Molecular differentiation,diversity, and folk classification of “sweet” and “bitter” cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis>) in Caiçara and Caboclo management systems (Brazil)

This study focuses the inter-relationships among the men, the use, and the intra-specific cassava diversity, under the perspective of this crop evolutionary dynamics. The origin, the use and the current local management of varieties with high and low cyanogenic potential are important questions around cassava domestication. We collected 169 local varieties identified as “sweet” or “bitter” cassava by traditional farmers from Atlantic Forest and Amazon (Medium Negro River Basin), Brazil. Using a population genetics and an ethnobotany approach, the diversity and the genetic structure of cassava were evaluated. We found a total of 115 vernacular names, and in the Atlantic Forest sample the average genetic diversity (H _S = 0.654) was higher for the sweet varieties than for bitter ones (0.582). The genetic differentiation coefficient (R _ST), used to estimate the diversity among groups, was 0.057 (P < 0.001), indicating that the divergence between the two groups is low. We obtained a low correlation between the morphological and genetic distances, and the congruence was high when the ethnoclassification and the genetic structure were considered. We discuss the adaptive advantages of the sweet varieties use, the current socio-economic changes in bitter varieties use, and the ecological history of these variety groups.     

Genetic erosion of sorghum (Sorghum bicolor (L.) Moench) in the centre of diversity, Ethiopia

The Ethiopian region is characterised by a wide range of agro-climatic conditions, which accounted for the enormous resources of agro-biodiversity that exist in the country. The most important of these resources is the immense genetic diversity of the various crop plants in the country. Of these, one of the most on farm genetically diverse crops is sorghum. Since the advent of formal breeding in particular after green revolution, genetic diversity of most crops has been threatened worldwide. In order to assess on farm genetic erosion (GE), various research methodologies were employed. These were focused group interviews with 360 farmers, on farm monitoring and participation with 120 farmers, key informant interviews with 60 farmers and development agents, and semi-structured interviews with 250 farmers. Besides, diversity fairs were done with over 1200 farmers. Notwithstanding the complexity of assessing GE, it was assessed by various methods; namely, by temporal method (comparing 1960 and 2000 collections), area method, and semi-structured interview method at individual, community or wereda level and causes of varietal loss from other various perspectives. Farmers perceived GE as the reduced importance of the variety as indicated by lower proportion in the varietal portfolio. The five most important factors for varietal loss at individual farmers’ level were reduced benefit from the varieties, drought, Khat expansion, reduced land size and introduction of other food crops respectively. GE was not affected by wealth groups and ecological regions. Farmers do not make simple replacement as a strategic mechanism for genetic resources management. GE at regional level was quantified by temporal and spatial method. There was a complementation not rivalry between farmer varieties (FVs) and improved varieties (IVs). The whole process of GE is explained by three models, namely: Bioecogeographic enhanced genetic erosion model, Farmer induced genetic erosion model and Farmer-cum-bioecogeographic genetic erosion model. As aforementioned, sorghum genetic erosion behaviour is completely different from other food crops such as tetraploid wheat. The prediction in the late seventies that complete erosion of FVs by IVs by the end of the eighties, the principle of GE that competition between IVs and FVs, favours the former and results in the replacement of the latter is not valid in the context of sorghum in Ethiopia. Hence, maintenance of the on farm genetic diversity of sorghum is a reality but GE is rhetoric.     

Farmers’ Perception and Genetic Erosion of Tetraploid Wheats Landraces in Ethiopia

Assessing genetic erosion has been suggested as the first priority in any major effort to arrest loss of genetic diversity. In Ethiopia, although it is generally accepted that significant amount of genetic erosion has occurred and is still occurring, there is little data on its amount and extent. Thus, this study is conducted to quantify the extent of genetic erosion in Ethiopian tetraploid wheat landraces and to identify major causes of genetic erosion. To this end, a field survey of 126 farmers, randomly selected over five districts in eastern, south-eastern and central highlands of Ethiopia during 2001/2002 and 2002/2003 main cropping seasons was undertaken. Questioner was used to collect primary data from farmers who are potentially rich sources of information on genetic erosion at the variety level. Additional data were collected through key informant interviewing. Moreover, resampling was made from Tulo, Chiro and Harar Zuriya districts in eastern Ethiopia. Analysis of history profiles from primary and secondary data indicated a reduction in the use of local varieties over years. Triticum polonicum and T. turgidum are becoming very localized, and therefore, they are under greater threat of extinction. Using the calculation scheme: gene erosion=100%−gene integrity, i.e., the still extant landraces, genetic erosion was calculated for the three different areas where resamplings were made. Genetic erosion of 100% was observed both in T. durum and T. dicoccon in Tulo district. Likewise, genetic erosion of 85.7, 100 and 77.8%, respectively, was calculated for T. durum, T. turgidum and T. dicoccon in Chiro district. In Harar Zuriya, a genetic erosion of 88.9% for T. durum and 100% both in T. turgidum and T. dicoccon was detected. Number of farmers growing landraces of tetraploid wheats drastically decreased in all surveyed areas in the past decades. Displacement of landraces by other crops was the prominent factor for ending landrace cultivation. Farmers’ preference to yield potential and cash crops subsequently reduced the chance of maintaining landraces. Institutional factors like access to credit and the extension advice have influenced farmers’ decision regarding cultivar choice. In all surveyed areas, the most important initial source of seed of improved wheat varieties is the seed credit from the Ministry of Agriculture which uses a ‘plant now, pay later’ scheme to promote the distribution of improved varieties and fertilizers. The problem of genetic erosion through inappropriate maintenance of ex situ collections was also recognized and discussed.     

Genetic structure of quinoa (<Emphasis Type="Italic">Chenopodium quinoa</Emphasis> Willd.) from the Bolivian altiplano as revealed by RAPD markers

Quinoa (Chenopodium quinoa Willd.) is a pseudocereal originated from the Andes important for small farmers’ food security as well as for commercial production. Recently, it has been claimed that in Bolivia genetic erosion could result from the marginalization of the crop in the north and from its commercial standardization in the south. The aim of this study was to quantify the hierarchical structure of the genetic variation present in eight quinoa field populations, consisting of cultivated and weedy individuals, representative of the altiplano and interandean valleys of Bolivia. Randomly amplified polymorphic DNA markers show that quinoa has a strong population structure and a high intra-population variation. An effect of geographical structure of the populations was highlighted, due to population isolation, not simply linked to distance but more probably to climatic and orographic barriers present in the studied zone. The population structure is also reinforced by the limited seed exchanges among farmers as revealed by field interviews. This population structure appears related to three major biogeographic zones: the northern and central altiplano, the interandean valley, and the southern Salar. Intrapopulation genetic diversity was higher than that expected for a mainly autogamous species, and higher than that reported in anterior studies based on germplasm collections. These results are commented in view of current knowledge on phylogeny and reproductive biology of the species, and their implications regarding genetic resources management are discussed.     

Maintenance of Squash (<Emphasis Type="Italic">Cucurbita</Emphasis> spp.) Landrace Diversity by Farmers' Activities in Mexico

Squash (Cucurbita spp.) is a common component in traditional cropping systems in Mexico, mainly in the agroecosystem known as the “milpa”, in which squash is cultivated in association with maize (Zea mays), the main crop. Using a questionnaire, 80 farmers were interviewed about crop production and selection practices in order to understand how these factors affect genetic diversity of local squash populations. We found that the most of the farmers who cultivate squash were elderly 59.8 ± 14.5 (mean ± SD; n = 78) years old. Squash varieties in the area were exclusively locally adapted landraces, and had not been replaced by modern squash cultivars. Two cultivated squash species, C. argyrosperma ssp. argyrosperma and C. moschata, had been grown intercropped with maize by 97.5% of the interviewed farmers, but only 50.0% were still producing squash at the time of the study. Farmers recognize typical characteristics of particular varieties within each of the local cultivated squash species, and selection is directed to maintain their identity. Nearly two thirds of the farmers (62.0%) had exchanged seeds of squash for planting, a practice that serves to increase genetic variability in the populations. All of the interviewed farmers were conscious of the possible hybridization between the wild gourd (C. argyrosperma ssp. sororia) and their cultivated squash. Despite various natural and human managed factors identified as contributing to enhancement of genetic diversity in these populations, results of the study show that genetic erosion of Cucurbita is likely in the region in the near future.     

Diversity in Phenotypic Profiles in Landrace Populations of Vietnamese Rice: A Case Study of Agronomic Characters for Conserving Crop Genetic Diversity on Farm

Phenotypic variation of agronomic characters in aromatic rice (Oryza sativa L.) was analyzed in order to elucidate the genetic diversity of the populations of rice landraces. Thirteen populations in Namdinh province, in the Red River Delta of Vietnam, were studied in both of farmers fields and an experimental field. Only small differences were found in agronomic characters among the populations, including populations containing different varieties. Variations among the populations in the frequency distributions of several characters suggested different degrees of diversity among the populations even among populations with the same variety name. The phenotypic profiles of farmers fields were different from those in an experimental field suggesting the environmental differences between them. One variety cultivated in the Myloc district had different phenotypic characters from the other varieties in the Haihau district more clearly in the experimental field. Since the small phenotypic variation in each of farm might be due to the genetic drift and selection by the farmers, on farm conservation of the landraces of rice is considered to be under a force to decrease phenotypic diversity. The present study suggests that the targeting several farms with different phenotypic profiles contribute to the conservation of regional genetic diversity of the landraces of rice.     

Changes in the diversity and geographic distribution of cultivated millet (Pennisetum glaucum (L.) R. Br.) and sorghum (Sorghum bicolor (L.) Moench) varieties in Niger between 1976 and 2003

Changes in the diversity of landraces in centres of diversity of cultivated plants need to be assessed in order to monitor and conserve agrobioversity—a key-element of sustainable agriculture. This notably applies in tropical areas where factors such as increased populations, climate change and shifts in cropping systems are hypothesized to cause varietal erosion. To assess varietal erosion of staple crops in a country subjected to various anthropogenic and natural environmental changes, we carried out a study based on a comparison of the diversity of pearl millet and sorghum varieties collected in 79 villages spanning the entire cereal-growing zone of Niger over a 26 year period (1976–2003). For these two crops, the number, name and type of varieties according to important traits for farmers were considered at different spatial scales (country, region, village) at the two collection dates. The results confirmed the high diversity of millet and sorghum varieties in Niger. No erosion of varietal diversity was noted on a national scale during the period covered. Some changes were observed but were limited to the geographical distribution of certain varieties. This highlights that farmers’ management can preserve the diversity of millet and sorghum varieties in Niger despite recurrent and severe drought periods and major social changes. It also indicates that rainfed cereal cropping systems in Niger should remain to be based on millet and sorghum, while reinforcing farmers’ seed systems.     

Assessment of genetic diversity among African cassava Manihot esculenta Grantz accessions resistant to the cassava mosaic virus disease using SSR markers

A study was conducted to determine the extent of genetic diversity among African cassava (Manihot esculenta Crantz) accessions resistant to the cassava mosaic virus disease (CMD), using simple sequence repeat (SSR) markers. The accessions included a breeding stock (clone 58308), five improved lines, 62 CMD resistant and 10 CMD susceptible landraces. Genetic diversity was assessed among accessions in five cluster groups derived from UPGMA analysis on data from 18 SSR primer pairs. Average gene diversity, He, was high in all cluster groups, with an average heterozygosity of 0.591 ± 0.061. The estimator of inbreeding Fis revealed a low level of inbreeding within groups and averaged −0.262 ± 0.142. Gene diversity among all accessions was 51.4% and gene diversity within cluster groups was 46.6%, while 4.8% was due to diversity between the different cluster groups. The amount of genetic differentiation measured by Gst and Fst were 9.6% and 12.1% respectively, indicating a weak genetic structure.     

Spatial and temporal dynamics in genetic diversity in upland rice and late millet (<Emphasis Type="Italic">Pennisetum glaucum</Emphasis> (L.) R. Br.) in The Gambia

Ambiguity exists about the level of genetic diversity represented by farmer crop varieties, how it develops over time and how it relates to the diversity comprised by formal varieties. As part of an interdisciplinary technological/sociological study on farmer management of gene flow, upland rice (Oryza sativa L.) and late millet (Pennisetum glaucum (L.) R.Br.) from The Gambia were investigated for morphological and molecular variation. The goal of these analyses was to obtain insight into the level of crop genetic diversity of farmer’s materials planted in several case study villages in The Gambia. For both crops, samples were collected from villages and various research institutes. Based on variety names, different rice and millet varieties were expected to be used in different villages. In fact, there was a large overlap in genetic diversity for both crops, masked by the use of synonyms. The considerable similarity in rice genetic diversity between villages most likely results from the exchange of varieties between farmers. For millet this seems the result of development of varieties from the same gene pool. Some farmer varieties of rice, however, are apparent hybrid forms between the species O. sativa and O. glaberrima Steud., and farmer varieties in general displayed higher levels of genetic diversity than formal varieties. This indicates that, for rice, genetic diversity develops in farmers’ fields and may have potential use in formal breeding programs.     

The unappreciated ecology of landrace populations: Conservation consequences of soil seed banks in Cassava

Failure to take into account the ecological complexity of landrace populations of crop plants limits our ability to conserve their genetic resources in situ. Soil seed banks are a central feature of the ecology of landrace populations of cassava; their existence has consequences for conservation. Seedlings recruited from seed banks are incorporated by farmers into their stocks of clones of this vegetatively propagated crop, transforming pure clonality into a mixed clonal/sexual reproductive system. Soil seed banks, and farmers’ responses to them, play an important role in maintaining diversity in populations of cassava landraces. In a study combining genetic and ethnobiological approaches, we showed the following: (i) Recruitment from soil seed banks increased diversity of populations at the local scale. At the level of a field, the presence of plants issued from seeds resulted in significantly greater diversity of genotypes and phenotypes than if only individuals planted by farmers had been present. (ii) Farmers’ use of seed banks has enabled indirect ‘exchange’ of locally adapted cassava germplasm between cultural groups, without requiring that groups actually encountered one another and engaged in social exchange of cultivars. (iii) Farmers have responded to catastrophic crop failure by using seed banks to regenerate stocks of clones. This use of seed banks should enable cassava populations to respond to disasters by an increase of genetic diversity, rather than by a narrowing of the genetic base, often feared in such situations.     

RAPD and AFLP assessment of genetic variation in a landrace of pepper (Capsicum annuum L.), grown in North-West Italy

In several regions of Italy as well as other parts of southern Europe, the heterogeneity of the land, the climate and the soil favour the survival in cultivation of a large number of landraces specifically adapted to local conditions. Knowledge on the level and distribution of their genetic variation can help to develop appropriate strategies, in order to suistainably manage in situ these germplasm resources at risk of genetic erosion. C. annuum is an herbaceous diploid species and is considered to be self-pollinating, although different rates of out-crossing have been recorded. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers to assess genetic diversity within and between five populations of a landrace of Capsicum annuum L., grown in a limited area in north-west Italy and locally known as Cuneo pepper. Partitioning the genetic variation with Shannon's diversity index revealed that 41.6% occurred between and 58.4% within populations. Analogous results were obtained when the analysis was based only on RAPD or AFLP markers. However, AFLP was more reliable, since a lower range of variation was observed among primer combinations in detecting the two components of genetic variation. Notwithstanding the rather high level of within genetic variation detected, the five populations were clearly differentiated and differed in the frequency of alleles exclusive and/or present at very low frequencies. Our results show the need for accurate estimation of allele frequencies, in order to identify populations to which priority should be given for dynamic conservation of landraces.     

Perceptual selection and the unconscious selection of ‘volunteer’ seedlings in clonally propagated crops: an example with African cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) using ethnobotany and population genetics

The role of sexual reproduction in magnifying genetic diversity in clonally propagated crops is now well documented. But whereas many studies have emphasized the importance of perceptual distinctiveness and its role in arousing farmers’ curiosity towards plants with unusual morphological traits, few have considered its corollary, perceptual indistinctiveness. In this study, we investigated which factors influence farmers’ behaviours towards self-sown ‘volunteer’ seedlings of cassava (Manihot esculenta Crantz) in a cross-cultural survey in Gabon, Central Africa. Interviews revealed that farmers were seven times more likely to spare seedlings that resembled a named landrace compared to those that did not. Similarly, farmers were more likely to relax weeding pressures on cassava volunteers if they believed that volunteers were resurgences from old cuttings. The model fit significantly improved when cultural factors were accounted for, suggesting strong culture-dependent differences among communities in their perception of and attitudes towards cassava volunteers. An analysis of the structure of genetic diversity of cassava landrace populations at the community level showed that most landraces included singleton genotypes, even in villages where farmers imposed the strongest weeding pressures, suggesting that there is always some background incorporation of cassava seedlings. We show that by channelling the selective incorporation of cassava seedlings that are morphologically indistinguishable from familiar landraces, perceptual selection favors the recruitment, sometimes deliberate but more often unconscious, of new genotypes from plants germinating from seeds and contributes to balancing the disadvantages of strictly clonal propagation, while maintaining landraces within consensual combinations of perceptually distinct traits.     

Classification of elite cassava varieties (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) cultivated in Benin Republic using farmers’ knowledge,morphological traits and simple sequence repeat (SSR) markers

Cassava (Manihot esculenta Crantz) is an important food security crop or resource for poor rural communities particularly in Africa. The crop’s ability to produce high yields even under poor conditions and storability of its roots underground for longer periods or until needed makes it a model ‘food security crop’. In Benin Republic, cassava has been recognized as one of the major crop contributing towards dynamic value chains generating incomes for small-holder farmers. The crop is grown all over the country, however, the increased production are mainly recorded from far south and central parts of the country. Genetic improvement of cassava in Benin Republic is limited because of poor knowledge of genetic diversity present within the country. The main objective of this study was to assess the genetic diversity and relationships among elite cassava varieties collected from different regions of Benin using fluorescently labelled simple sequence repeat (SSR) markers and to compare the results with farmer’s knowledge and morphological traits. A total of 96 cultivars collected from major cassava growing areas such as Southern and Central Benin were classified into 24 different groups using farmers’ knowledge, while classification based on 18 morphological traits resulted in five groups. In total, sixteen SSR markers were tested for molecular analysis of the ninety-six cassava varieties. Among the sixteen, twelve SSR markers gave good banding pattern and were used to genotype the varieties. An average of 3.58 and 0.47 for number of alleles and polymorphism information content respectively was observed. The observed heterozygosity (H_o) ranged from 0.23 to 1.0 with an average of 0.66 indicating moderate level of diversity among the cultivars. Based on the proportion of shared alleles and hierarchical clustering, the 96 elite cassava varieties were classified as 74 unique varieties. Principal component analysis and analysis of molecular variance revealed no significant variation between the regions thus, explaining regular exchange of planting materials among cassava farmers across various regions. The moderate level of genetic diversity in famer’s field, revealed in the present study, is a good indication of the need for broadening the genetic base of cassava in Benin Republic and establishing a formal breeding program in the country.     

Genetic diversity of Syrian pistachio (<Emphasis Type="Italic">Pistacia vera</Emphasis> L.) varieties evaluated by AFLP markers

Pistachio (Pistacia vera L.) is a strategic nut tree species in the Middle East which holds comparative advantage over other fruit trees in view of its hardiness, income generation opportunities and benefits for the ecosystem. Yet pistachio cultivation depends on a very narrow genetic base, in spite of the existence of many varieties still marginally exploited. Syria is an important center of diversity for pistachio. A country wide ecogeographic survey in this country was carried out to determine the extent of pistachio genetic diversity and its use. As a whole, 114 accessions were collected from 37 farms to assess diversity at morphological and molecular level. Molecular evaluation was carried out using Amplified Fragment Length Polymorphism (AFLP) technique and performed using seven primer pair combinations. Results from the studies allowed the identification of 25 pistachio female varieties in Syria, some of which unique and described for the first time. Three groups of pistachio diversity were identified by cluster analysis which provides useful information about the distribution of genetic diversity in Syria for enhanced use and sustainable conservation.     

Diversity, distribution and management of yam landraces (Dioscorea spp.) in Southern Ethiopia

Yam (Dioscorea spp.) is widely grown in many parts of Ethiopia and plays a vital role in local subsistence. Nevertheless, its diversity has not been studied in detail. A survey covering 339 farm households and eight districts was conducted in the major yam growing regions of Southern Ethiopia to investigate the diversity and distribution of yam landraces using structured and semi-structured questionnaires. A total of 37 named landraces were recorded, with a range from one to six (mean 2.9) on individual farms. Farmers’ decisions regarding the number and type of landraces maintained was influenced by tolerance of the landraces to drought, their maturity time and market demand. Most landraces had limited abundance and distribution, and only a few dominant landraces were widely grown. There was also variation amongst districts with respect to diversity, distribution and abundance of the landraces found. In the majority of the localities surveyed, farmers reported a decreasing trend in the number of landraces maintained on individual farms and in the overall yam production. Besides, in those limited areas where yam production is expanding, farmers are increasingly relying on a few selected landraces that mature early. Findings of this study suggest that local farmers in Wolayita and Gamo-Gofa zones maintain considerable yam diversity that remains to be further explored for sustainable utilization and conservation of the available genetic resources.     

Analysis of genetic diversity in a sweet potato (Ipomoea batatas L.) germplasm collection from Tanzania as revealed by AFLP

Sweet potato (Ipomoea batatas L.) is the fifth most important crop in the developing countries after rice, wheat, maize and cassava. The amplified fragment length polymorphism (AFLP) method was used to study the genetic diversity and relationships of sweet potato accessions in the germplasm collection of Sokoine University of Agriculture, Morogoro and Sugarcane Research Institute, Kibaha, Tanzania. AFLP analysis of 97 sweet potato accessions using ten primer combinations gave a total of 202 clear polymorphic bands. Each one of the 97 sweet potato accessions could be distinguished based on these primer combinations. Estimates of genetic similarities were obtained by the Dice coefficient, and a final dendrogram was constructed with the un-weight pair-group method using arithmetic average. AFLP-based genetic similarity varied from 0.388 to 0.941, with a mean of 0.709. Cluster analysis using genetic similarity divided the accessions into two main groups suggesting that there are genetic relationships among the accessions. Principal Coordinate analysis confirmed the pattern of the cluster analysis. Analysis of molecular variance revealed greater variation within regions (96.19%) than among regions (3.81%). The results from the AFLP analysis revealed a relatively low genetic diversity among the germplasm accessions and the genetic distances between regions were low. A maximally diverse subset of 13 accessions capturing 97% of the molecular markers diversity was identified. We were able to detect duplicates accessions in the germplasm collection using the highly polymorphic markers obtained by AFLP, which were found to be an efficient tool to characterize the genetic diversity and relationships of sweet potato accessions in the germplasm collection in Tanzania.     

The assessment of biodiversity loss over time: wild legumes in Syria

The conservation community has been set a considerable challenge by way of the CBD (Convention on Biological Diversity) 2010 targets. This may not be achievable by 2010 as demanded by the CBD, but at least methodologies can be assessed with a view to their implementation, so that loss of biodiversity and its inherent genetic diversity can be reduced post 2010. There is therefore a need to develop and implement protocols to efficiently measure genetic erosion and to make the identification of the drivers of erosion clear enabling counter-measures to be taken. In this paper the applicability of the indirect genetic erosion threat assessment for wild populations of rare and endemic Vicia species has been investigated. The method applied was based on the scoring of 18 factors perceived to be threats in the 18 study sites in two regions of Syria. Both temporal and spatial patterns of genetic erosion were considered. The method clearly detected spatial patterns of threat, enabling discrimination between the study sites located in the two study regions. However, no significant variation among the sites within each region was detected, highlighting the restricted spatial resolution of the method. Most importantly the results were in agreement with population demographic change observed, confirmed by a highly significant correlation between the erosion threat score and the relative population size change over the last 20 years. The results confirm the great potential of indirect genetic erosion threat assessment in routine evidence-based wild plant conservation decision-making.     

Ecological stability of genetic diversity among landraces of little millet (<Emphasis Type="Italic">Panicum sumatrense</Emphasis>) in south India

Risk-prone agriculture by resource-poor tribal farmers in Kolli hills, south India is slowly giving way to commercial exploitation for paltry compensation thus eroding genetic diversity of millets. Cultivation and conservation of millets, particularly, little millet (Panicum sumatrense Roth ex Roem. et Schult.), called samai in the local language, Tamil are on the wane. Whether irregular and sparse cultivation of little millet by tribals has an impact on the current level of genetic divergence is also not clear. Therefore genetic divergence among 7 landraces and 1 check variety was evaluated based on morphometric traits at two sites over two seasons. The seven landraces formed six distinct groups with high inter-group distances. Days to maturity and flowering time contributed the most to genetic differentiation. Principal component analysis confirmed the results of divergence analysis. But a recent molecular analysis of diversity reported that the landraces were all genetically uniform and any observed diversity could be due environmental variation. An analysis of the contradictory results only emphasized the fact that lack of polymorphism need not imply lack of genetic divergence. The findings co evaluated with relevant published work highlight the value of morphometric analysis and reveal sustained genetic divergence in little millet.     

Characterization of a flint maize (Zea mays L. convar. mays) Italian landrace: I. Morpho-phenological and agronomic traits

Maize (Zea mays L.) landraces have the highest genetic variation and adaptation to the natural and anthropological environment where they have evolved. Surveying both qualitative and quantitative morphological traits of existing landraces may be useful in maintaining their genetic diversity and preserving them from genetic erosion. Our research deals with the morpho-phenological and agronomic characterization of a flint maize landrace, named 'Nostrano di Storo', still grown in an inland hilly environment in the low valley of Chiese River in Trentino, North-Eastern Italy. The majority of plants from twenty field populations proved to belong, with few exceptions (NSt2, NSt9, NSt11), to a single population. It means that the plant material long grown in this area and maintained by local farmers through yearly selection forms a single landrace within which some populations (i.e. NSt1, NSt3, NSt4, NSt7, NSt10, NSt18, NSt19, NSt20) could be considered as most representative and taken as 'core'. This is supported by the fact that the genetic variability was much higher within than between field populations: half of the plant and ear traits investigated did not show any significant difference between populations whereas all traits but two showed highly significant differences within populations. Selection carried out over the years by each farmer according to his own criteria produced little genetic differentiation within the original population. Gene flow among farmer populations, most likely occurred through both pollen dispersion to neighboring cultivated fields and seed exchange among farmers, may help to explain the low genetic differentiation. This information is useful for both planning conservation and recognizing the landrace as a unique germplasm source of specific geographic origin.     

Genetic Diversity in a Worldwide Collection of Cherimoya Cultivars

Genetic diversity of 206 cherimoya (Annona cherimola Mill.) cultivars representing the major regions of production was determined from an analysis of 23 isozyme loci. Gene diversity in cherimoya was high, although not equally distributed among countries. Peru and Ecuador, the countries of origin of this species, showed the greatest diversity, and Spain and Madeira (Portugal) showed the least, probably due to genetics bottlenecks resulting from limited introduction. Cultivars from California showed high values for several genetic diversity measures, likely due to their diverse origins. The expansion of cherimoya cultivation out the area of origin has produced a change in the apportionment of genetic diversity, with an increase in the inter-populational components, but likely without a general erosion overall.