Identification of some Benin Republic's 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.     

Yam (Dioscorea ssp.) domestication by the Nago and Fon ethnic groups in Benin

Guinea yams (Dioscorea cayenensis-rotundata complex; D. rotundata Poir. and D. cayenensis Lam.) have been described as resulting from a process of domestication of wild yams of the section Enantiophyllum by African farmers. Although currently practised by few farmers, the process of yam domestication is still on-going in Benin. In order to document the practices used and the indigenous knowledge maintained by Nago and Fon farmers, 27 villages were surveyed. In total, 57 farmers domesticating yam were identified, and 68 yams newly domesticated (or in domestication) were collected. Fon and Nago farmers domesticate yam mainly to widen the genetic basis of the existing diversity or for simple curiosity. Among the three wild yams species (D. abyssinica Hochst. ex Kunth, D. praehensilis Benth. and D. burkilliana J. Miège) used, D. praehensilis is the most important and the most exploited. Tuber of the wild yams are collected either in the bush (most often near the village) or in the forests (far from the village) during hunting. The domestication process consists of bringing into cultivation selected individuals which go through intense vegetative multiplication and selection procedures (over a lengthy but variable period of time) that induce morphological and biochemical changes in the plant mainly at the tuber level. Individuals resulting from these manipulations were found to be, either similar or identical to known landraces or completely new based on both morphological and isozyme analysis. Because it leads to some new cultivars, this process of domestication has potential in yam breeding and appears to be a strategy that could be useful to breeders, while developing a methodology for participatory breeding of yam.     

Application of random amplified polymorphic DNA markers to evaluate intraspecific genetic variation in the Elymus alaskanus complex (Poaceae)

Random amplified polymorphic DNA (RAPD) markers were used to evaluatethe levels and patterns of genetic diversity in ten Elymusalaskanus populations, which were collected from Canada, USA,Greenland and Russia. Ten arbitrarily chosen decamer primers were used in thisstudy. The results revealed high levels of variation. The mean number of allelesper locus (Ap) was 1.5, ranging from 1.4 to 1.6, the meanpercent of polymorphic loci (Pp) was 49.5%, ranging from35.1% to 64.9%, and the mean gene diversity (Hep) was0.162, varying from 0.142 to 0.262. The total variation wasH _T = 0.403. When partitioned(G _ST), 60% of the total variation was foundamong the populations. Although the genetic diversity values obtained with RAPDsare much higher than for allozymes, they are similar regarding how the geneticvariation is distributed among populations. In addition, a similar geneticpattern of population differentiation, where populations from Greenland andthe USA (violaceus and latiglumis)were clearly separated from the others (hyperarcticus,komarovii and sajanensis), wasrevealed by both the cluster and principal coordinates analyses.