maintenance of a production system, processing and marketing of tubers.
Given the importance of this crop and the socioeconomic context in which D. trifida cultivation is inserted, there is an urgent need to detect the genetic diversity of the species held by Brazilian farmers, to facilitate their preservation, as well as their use in breeding programs.Studies that relate the problems faced by the yam crop may enhance the role that this crop plays in food security and ensure the ongoing maintenance of yam diversity through an increased use of varieties available.
, assessing 25 local varieties of D. trifida from the Vale do Ribeira, São Paulo.Therefore, any information on the morphology of the species is important to aid to their conservation and maintenance.Based on morphological characters, Melo Filho et al. (2000) classified 11 accessions of the yam germplasm collection of the Universidade Federal Rural de Pernambuco (UFRPE), Brazil, while Mignouna et al. (2002) characterized 45 yam accessions of D. cayenensis/D.rotundata collected in Cameroon, Africa, and Hasan et al. (2008) evaluated the morphological variation among 70 accessions of D. alata from Malaysia.
/presence of wings in the stem 9. Number of lobes 4. Absence/presence of spines in the stem 10.Absence/presence of underground tubers 5. Twining direction 11.Tuber skin color 6.Stem shape 12. Tuber flesh color

Figure 2 .
Figure 2. Morphological aspects of leaves and tubers of Dioscorea trifida collected in Brazil.a) leaves with three lobes; b) leaves with five lobes; c) tubers with white flesh; d) tubers with white and purple flesh; e) tuber with purple flesh.

Figure 3 .
Figure 3. Frequencies for skin and flesh color of Dioscorea trifida tubers collected in Brazil.
Figure 1.Collection sites of Dioscorea trifida in Brazil.Accession numbers are identified in Table1.

Table 2 .
Morphological traits used for characterization of the Dioscorea trifida accessions collected in Brazil.

Table 3 .
Folk names for Dioscorea trifida given by farmers in the States of Mato Grosso, Santa Catarina, São Paulo and Amazonas, Brazil.