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1.
We investigated the genetic variation and relationships among 35 melon landraces collected from the Xinjiang Uygur Autonomous Region in northwestern China by using 19 polymorphic simple sequence repeat markers (SSRs). A total of 55 polymorphic alleles were amplified. The number of alleles per SSR locus ranged from 2 to 5 with an average of 2.89 alleles per locus. The average gene diversity (GD) was 0.42 with a range of 0.06–0.71, and the average observed heterozygosity was 0.22 with a range of 0.06–0.97, indicating that the genetic diversity among the Xinjiang melon landraces was abundant. Genetic variation was also detected between the landrace populations in different regions in Xinjiang. The most abundant genetic diversity was observed among the landraces in Eastern Xinjiang, with the highest GD of 0.45 and PIC of 0.39. Eleven alleles (20 %) were found exclusively in the landraces from Eastern Xinjiang, and two alleles (3.6 %) were unique to the landraces from Southern and Northern Xinjiang. The genetic similarity matrix was defined on the basis of Jaccard coefficient to determine the genetic relationships among Xinjiang landraces. Cluster analysis was performed using the unweighted pair group method with arithmetic means, showing that the ‘wild Hami’ (XJ-34) landrace was distinct from the 34 other landraces that were divided into three clusters. Therefore, the genetic background of XJ-34 differed from that of the other landraces. The landraces were not precisely separated on the basis of their geographic origins, although most of these landraces were likely grouped near one another, as visualized through principal coordinate analysis. Thus, western China is one of the primary or secondary centers of melon diversity because of the relatively higher genetic variation detected among Xinjiang landraces. Except the ‘wild Hami’ landrace, Xinjiang melon landraces could be classified into two botanical varieties, namely, var. inodorus and var. cantalupensis. However, the distinction between these two genotypes was not significantly different.  相似文献   

2.
The “Sedano Nero di Trevi” (Black Celery from Trevi) is a landrace grown in Umbria (Italy) at risk of extinction. A morpho-physiological and molecular characterisation of the landrace and a detailed investigation of its cultural and cultivation context were carried out with the aim of facilitating a request for a quality mark, implement in situ (on farm) conservation schemes that are being developed in Italy and register the landrace in the European common catalogue of ‘conservation varieties’. These actions can help the landrace survive. Six farmer populations of the landrace and four élite varieties were characterised for thirteen morpho-physiological traits and nine AFLP primer combinations. The “Sedano Nero” farmer populations were better performers than élite varieties for important agronomic traits, such as yield, under the local agronomic conditions. Both morpho-physiological traits and molecular markers clearly distinguished the landrace from the élite cultivars. In addition, a structure was detected in the landrace with farmer populations being characterised by specific alleles. These results are discussed in connection with the local seed system and possible in situ conservation strategies for landraces.  相似文献   

3.
Apart from their significance in genetic conservation, barley landraces are still favoured by local farmers in low-input farming systems. They often perform more predictably under adverse conditions than modern cultivars due to local adaptation. Increased seed exchange between farmers may put adaptation of local populations of barley landraces at risk. Isozyme markers were used to investigate differentiation and infer gene flow between local populations of barley landrace Arabi Aswad in Northern Syria. Inferred gene flow decreased exponentially with geographic distance and may imply that seed exchange between farmers is limited to a regional scale and diminishes over longer distance. Gene flow seems to be a suitable index for estimating seed exchange in highly inbreeding crop species such as barley. In the future, improved mobility of farmers and extension work may facilitate seed exchange over longer distances, and consequently jeopardise preservation of locally adapted landraces in barley.  相似文献   

4.
In Nepal, in traditional rice farming systems many diverse landraces are grown in all of the rice agro-ecosystems from low to high altitude. Three case study sites were selected to represent the major rice agro-ecozones: Bara (100–150 m) for the low-altitude terai (plain); Kaski (700–1,206 m) for the mid-hill zone; and Jumla (2,200–3,000 m) for the high-hill zone. The diversity in rice varieties was compared in these three sites and nine survey villages in a series of surveys conducted in 1998, 1999 and 2006. The level and distribution of diversity on farm varied with the physical and socio-economic settings of the farming communities. The mid-hill site (Kaski) had the highest rice landrace diversity. This was adapted to the diverse agro-ecosystems found there and there was equal diversity in Kule khet (irrigated lands by seasonal canals) and Sim khet (marshy wet land). The next most diverse system was Nicha khet (irrigated lowlands) in Bara, the low-altitude site. The high-hill site (Jumla) had the lowest rice diversity. Across all sites many of the landraces were rarely grown and then only in small areas, reflecting the specialized uses to which they were put. At all sites the most common single landrace occupied less than half of the rice area. Resource-rich farmers were the more important custodians of on-farm rice varietal diversity across the sites. There was more rice diversity in favourable environments than in less favourable ones. This was true whether diversity was measured across sites or across rice domains within sites.  相似文献   

5.
Exploiting the diversity of barley landraces in Ethiopia   总被引：1，自引：0，他引：1  
The paper describes a methodology to incorporate the collection of barley landraces available in the Plant Genetic Resources Centre of Ethiopia (PGRC/E), as well as future collections, in the Ethiopian barley breeding program. Six hundred pure lines extracted from thirty Ethiopian barley landraces were evaluated and selected, along with the original populations, between 1989 and 1993. Three lines were identified which significantly outyielded the local landrace in some of the testing sites and had a higher average yield across sites and seasons. The yield of these lines was similar to the best improved variety also developed from a landrace population. Despite the relatively small number of landrace-lines (600) in the original population, the exploitation of the diversity existing within Ethiopian barley germplasm has produced in only five years promising lines for yield at low input conditions and for disease and insect resistance. Some lines had a yield potential comparable with the best breeding lines produced earlier, and one is under multiplication for release.  相似文献   

6.
In Ethiopia, barley is generally grown in two different planting seasons per year: during the long rainy season (Meher) and the short rainy season (Belg). The aim of the present study was to assess for the first time the role of this ‘two-season system’ on the structure of the genetic diversity of the Ethiopian barley landraces. We characterised 3,170 individual genotypes from 106 landrace populations using eight morphological spike traits. The diversity within population was higher in the season where barley is more important (Belg), and in general, where its cultivation is in larger plots because of weaker ‘competition’ with others crops. This indicates that barley diversity has a complex relationship with variations in the surrounding agro-ecosystem. Overall, the divergence between the two seasons was quite small (3.4%), suggesting that seed flow does not occur independently across the years within the two seasons. This would affect the amount of mutations and historic recombination that have accumulated within these populations.  相似文献   

7.
The eleven most known landraces from central and southern Italy were analysed using ISSR markers on 15 randomly chosen individuals for each landrace, with the aim of assessing genetic variation within and among landraces and possibly ascertaining their origin and genetic relationships. A total of 164 loci were observed, 128 of which (78.05%) were polymorphic. Gene diversity over all landraces was I = 0.3759. The highest within-landrace diversity was observed in samples from the Apennine ridge and for one Sicilian landrace; on the other hand, samples from the small Sicily islands were less variable. Principal Component Analysis and AMOVA allowed the discrimination of groups of landraces with higher similarity. Analyses indicate that the small Sicily islands landraces are very closely related to one another and seem to be derived from the peninsular material; moreover, they help disclose relationships among geographically close landraces. The knowledge so acquired can, therefore, contribute to elaborate strategies for increasing the economical value of élite landraces and to protect producers from frauds.  相似文献   

8.
Genetic variation present in wild and cultivated barley populations was investigated using two sources of microsatellite also known as simple sequence repeat (SSR) markers. EST-SSRs are derived from expressed sequences and genomic SSRs are isolated from genomic DNA. Genomic SSR markers detected a higher level of polymorphism than those derived from ESTs. Polymorphism information content was higher in genomic SSRs than EST-derived SSRs. This study showed that the EST-SSR markers developed in cultivated barley are polymorphic in wild and cultivated varieties and produced high quality markers. Ten of these functional markers were polymorphic across the accessions studied. EST markers indicated clearer separation between wild and cultivated barley than genomic SSRs. The EST-SSRs are a valuable source of new polymorphic markers and should be highly applicable to barley genetic resources, providing a direct estimate of functional biodiversity.  相似文献   

9.
The contribution of farmers to the creation and maintenance of genetic diversity is beginning to receive more recognition in developed countries. Although the use of landraces and historic varieties has largely disappeared in countries with industrialized agricultural systems and formal seed markets, certain varieties with particular cultural significance have been continuously cultivated by farmers and other varieties have been preserved ex situ in genebanks. Recently, associations of organic farmers have become involved in the conservation and use of landraces and historic varieties (called farmer varieties in this article) because these varieties possess agronomic and quality traits that they have not found in modern varieties. In this study, eight farmer varieties of bread wheat from Europe selected by participating farmers were evaluated in on-farm trials during 3 years of cultivation. Each variety was grown on each farm, and phenotypic changes in each variety were measured the third year in a replicated split-plot trial on each farm comparing the version of each variety the farmer had multiplied to a sample of each variety from the region of origin. All varieties, including the two modern pureline varieties used as checks, showed statistically significant phenotypic changes over 3 years of multiplication. However, the magnitude of these changes was moderate and did not call into question varietal identity or distinctness. In addition, some traits of putative agronomic and adaptive importance, such as grain weight per spike and thousand kernel weight, did not respond positively to natural selection (environmental conditions and management practices) which suggests the necessity of farmer selection to maintain and improve varietal performance.  相似文献   

10.
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.  相似文献   

11.
Recognition by the European Community of élite landraces encourages farmers to grow these and earn more than is possible by growing modern varieties. However, farmers often exercise strong selection by collecting seed from a limited number of plants which best embody a few characters of prime interest. This, in the long run, may be responsible for considerable genetic erosion. In Southern Piedmont, North-West Italy, a local landrace of pepper (Capsicum annuum L.) known as Cuneo is grown; it deserves particular attention because of its hardiness, late production and fruit quality. We used random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers to assess the effect, on genetic composition of a population, of seed sampling carried out using the selection criteria adopted by the farmer. After two reproductive cycles using selection, it was already possible to detect loss in genetic variation and a change in allele frequencies, while no significant effect was found after two cycles of random sampling. Over this period, farmer selection pressure led to disappearance of eight low-frequency alleles, while only three alleles were lost in randomly sampled populations. Our results stress the need to adopt appropriate techniques for seed sampling in order to avoid genetic erosion of local landrace gene pools.  相似文献   

12.
Ethiopia is a centre of diversity and hosts rich genetic resources of tetraploid wheats. Through time, the wheat materials were subject to genetic erosion. Closer investigation was made to assess the status of loss, and identify the possible causes by studying two districts from East Shewa. Information from primary and secondary sources was reviewed and analysed. Farmers identified 26 tetraploid wheat landraces (21 from Akaki and 17 from Ejere), which were once widely grown in the area. Of these, only six were currently available. Compared to the formerly available number of landraces, the loss of diversity in the study area was estimated to be 77%. In the Ejere locality, the loss was 100% before the launching of the on farm landrace conservation programme, and for Akaki it was 95%. Major factors that contributed to the loss include: (1) introduction and expansion of bread wheat varieties; (2) expansion of tef; (3) lack of a mechanism to re-supply seeds of tetraploid wheat landraces; (4) decline in size of landholdings; (5) changes in land use and cropping patterns; (6) lack of policy support; and (7) expansion of improved tetraploid wheat varieties. The lessons from this study underscore the importance of strengthening the local seed supply system as a prerequisite for sustaining on farm conservation of landraces. Moreover, it is necessary to initiate diversity studies focusing on the distribution and status of tetraploid wheat landraces across the country. Complementing these by molecular analyses is essential in order to assess the genetic distinctness of the landraces.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
Phenotypic diversity for agronomic characteristics was determined in an experiment with 29 landraces and 14 improved varieties of rye from the Nordic area, Germany and Poland. The accessions were scored for 12 characters. Effects of the location, year, type, and country of origin for landraces were investigated with analysis of variance. Phenotypic variations for the traits were estimated using the Shannon–Weaver diversity index. The genetic variation was high, with an average of H 0 = 0.566. The landraces from Norway, Sweden and Finland showed the highest variation, whereas the improved varieties had the lowest. The German material also had low variation but the status of this material is uncertain. The genetic diversity showed that 70% of the variation was found within the accessions. A cluster analysis was carried out to identify the relationship between the accessions. The material grouped into eight clusters, where clusters I to V included landraces from Sweden, Finland and Norway, except for cluster III, which included one improved variety from Denmark. Cluster VI comprised a single Swedish landrace from Gotland. Most of the improved varieties were in cluster VII and the last cluster contained accessions from Germany and Sweden.  相似文献   

16.
Phaseolus vulgaris L. is an important species that originated in Mesoamerica. A Mesoamerican and an Andean gene pool are usually distinguished in the domesticated forms. Many bean landraces are still cultivated in Italy and the Department of Applied Biology maintains an ex situ collection of 146 landraces. Although protection schemes are being developed in Italy, most landraces are extinct or at risk of extinction. To facilitate their conservation and use, geographical, morphological, biochemical and molecular (SSR) data were collected and analysed to estimate the diversity and the genetic structure of the collection. Data confirmed that both the Mesoamerican and the Andean gene pools were introduced in Italy and, although a distinction between the two gene pools exists, the Italian landrace diversity is clearly structured in three clusters that are not simply ascribable to the original gene pools. The observed structure appears also to be due to adaptation to the different environmental conditions determined by altitude. This was confirmed by assessing the presence of selective effects for some of the SSR used in this study. Finally, a certain extent of admixture in Italian landrace diversity suggests past (or recurring) hybridisation events among gene pools. The combined use of morphological, biochemical and molecular data clearly distinguished almost all the landraces. The data gathered here can assist landrace in situ protection schemes that are being developed in Italy, be used to register landraces in the European common catalogue of ‘conservation varieties’ for seed commercialisation and contribute to a better use of Italian common bean diversity in breeding for organic and conventional production systems.  相似文献   

17.
On-farm varietal diversity is now highest in marginal agricultural environments because, unlike the case in more favourable areas, modern varieties have not been a sufficiently attractive option for farmers to replace their landraces. However, the continued survival of landraces on farm is dependent on the continuing failure of plant breeding to provide better alternatives. Highly client-oriented breeding can produce suitable modern varieties for areas that were dominated by landraces. We examine here the case of the adoption of two upland rice varieties in three states in eastern India, Jharkhand, West Bengal and Orissa, where our surveys had confirmed low adoption of modern varieties in the upland ecosystem. The two new upland varieties were readily accepted by farmers who rapidly adopted them on large proportions of their land. On-farm diversity is maintained by the need to trade-off among varieties but once a variety with overall superiority was found this incentive was removed. The new varieties from the client-oriented breeding did not have weaknesses that farmers had to trade-off against their landraces so they were more likely to replace them. They also replaced older modern varieties. Farmers had previously maintained them along with landraces because they had to trade-off the higher yield of Kalinga III against the more stable yield of landraces or the higher yield of Vandana against the higher gain quality of the landraces. Only mean count per household could be used to test the significance of the differences between individual years. In all states, this revealed a significant reduction in landrace diversity with the adopting farmers when the addition of the two new varieties was not considered. Trends across years for mean varietal count, total count and Shannon–Wiener index showed a significant decline in Orissa, irrespective of whether the two new varieties were included in the analysis or not. In Jharkhand there was a significant decline only for mean count when the new varieties were not included. In Orissa, it was possible to test if rare landraces were as readily replaced as more common ones. Landrace replacement was unmitigated by increasing rarity yet the most rare landraces have the highest priority for genetic conservation. Some landraces were completely replaced by the farmers in the sample despite a diverse variety portfolio being a risk-reducing strategy in a region where there is a high risk of crop failure. There was little environmental heterogeneity in the marginal, drought-prone areas to slow this decline. The new varieties had an impact on the farming system because sometimes farmers brought additional upland into cultivation. They also introduced these varieties into more favourable, medium land. The strategy of releasing two new upland varieties met with some success in maintaining diversity.  相似文献   

18.
The genetic variation existing in a set of barley (Hordeum vulgare L.) landrace samples recently collected in Morocco was estimated. Two kinds of genetic markers, seed storage proteins (hordeins) and random amplified polymorphic DNA (RAPD), were used. Only six out of 31 landraces were subjected to RAPD analysis. Both kinds of markers, RAPD and storage proteins, yielded similar results, showing that the level of variation observed in Moroccan barley was high: all landraces showed variability; 808 different storage protein patterns (multilocus associations) were observed among 1897 individuals (2.32 seeds per association, on average) with an average of 43 multilocus associations per accession. In general, genetic variation within accessions was higher than between accessions. The 100 polymorphic RAPD bands generated by 21 effective primers were able to generate enough patterns to differentiate between uniform cultivars and even between individuals in variable accessions. One of the aims of this work was to compare the effectiveness of RAPD versus storage protein techniques in assessing the variability of genetic resource collections. On average hordeins were more polymorphic than RAPDs: they showed more alternatives per band on gels and a higher percentage of polymorphic bands, although RAPDs supply a higher number of bands. Although RAPD is an easy and standard technique, storage protein analysis is technically easier, cheaper and needs less sophisticated equipment. Thus, when resources are a limiting factor and considering the cost of consumables and work time, seed storage proteins must be the technique of choice for a first estimation of genetic variation in plant genetic resource collections.  相似文献   

19.
Germplasm conserved as seeds in genebanks requires regular regeneration. In this process, selection and genetic drift may cause loss of genetic diversity from accessions. In the case of selfing crops, separation of distinct lines into different accessions may be an efficient strategy to avoid these negative effects. In order to evaluate the applicability of this method for collection management, knowledge about the level of intra-accession genetic diversity is required. By means of AFLP analysis intra-accession variation was investigated in two cultivars, two landraces and two wild populations of ex situ conserved barley germplasm. In the total sample of 216 individuals analysed (36 per accession), 22 genotypes were observed based on 104 polymorphic loci. The number of genotypes detected ranged from 1 to 3 per accession, except for a Nepalese landrace that revealed 12 genotypes. An UPGMA cluster analysis grouped the genotypes unambiguously into the accession they belonged to and genotypes within accessions were generally found to be closely related. In order to determine the repeatability of the results obtained, 11 individuals belonging to 4 genotypes from the Nepalese landrace were scored for a second set of AFLP markers. Matrices of genetic distances calculated for the two AFLP datasets were found to be highly correlated (r = 0.9346, P < 0.001). Separation of genotypes into different accessions was considered a relevant option only for the Nepalese landrace. Analysis of molecular variance indicated that this accession could be well divided into 8 distinct lines. Further implications of the results for genebank practices are discussed.  相似文献   

20.
The genetic variation within and between Spanish landraces or varieties of Phaseolus vulgaris L. (common bean) and P. coccineus L. (runner bean) has been estimated by means of isozymes and random amplified polymorphic DNA (RAPD) analyses. Likewise, storage protein and amino acid content in dry seeds have been estimated. Fifteen landraces (60 accessions) of P. vulgaris and six of P. coccineus (six accessions) have been studied. Of the seven isozymatic systems analyzed only three systems and three loci showed variability in each species. Isozyme analyses revealed that genetic variability within and between landraces exist in both species. Even variability within accession was detected in some P. vulgaris landraces. Comparison of isozyme data indicated that Spanish landraces have a lower level of genetic variability than wild American materials and probably also lower than American landraces. RAPD analysis allowed for the uniquely distinguishing of all landraces. Genetic similarity among landraces, estimated by both isozymes and RAPDs, were not related with the seed morphological characters (color, size and shape) which define each variety or landrace. Variation in protein and amino acid content among landraces was also detected. The average protein content in common bean (20.48%) was similar to values previously reported in this species and higher than the average in the runner bean landraces (16.33%). In relation to the amino acid content methionine and cysteine showed the lowest values in all samples, although the content of these two amino acids varied widely among landraces.  相似文献   

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