Genetic variability of cultivated cowpea in Benin assessed by random amplified polymorphic DNA

Characterization of genetic diversity among cultivated cowpea [Vigna unguiculata (L.) Walp.] varieties is important to optimize the use of available genetic resources by farmers, local communities, researchers and breeders. Random amplified polymorphic DNA (RAPD) markers were used to evaluate the genetic diversity in 70 cowpea accessions collected throughout Benin. Nine random primers were screened on 24 accessions to assess their ability to reveal polymorphisms in cowpea and four of them were selected for use in characterizing the total sample. A total of 32 amplified bands were generated by the four primers. The number of loci detected varied from 5 to 11. RAPD profiles were analysed and amplified polymorphic DNA fragments were used to construct a dendrogram, clustering the accessions into nine groups at a similarity index of 71% based on the Unweighted Pair-Group Method using Arithmetic Averages. The genetic diversity among the cowpea cultivars investigated was large and the RAPD proved to be a useful technique to characterise it. Based on the molecular variance, the fixation index suggests a large differentiation of cowpea cultivars in Benin

Genetic variability of cultivated cowpea in Benin assessed by random amplified polymorphic DNA

Characterization of genetic diversity among cultivated cowpea [Vigna unguiculata (L.) Walp.] varieties is important to optimize the use of available genetic resources by farmers, local communities, researchersand breeders. Random amplified polymorphic DNA (RAPD) markers were used to evaluate the genetic diversity in 70 cowpea accessions collected throughout Benin. Nine random primers were screened on24 accessions to assess their ability to reveal polymorphisms in cowpea and four of them were selected for use in characterizing the total sample. A total of 32 amplified bands were generated by the fourprimers. The number of loci detected varied from 5 to 11. RAPD profiles were analysed and amplified polymorphic DNA fragments were used to construct a dendrogram, clustering the accessions into ninegroups at a similarity index of 71% based on the Unweighted Pair-Group Method using Arithmetic Averages. The genetic diversity among the cowpea cultivars investigated was large and the RAPDproved to be a useful technique to characterise it. Based on the molecular variance, the fixation index suggests a large differentiation of cowpea cultivars in Benin

Genetic variability in yam cultivars from the Guinea- Sudan zone of Benin assessed by random amplified polymorphic DNA

Yam (Dioscorea spp.) is an important food and cash crop in the Guinea-Sudan zone of Benin. The genetic diversity of about 70 cultivars of Dioscorea cayenensis/Dioscorea rotundata (Guinea yam) andabout 20 cultivars of Dioscorea alata (water yam) was analysed using random amplified polymorphic DNA (RAPD). The amplified bands revealed high polymorphism. These polymorphic DNA fragmentswere used to construct dendrograms, clustering all accessions into 18 groups: 12 for D. cayenensis/D. rotundata and six for D. alata. The analysis of molecular variance revealed highly significant variationamong species, among groups within species, and among cultivars within groups. The study showed that the genetic diversity changed along a spatial gradient. In general, there was a tendency that mostof the varieties from the north-east and north-west of the zone investigated appeared to be distinctive from the ones of the centre. However, few varieties were distributed randomly and did not reflect anyspecific relation to their zone of collection. The current study suggests that the Guinea-Sudan zone of Benin has a large gene pool of yam varieties. Yam farmers may have played a significant role in theenrichment and the maintenance of the genetic diversity of yam

Bioversity and domestication of yams in West Africa: Traditional practices leading to Dioscorea rotundata Poir.

The domestication of wild yams is still common practice in West Africa. It also offers one of the few remaining opportunities to understand how farmers use their empirical knowledge to tap the genetic resources of wild plants and create products suitable for agriculture. Yam agronomists and breeders have, until recently, focused little attention on this process of organizing and generating agrobiodiversity. This book aims to fill the gap by pooling existing knowledge on the subject. This original field offers a wealth of prospects for scientific progress at a time when scientists are becoming increasingly aware of the fact that local farmers' knowledge and practices relating to genetic resource management substantially enhances the potential for technical progress and adaptation to environmental change. The focus is deliberately only on domestication leading to Dioscorea rotundata yams, the type most widely cultivated in West Africa. Several chapters are devoted to the biodiversity of Dioscorea rotundata yams and the wild form they derive. The authors conclude by putting forward hypotheses to explain the phenotype transformations induced by domestication practices and their maintenance by vegetative propagation. Further research, especially by geneticists, is needed to confirm these hypotheses. Some are already being assessed, using the most advanced molecular markers analysis techniques, by joint teams of scientists from developed and developing countries

Yam (Dioscorea spp.) responses to the environmental variability in the Guinea Sudan zone of Benin

This study analyzed the morphological characteristics and agronomic potentials of yam varieties (Dioscorea spp.) collected across the Guinea Sudan transition zone of Benin. Dioscorea cayenensis - D. rotundata varieties were characterized as wingless; some varieties were spineless, others had few or dense, robust or thin, and short or prickled spines. There was variation in leaf shape, stem and leaf colour, tuber shapes and forking tendencies. The tuber flesh presented different colours, texture, oxidation colour, oxidation time, and ability to irritate. Dioscorea alata varieties were all spineless and showed winged stems, pentagonal or quadrangular. Various leaf and petiole colours, and tuber shapes were observed. On average, the mean Shannon-Weaver index was 0.86 for the external morphology of the tuber, 0.55 for tuber flesh characteristics, and 1.13 for stem and leaf morphology. The pooled mean yield varied between 0.89 and 3.30 kg/heap for the early maturing varieties of the D. cayenensis - D. rotundata, between 0.94 and 3.03 kg/heap for the late varieties, and ranged from 1.45 to 4.17 kg/heap for the D. alata varieties. The year effect was highly significant for variety-type group and species, and was larger than the genotypic effect. The genotype by year interaction effects were highly significant

Using isozyme polymorphism to assess genetic variation within cultivated yams (Dioscorea cayenensis/Dioscorea rotundata complex) of the Republic of Benin

Four hundred and sixty-seven accessions of cultivated Guinea yam (Dioscorea cayenensis/Dioscorea rotundatacomplex) collected from different localities of Benin Republic were analysed to study isoenzymatic variability in seven enzyme systems: aspartate aminotransferase (AAT), esterase (EST), glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (IDH), phosphoglucomutase (PGM), phosphoglucoisomerase (PGI), and shikimate dehydrogenase (SKDH) using starch gel electrophoresis. Polymorphism was observed in all of the enzyme systems and a total of 62 electromorphs of different frequency and variability patterns were recorded. Different combinations of banding patterns of these systems led to identification of 227 different cultivars within the 467 accessions analysed. For an old and vegetatively propagated crop (with a considerable number of vernacular names) such as yam, and for which a high rate of duplication is expected, the 227 cultivars were found to be good enough to be considered as the adequate number of accessions representing the diversity in the germplasm analysed. Cluster analysis (UPGMA) produced a most likely division of the 467 accessions into two groups corresponding to D. rotundata Poir. and D. cayenensis Lam., supporting the concept that the two forms of guinea yam represent different genetic entities. The different clusters formed within the white yams (D. rotundata) did not exactly conform to the known cultivar groups. Additional polymorphic enzymes are needed for an accurate isozyme-based genetic discrimination of most of the cultivar groups

Identification of some Benin Republics Guinea yam (Dioscorea cayenensis/Dioscorea rotundata complex) cultivars using Randomly Amplified Polymorphic DNA

DNA from twenty-three late maturing cultivars of Guinea yams (D. cayenensis/D. rotundata complex) from the Benin Republic that could not be separated using isozyme markers, were examined using randomly amplified polymorphic DNA (RAPD) markers with decamer primers of arbitrary sequence. All the twelve primers tested were informative and yielded 63 amplified DNA bands from which 47 (75%) were polymorphic. Although no single primer produced polymorphic bands in all cultivars, the great majority of the cultivars were separated with the combinations of polymorphic bands generated by various primers. Putative duplicates and cultivar misclassifications were identified. Many morphologically distinct cultivars were close. The dwarf cultivar Tam-Sam considered as derived from Tabane, appeared more distant from the latter than was believed. RAPD analysis was found as a practical tool for the identification of duplicates toward establishment of an accurate core collection of Guinea yams in Benin Republic and in the other countries of the African yam belt

Varietal identification key of the cultivated yams (Dioscorea cayenensis / Dioscorea rotundata complex) of Benin republic

Based upon IBPGR (IPGRI) morphologic descriptors, 560 accessions of Benin Republic's cultivated yams (Dioscorea ccayenensis/Dioscorea rotundata complex were morphologically characterized. Ninety morphotypes were identified and accessions were classified into 26 varietal groups according to their morphological similarities. To ease the varietal identification within each varietal group, a practical identification key was constructed and a general directory of the Benin Republic cultivated yams belonging to the complex dioscorea cayenensis/Dioscorea rotundata (guinea yams) was prepared