Polymorphism of natural populations of Pinus halepensis Mill. in Morocco as revealed by morphological characters

In Morocco, Aleppo pine (Pinus halepensis Mill.) is the most used species in reforestation. However, no data is available about its intraspecific variation and adaptability. Morphological traits of 15 natural populations located on a North-East South-West orientation, representing its natural distribution in Morocco, were used to assess geographic variation of this species. Seed size (length, width, depth, weight and 1000 seed weight), wing length and width, cone length and width and needle length were measured for 760 trees (43–65 trees per population). A correlation matrix between morphological characters and geographic parameters (altitude, latitude north and longitude west) exhibited negative and positive correlations of seed size with the latitude and longitude parameters, respectively. Also cone characters correlated positively with altitude. Thus, populations originating from the South-West region (High Atlas and a part of Middle Atlas) showed high values of Aleppo pine characters. Factorial component analysis (FCA) and hierarchical classification of all populations lead to the formation of two major groups (South-West and North-East) containing, each one, two minor groups. Geographic pattern of Aleppo pine distribution and its adaptability in Morocco are discussed in this study. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity of wild coffee (Coffea arabica L.) using molecular markers

Genetic diversity was studied using RAPD markers among119 coffee (Coffea arabica L.) individuals representing 88 accessions derived from spontaneous and subspontaneous trees in Ethiopia, the primary centre of species diversity, six cultivars grown locally in Ethiopia, and two accessions derived from the genetic populations Typica and Bourbon, spread in the 18^th century, which gave rise to the most currently grown cultivars. Twenty-nine polymorphic fragments were used to calculate a similarity index and construct dendrograms. The Ethiopian material was separated from the Typica- and Bourbon-derived accessions and classified in four groups: one with most of the collected material from southwestern Ethiopia and three from southern and southeastern Ethiopia. Almost all detected diversity was found in the southwestern group while the southern and southeastern groups presented only 59% of identified markers. The genetic distances were low between the southwestern group and the southern and southeastern groups, and between the southwestern group and the Typica- and Bourbon-derived accessions. The cultivated coffee derived from the genetic populations Typica and Bourbon appeared little differentiated from wild coffee growing in the southwest. The results supported the hypothesis that southwestern Ethiopian coffee trees could have been introduced recently in the south and southeast. A separate analysis of the 80accessions classified in the southwestern group allowed identifying particular spontaneous- and subspontaneous-derived accessions and redundancies in the collected material from southwestern Ethiopia. RAPD markers did not detect any within-collection polymorphism except for two trees that were identified as off-types in the CATIE field genebank. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity in advanced derivatives of Brassica interspecific hybrids

Genetic diversity among the 88 entries including eighty F₄ derivatives i.e., 20 each selected from Brassica crosses viz., B. juncea × B. napus, B. juncea × B. rapa var. toria, B. juncea ×B. rapa var. yellowsarson and B. tournefortii × B. juncea, and eight parent genotypes was assessed through multivariate analysis (D² statistic). Significant differences among the family groupsas well as within the family were recorded for all the 14 characters studied. The D² analysis revealed enormous diversity among the interspecific cross derivatives. The genetic distances calculated among different Brassica species revealed that B. tournefortii had maximumdiversity with B. juncea followed by B. napus, B.rapa var. toria and B. rapa var. yellow sarson.Amongst interspecific crosses, maximum diversity was noticed indescendants of cross B. tournefortii × B. juncea followed byB. juncea × B. napus, B. juncea × B.rapa var. toria and the least in the cross B. juncea ×B. rapa var. yellow sarson. These results indicated that the derivatives selected from cross of diverse parents revealed greater diversity. The clustering pattern showed that many derivatives of the cross fell into the same cluster but in many cases in spite of common ancestry many descendants of the cross spread over different clusters. The characters, namely, plant height, secondary branches per plant, days to flowering and1000-seed weight were contributed maximum towards genetic divergence. This revised version was published online in August 2006 with corrections to the Cover Date.     

Conservation of diversity in bulk populations of barley (hordeum vulgare L.)

Summary A series of experiments was conducted to investigate the effectiveness of mass propagated heterogeneous populations (bulk populations) in preserving genetic and phenotypic diversity. Five genetically broad-based bulk populations of cultivated barley (Hordeum vulgare L.) were employed. All of them were produced originally through mass hybridization that was facilitated by male sterility. Four of these populations had a common origin, but were subsequently propagated in different North American locations. Comparisons between early and advanced generations of these bulk populations revealed loss of variability in all populations for morphological and agronomic characters and very little to none for eight isozyme characters. Populations propagated in different locations differed in levels of residual diversity. The bulk populations were less variable than a random sample of parental accessions. The rapid loss of diversity in bulk populations was considered detrimental to genetic conservation.     

Genetic diversity within commercial populations of watercress (Rorippa nasturtium-aquaticum), and between allied Brassicaceae inferred from RAPD-PCR

Commercial productivity of watercress (Rorippa nasturtium-aquaticum) can be adversely affected by the pathogenic crook-root fungus, Spongospora subterranea f.sp. nasturti, and watercress viruses. As there are no effective control measures for these diseases, attempts have been made to breed varieties resistant to the crook-root pathogen. This work has been hindered by a lack of knowledge of the genetic base of commercial watercress, and the genetic distance between watercress and allied Brassicaceae which have been identified as candidates for hybridisation programmes. We measured the diversity within these two groups using the RAPD-PCR fingerprinting technique and analysed the data by both distance methods and principal co-ordinate analysis. Little genetic diversity was found within commercial watercress populations. However, watercress formed a unique cluster genetically distinct from other Rorippa species, but equidistant to Cardamine species. It was placed closer to Barbarea verna. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic variation in the olive tree (Olea europaea L.) cultivated in Morocco

Summary Genetic variation was studied using enzyme polymorphism at 8 loci in ancient olive trees. These were being cultivated in 10 sites along a transect from North (Pre-Rif) to South (Anti-Atlas), involving the main ecological areas where the species is cultivated in Morocco. For the 328 trees studied, 16 alleles and 68 multilocus genotypes, of which one was present in more than half the individuals analysed, were detected. Eighty seven per cent of the total genetic diversity was attributable to within site variation and showed a high proportion of local genotypes. The highest values for both genotype number and heterozygosity were observed in the South of Morocco. Such high variation may be due to the partial domestication of olive material which may be derived from crosses between cultivars or between cultivars and feral or wild olive (oleaster) trees growing frequently in the Southern region. Genetic diversity in Moroccan olive, constitutes an important genetic resource which must be conserved for further breeding.     

AFLP analysis of genetic diversity within and between populations of perennial ryegrass (Lolium perenne L.)

Amplified fragment length polymorphism (AFLP) analysis has been used to measure genetic diversity in perennial ryegrass (Lolium perenne L.) and to relate intra- and interpopulation variation to breeding history. Cluster analysis of AFLP data from contrasting populations showed features consistent with the origins of these varieties. Significant differences in intrapopulation diversity were detected and partial separation of different cultivars was observed. Restricted base cultivars, derived from small numbers of foundation clones, were suitable for this type of study, allowing near complete discrimination of closely related cultivars. Analysis of bulked samples was based on the pooling of genomic DNA from 20 individuals from 6 selected populations. Cluster analysis of AFLP data from bulked samples produced a phenogram showing relationships consistent with the results of individual analysis. AFLP profiling provides an important tool for the detection and quantification of genetic variation in perennial ryegrass. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity of Brassica napus L. Germplasm from China and Europe assessed by some agronomically important characters

Summary The genetic diversity and relationships among 63 rapeseed accessions, including 34 Chinese, 22 Czech, 2 Swedish, 2 German, one French and 2 Canadian accessions, were evaluated by nine agronomically important characters in the field at Yangling, Shaanxi, China. Significant differences between Chinese and European group in plant height, setting position of the first primary branch, number of siliques of the terminal raceme, thousand seed weight and seed yield per plant were detected. There were significant variations in nine agronomic characters among the tested rapeseed accessions. Ward’s minimum variance cluster analysis based on Mahalanobis distances on the raw data of nine agronomic characters clearly separated the European accessions from the Chinese ones. However, the Chinese accessions with erucic acid free and/or low glucosinolates could not be separated from those Chinese accessions with both high erucic acid and glucosinolates. In general, cluster analysis of the 63 accessions based on the selected agronomic characters was consistent with known pedigree information and geographic origin, as well as the previous RAPD results of these accessions. The European rapeseed could be important germplasm resources for enriching the genetic background of Chinese rapeseed, and vice versa.     

Morphological variation in Astragalus hamosus L. and Coronilla scorpioides L. populations of Tunisia

Morphological variation between Astragalus hamosus and Coronillascorpioides populations was studied using local germoplasm collected in northern and central Tunisia. Twenty-one morphological traits were recorded and data were analysed using complementary statistical analysis. Considerable variation based on morphological and agronomical traits was found between populations and for both species. Pod and peduncle lengths as well as flowers number were the most discriminant variables between populations. Differences were also found for variables like seed number per pod, seed yield and dry matter production. Significant correlations were found between plant traits and the environmental parameters of the origin sites. This study revealed enough variation among populations to initiate a selection programme for pasture improvement in arid and semi-arid areas of Tunisia, where the two species are well adapted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic resources of wild cereals in Israel and vicinity. I. Phenotypic variation within and between populations of wild wheat,Triticum dicoccoides

Summary Populations of wild emmer wheat, Triticum dicoccoides, in Israel, originating from diverse habitats, and tested earlier for allozyme (Nevo et al., 1982) and disease resistance polymorphisms (Moseman et al., 1983a, 1983b; Nevo et al., 1984a, 1984b), were compared and contrasted for performance in agronomically important phenotypic traits. The traits compared involved 10 variables comparing germination, earliness, biomass and yield variables. The field experiments were conducted in 1980, 1981 and 1982 in two relatively standardized and contrasting environments: mesic (Mount Carmel, Haifa) and xeric (Acedat Farm, and Sede Boqer, in the northern Negev desert). The experimental design involved 12 population quadrangles at Avedat Farm in 1980, and rows of randomized genotypes of five populations in both Haifa and Sede Boqer in 1981 and 1982.The results indicate that the characters studied are partly genetically determined. Striking genetic variation was found between and, at least in some characters, also within populations in each site, whereas remarkable environmental variation including genetic-environmental interaction was found between the mesic and the xeric sites. We conclude that natural populations of wild emmer wheat in Israel vary not only in genetic polymorphisms of allozymes and disease resistance, but also in quantitative traits of agronomic importance. These traits are economically significant and should be conserved and utilized in wheat crop improvement.     

Genetic resources of wild cereals in Israel and vicinity. II. Phenotypic variation within and between populations of wild barley,Hordeum spontaneum

Summary Populations of wild barley, Hordeum spontaneum, in Israel, originating from diverse habitats, and tested earlier for allozyme (Nevo et al., 1979a) and disease resistance polymorphisms (Moseman et al., 1984; Nevo et al., 1984a), were compared and contrasted for performance in agronomically important phenotypic traits. The traits compared involved 10 variables comparing germination, earliness, numerical and weight variables of biomass and yield. The field experiments were conducted in 1980, 1981 and 1982 in two relatively standardized and contrasting environments: mesic (Mount Carmel, Haifa) and xeric Avedat farm, and Sede Boqer (both in the northen Negev desert). The experimental design involved 26 population quadrangles at Avedat farm (1980), and rows of randomized plants of 11 populations in both Haifa and Sede Boqer (1981 and 1982).The results indicate that the characters studied are partly genetically determined. Striking genetic variation was found between and within populations in each site, whereas remarkable environmental variation including genetic environmental interaction was found between the mesic and the xeric sites, as well as between populations and years. We conclude that natural populations of wild barley in Israel vary not only in genetic polymorphisms of allozymes and disease resistance, but also in quantitative traits of agronomie importance. These traits are economically significant and should be conserved and utilized in barley crop improvement.     

Genetic variation in South Korean natural populations of wild soybean (Glycine soja)

Summary Wild relatives are valuable genetic resources for crop improvement. Evaluating genetic variation in these species is not only important for their use in breeding programs, but will also provide information about evolution of crops. Seeds representing six natural populations were used to study the level of variation in the South Korean wild soybean. Electrophoretic assays of the seeds on horizontal slab gels were conducted to determine the genotypes of each natural plant at 35 loci in 17 isozymes and one protein. The results indicated a surprisingly high variation. The number of alleles at each locus was as high as four. Seventy two of the 94 reported alleles for the 35 loci were present in these populations. The average number of alleles per locus, 99% polymorphism and the expected heterozygosity in the total population were 2.1, 77.1% and 0.215, respectively. This amount of variation was not only higher than that reported for 857 soybean cultivars and wild soybean populations from other geographic regions, but also higher than the average for 123 self-fertilized plant species and 473 plant species of all mating systems. The high variation in the South Korean wild soybean as well as cultivated soybean indicated in this and other population genetic studies prompts us to propose that South Korea is one of the major soybean gene centers.     

Genetic diversity and taxonomic relationships within the genus Lens as revealed by allozyme polymorphism

Summary A survey of allozyme polymorphism at 11 loci was carried out on 439 accessions from the genus Lens. This comprised 153 Lens culinaris subsp. orientalis, 35 L. odemensis, 117 L. ervoides, 32 L. nigricans, 2 of a differentiated cytotype of L. nigricans and 100 landrace accessions of the cultivated lentil (L. culinaris subsp. culinaris), from 10 different countries. The aim of the survey was to determine intra-specific genetic diversity and species relationships, based on phylogenetic and phenetic analyses, particularly regarding the position of L. odemensis and the differentiated cytotype of L. nigricans. Diversity was described by three statistics. The level of diversity in the cultivated taxon was lower than in any of the wild species according to two of these statistics, the percentage of polymorphic loci and mean number of alleles per locus. For the third measure (Nei's mean genetic diversity) it was only greater than L. ervoides. Genetic diversity statistics of the wild species indicated differences in the nature of between-population genetic diversity within the different taxa. Phylogenetic analysis suggests that L. odemensis and L. ervoides evolved from a common ancestor, and L. culinaris subsp. orientalis subsequently evolved from L. odemensis. Phenetic analysis, however, places L. odemensis closer to L. culinaris subsp. orientalis than to L. ervoides. Nei's mean genetic distance of L. odemensis from both L. culinaris subsp. culinaris (0.204) and L. culinaris subsp. orientalis (0.110) was greater than the distance between them (0.062). This evidence is not conclusive in determining whether L. odemensis should retain its specific status. Further crossability studies should be carried out on a range of genotypes to assess the potential for gene flow. The evidence presented shows the differentiated cytotype of L. nigricans to be quite distinct from other L. nigricans accessions, both phenetically and phylogenetically. This indicates that the differentiated cytotype of L. nigricans may constitute a new taxon. Discriminant function analysis reveals that isozymes may be useful in validating species classification.     

Genetic diversity for agronomic and fiber traits in day-neutral accessions derived from primitive cotton germplasm

Upland cotton (Gossypium hirsutumL) is an important crop that is cultivated in warm climates through-out the world. Agronomic performance and fiber quality must continually be improved if cotton is to maintain economic viability. Primitive ancestors of cotton contain diversity for trait improvement; however, many of these accessions have a short-day flowering response (photoperiodic) and are not readily useable in breeding programs. In this study, 114 day-neutral derived primitive germplasm lines were evaluated in field trials for two years. Agronomic and fiber trait data were collected and analyzed. Variance components, genotypic values, and genotypic correlations were calculated. Genotypic effects for all traits studied made significant contributions to the phenotypic variation indicating genetic diversity among these lines. The predicted genotypic values showed a wide range of variation for agronomic and fiber traits. Weak genotypic correlations were found between yield and 2.5% span length and fiber strength, two important fiber traits. Although these day-neutral derived accessions had lower lint percentage, they had improved fiber length, strength, micronaire, and comparable yields with two commercial cultivars. Thus, these day-neutral derived accessions are sources of genetic variation that when used in breeding programs offer the potential to improve important traits and expand genetic diversity.Contribution of the USDA-ARS in cooperation with the Mississippi Agric. and Forestry Exp. Stn. Mention of trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by USDA, ARS and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Genetic diversity and relationships among Lablab purpureus genotypes evaluated using RAPD as markers

Summary Genetic variation in 40 accessions of Lablab purpureus was evaluated using random amplified polymorphic DNA as markers. A high level of genetic variation in this species was detected but this was mainly restricted to the difference between cultivated and wild forms. Of the cultivated genotypes, genetic variation among Asian collections was significantly higher than that among African collections. The three most divergent cultivated genotypes were all from Asia. Four of the five wild accessions, two from Zimbabwe and the other two from Zambia, were closely related. The other one, CPI 31113 collected from Uganda, was highly divergent. The two commercial forage varieties used in Australia, Rongai from Kenya and Highworth from India, were not very different.     

Genetic diversity of Tainan-white maize inbred lines and prediction of single cross hybrid performance using RAPD markers

To evaluate the genetic diversity of 13 maize inbred lines, and to determine the correlation between genetic distance and single cross hybrid performance, we employed the randomly amplified polymorphic DNA(RAPD)- a PCR-based technique. Six of these lines came from the Taichung population, and others derived from seven different sites. Forty different primers were used to give a total of 646 reproducible amplification products, 547 (84.7%) of them being polymorphic. Genetic divergence was determined using Jaccard's similarity coefficient, and a final dendrogram was constructed by UPGMA (unweighted pair-group method with arithmetical averages) cluster analysis in the CLUSTER procedure of the SAS system. The RAPD analysis was a useful tool in determining the extent of genetic diversity among Tainan-white maize inbred lines in the present case. Cluster analysis showed that the 13 inbred lines could be classified into distinct heterotic groups. There was no significant linear regression of grain dry weight heterosis value and mean performance of hybrids on genetic distance. And their coefficients of determination(R²) are small, so that predictive value is limited. The present results showed that the Jaccard's similarity coefficients based on RAPD data cannot be used to precisely predict the F₁ hybrids yield performance and heterosis value. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic diversity among wild sugarcane germplasm from Laos revealed with markers

A group of 35 wild Saccharum complex clones, collected in Laos(ECL), was studied for its nuclear genetic diversity by RFLP revealed by 10dispersed low copy probes. Representatives of the main germplasmdiversity, regularly used in introgression, were also included. A preliminarycharacterisation of the new clones was performed by Erianthus specificprimers. A set of the 11 ECL clones most outstanding for their diseaseresistance and vigor and basic germplasm members were also characterisedby 9 cytoplasmic probes. Nuclear diversity evidenced that ECL clonesrepresented an independent genetic pool consisting at least of 3 differentgroups. A group of bands was exclusively exhibited by ECL clones. Theoccurrence of genetic recombination among them was suggested by thepresence of the new bands in 2 or 3 clonal groups. Erianthus specificamplification was positive for 7 ECL clones from different nuclear groups.Dendrogram analysis based on cytoplasmic diversity divided genotypes into2 major cytoplasmic types comprising 5 groups. The ECL clones separatedin 2 distinct groups: one located in the same cytoplasmic type as Erianthus clones; the other one, in an intermediate position, closer to Saccharum species. Basic clones groups were consistent with theirtaxonomic classification. The diversity revealed by nuclear singlecopy/nuclear repetitive/cytoplasmic patterns of the ECL germplasmcontrasts with what is usually observed and points to an active populationevolution. Further studies needed to confirmed this hypothesis arediscussed.     

Genetic diversity in barley landraces from Syria and Jordan

Summary Single-head progenies derived from barley landraces collected along the Fertile Crescent in Syria and Jordan were evaluated for agronomic, morphological, and quality traits in a typical barley growing area in Northern Syria. A large diversity was observed both between and within collection sites, and in most cases the variation was useful for breeding purposes. Single plant progenies were identified with larger yields and more desirable expressions of agronomic characters than the original landraces. The utilization of this material in a breeding program for dry areas is discussed.     

Genetic diversity for RAPD markers between cultivated and wild accessions of Coffea arabica

Summary Random amplified polymorphic DNA (RAPD) markers have been successfully employed to analyse the genetic diversity among cultivated and subspontaneous accessions of Coffea arabica. The narrow genetic base of commercial cultivars was confirmed. On the other hand, a relatively large genetic diversity was observed within the germplasm collection demonstrating the importance of collecting missions. Results suggested an East-West differentiation in Ethiopia, the primary centre of diversification of C. arabica. The large heterosis effect reported in intergroup hybrids could be related to such genetic differentiation. RAPD method appeared to be effective in resolving genetic variations and in grouping germplasm in C. arabica.     

Analysis of genetic diversity in Agave tequilana var. Azul using RAPD markers

By federal law in Mexico, A. tequilana Weber var. Azul is the only variety of agave permitted for the production of any tequila. Our objective was to assay levels of genetic variation in field populations of A. tequilana var. Azul using randomly amplified polymorphic DNA (RAPD) markers. Ten plants were collected from each of four different fields, with two fields being located in each of two principal regions of Mexico for the cultivation of A. tequilana var. Azul. The two regions are separated geographically by approximately 100km. Genetic relationships between A. tequilana var. Azul and two other varieties of A. tequilana Weber, ‘Chato’ and ‘Siguin’, were also investigated using RAPDs. Among the three varieties, 19 decamer primers produced 130 markers, of which 20 (15.4%) were polymorphic betweenA. tequilana var. Chato and A. tequilana var. Siguin. The results of RAPD analysis suggest that A. tequilana var. Siguin is more closely related to A. tequilana var. Azul than is A. tequilana var. Chato. Among the 40 field selections of A. tequilana var. Azul, only 1 of124 RAPD products (0.8%) was polymorphic and 39 of 40 plants were completely isogenic. This is one of the lowest levels of polymorphism detected to date for the analysis of a crop species, and is proposed to be the result of the promotion of a single conserved genotype over many years due to an exclusive reliance on vegetative propagation for the production of new planting materials. The significance of these results is discussed in relation to breeding programs focused on the improvement of A. tequilana var. Azul. This revised version was published online in July 2006 with corrections to the Cover Date.