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.     

Wild and indigenous cassava, <Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz diversity: An untapped genetic resource

Cassava is the most important food for poor people in the tropics. Its roots are used either fresh or in numerous processed forms. It is a shrub with tuberous adventitious roots arising from stem cutting. Wild relatives of cassava are perennial and vary in growth pattern from nearly acaulescent subshrubs to small trees. They have been used as a source of useful characters such as high protein content, apomixis, resistance to mealy bug and mosaic disease and tolerance to drought. Cultivars stem from interspecific hybrids of cassava with M. glaziovii Muell.-Arg. are cultivated now in about 4 millions hectars in Nigeria. Indigenous clones are potential source of B-carotene and lycopene.     

Comparisons of the influence of vesicular-arbuscular mycorrhiza on the productivity of hedgerow woody legumes and cassava at the top and the base of a hillslope in alley cropping systems

We investigated the influence of vesicular-arbuscular mycorrhizal (VAM) inoculation on growth and nutrient relationships in two alley-cropping trials, one at the top and the other at the base of a hillslope. Each trial involved three woody hedgerow legumes with cassava (Manihot esculenta Crantz) as the sole intercrop. The hedgerow trees at the base of the slope showed greater survival and higher leaf dry weights than those at the top of the slope, although these parameters were not affected by VAM inoculation, either at the top or the base of the slope. In contrast to survival, the uptake of nutrients, particularly P and N, was higher for inoculated than uninoculated hedgerow trees, both at the top and at the base of slope. Increases in stem and leaf biomass and the uptake of nutrients by the trees were strongly correlated with increases in P uptake, indicating that the improvements were attributable to VAM inoculation. Cassava tuber yields at the base of the slope, from inoculated or uninoculated plants, were significantly greater than the corresponding cassava yields at the top of the slope. These increases at the base of the slope compared to the top of the slope were not attributed to available soil nutrients but to greater VAM spore density. Higher available soil moisture may have been another factor. Increasing the VAM spore density of effective mycorrhiza through proper agronomic practices at the top of a slope may bring about comparable yields on different parts of the slope.     

Application of Isozyme Data in Fingerprinting Napier Grass (Pennisetum purpureum Schum.) for Germplasm Management

Sixty-four accessions of Napier grass (Pennisetum purpureum Schum.), a forage crop of tropics and subtropics, were assessed for polymorphism in isozymes and total proteins (TP). The national germplasm collection exhibited polymorphism in all the three isozymes viz., malate dehydrogenase, glutamate oxaloacetate transaminase and peroxidase (POX) besides TP profile. Though POX and TP showed comparatively higher polymorphism, the study indicated the efficiency of three-enzyme system in identifying more than 90% of the accessions. The combination of TP and three-enzyme systems provided unique isozyme/TP banding patterns for all the 64 accessions leading to development of accession specific profile/fingerprints. In Napier, which is perennial with long vegetative phase, it is difficult to discriminate germplasm accessions based only on morphology. Thus biochemical markers could be efficiently utilized to complement morphological evaluations, in maintaining identity and purity of germplasm for proper conservation and management, for better use in breeding and for proprietary reasons.     

Propagule Quantity and Quality in Traditional Makushi Farming of Cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis>): A Case Study for Understanding Domestication and Evolution of Vegetatively Propagated Crops

Modeling how crop plants evolve under domestication requires estimating among-plant variation in important parameters of the reproductive system, including fecundity – the number of propagules produced – and propagule quality. Measuring these traits poses particular problems in vegetatively propagated crop plants. Unlike seeds, vegetative propagules are not intrinsic biological entities but are prepared by farmers. Propagule number and quality are thus determined by the interaction between plant traits and how farmers prepare propagules. We conducted observations, interviews and experiments to study this interaction in cassava grown by Makushi Amerindians, examining how both sources of variation, in plant traits and in farmers’ practices, combine to determine the number and quality of propagules produced. Increased stake mass, determined mostly by stem diameter, leads to increased yield and also to increased asexual ‘fecundity’ of the resulting plant. Farmers’ practices reflect knowledge of this relationship. Diameter is the key criterion in the selection of stems for stakes. Larger diameters are preferred; when thinner stems are used, stakes are cut longer, partially compensating for reduced mass. These results suggest that conscious and unconscious selection to increase ‘fecundity’ and propagule quality in cassava would act to favor plants with thicker stems. Mean stem diameter is greater, and variation in stem diameter is lower, in little-branched plants. Selection for increased asexual ‘fecundity’ can thus have led to reduction in the degree of branching, one of the most striking differences between domesticated cassava and its wild ancestors. Measuring variation in asexual fecundity is a key step in analyzing evolution of the mixed clonal/sexual reproductive systems that characterize many vegetatively propagated crop plants.     

Spatial patterns of diversity and genetic erosion of traditional cassava (<Emphasis Type="Italic">Manihot esculenta</Emphasis> Crantz) in the Peruvian Amazon: An evaluation of socio-economic and environmental indicators

This study evaluates quantitatively the suitability of the use of site-specific socio-economic and environmental data as indicators to rapidly assess patterns of diversity and genetic erosion risk in cassava. Socio-economic data as well as farmers’ estimation of genetic erosion were collected in the study area, the Ucayali region of the Peruvian Amazon, through interviews with 285 cassava farmers in 50 communities, while diversity was assessed based on agromorphological characterization of 295 cassava accessions. Using multivariate regression analyses, 50 and 45% of the variation in respectively diversity and genetic erosion estimation could be explained by a selected set of socio-economic and environmental indicators. In both regression models four out of the total of 38 variables proved to contribute significantly (at p < 0.10 level). Additionally, the study revealed that farmers are a good direct source of information on the diversity present at community level, which can contribute to the development of methodologies to assess diversity more rapidly. The results of this study are valuable for the development of models to rapidly assess diversity dynamics in large areas.     

The effect of vesicular-arbuscular mycorrhizal inoculation on nutrient uptake and yield of alley-cropped cassava in a degraded Alfisol of southwestern Nigeria

Leaf and root (tuber) nutrient uptake patterns of cassava (Manihot esculenta Crantz) alley-cropped with gliricidia (Gliricidia sepium), leucaena (Leucaena leucocephala), and senna [(Senna (syn. Cassia) siamea] as influenced by vesicular-arbuscular mycorrhizal (VAM) inoculation in a degraded Alfisol were investigated in consecutive years. The cassava plants were mulched with fresh prunings of each hedgerow tree species at 2-month intervals in the second and third years of alley cropping. While VAM inoculation significantly influenced the root uptake of nutrients, the leaf uptake was not affected except for the uptake of P. In most cases, there was no difference in the nutrient concentration between inoculated and uninoculated plants, either in the leaf or in the root, indicating that the productivity of cassava was regulated by the amount of nutrients the roots could absorb. In spite of similar total soil N in all inoculated and uninoculated alley-cropped cassava plots and similar exchange-able soil K contents in inoculated and uninoculated alley-cropped cassava plots with leucaena and senna, greater uptake of N, P, and K and greater concentrations of K were observed in roots of inoculated alley-cropped cassava with gliricidia and leucaena than with senna. These results indicated that greater mineralization and availability of nutrients to cassava roots from prunings of nodulating gliricidia and leucaena than from non-nodulating senna may be important, particularly with efficient VAM inoculation, in these alley-cropping systems. Also, for similar nutrients in the inoculated and uninoculated cassava soils alley-cropped with each hedgerow species, VAM inoculation significantly enhanced cassava root dry weights, indicating that an effective VAM fungus can be an agent of greater nutrient uptake in a competitive environment.     

Delimitation of Amaranthus cruentus L. and Amaranthus caudatus L. using micromorphology and AFLP analysis: an application in germplasm identification

The ‘Morelos’ accessions of Amaranthus from Mexico demonstrate taxonomic ambiguity at the basic morphologic level. The main cause is the enormous morphological and genetic variation exhibited by the species in the genus. Although basic morphological criteria can be applied to herbarium specimens or germplasm collections for quick taxonomic identification, the morphological data alone can be misleading. To ascertain the taxonomic identity of the ‘Morelos’ accessions and their hypothesized species affiliation to Amaranthus caudatus or Amaranthus cruentus, we conducted a comparative analysis of phylogenetic relationships among these taxa/accessions using amplified fragment length polymorphism (AFLP) and micromorphology methods. Based on AFLP data, all the controversial ‘Morelos’ accessions can be consistently placed into a single A. cruentus species clade, which is clearly separated from the A. caudatus species clade. The AFLP-based phylogenetic relationship of ‘Morelos’ and delimitation of A. cruentus and A. caudatus are further supported by micromorphology, showing that the combination of these techniques can provide more reliable data for germplasm identification than each method used alone.     

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 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.     

化感小麦种质资源的筛选与评价

以国内外90份不同小麦为材料,采用土壤-琼脂三明治法和田间杂草调查法,对不同小麦种质资源进行化感潜力评价,筛选出具有较强化感潜力的小麦品种。土壤-琼脂三明治法测试结果表明,不同小麦品种的化感潜力存在明显差异,对莴苣根长抑制率IR在10．1％和69．1％之间;筛选出“115／青海麦”、“92L89”、“百泉3199”、“81-214”和“92H31”5个强化感潜力的小麦品种,其对莴苣根长抑制率依次为69．1％、68．5％、68．7％、69．1％和65．2％,筛选出“抗10103（80）”和“A246”2个弱化感潜力的小麦品种,抑制率IR依次为10．1％和12．2％;田间杂草调查评价和土壤-琼脂三明治法表现出相似趋势,检测结果也得到了琼脂迟播共培法的佐证,表明采用土壤-琼脂三明治法筛选化感小麦种质资源是可行的。这为小麦化感作用研究提供了重要的种质资源,也为化感小麦种质资源的筛选提供方法借鉴。     

Univariate and multivariate analysis performed on bio-agronomical traits of Cucumis melo L. germplasm

A large collection of melon (Cucumis melo L.) germplasm has been established at the Section of Genetics and Plant Breeding, Bari University (Italy). In the present work, data regarding the variation of 20 bio-agronomical traits recorded on entries and landraces collected in Albania and Apulia region (Southern Italy) are reported. The main objective of the study was to assess and describe, by means of univariate and multivariate analyses, the genetic diversity in the collection composed by genotypes classified in the Inodorus and Cantalupensis groups. The results obtained showed a large variation for all the traits examined. Furthermore, it was possible to identify valuable genotypes for future breeding programmes aimed at improving melon traits, particularly for the Inodorus group, which is an important crop in many Southern Italian sites. Genotypes of interest were especially selected for earliness and lateness, fruit shape, soluble solids content, storage time and fruit firmness.     

Verification of identities in global cacao germplasm collections

The ex situ conservation of cacao genetic resources is in the form of field genebanks. Misidentified trees though, represent a serious problem to (i) curators, who need to capture genetic diversity, and (ii) users of germplasm material, who must be certain of the identities of the accessions for proper evaluation of their results. The presence of mislabelled trees was assessed from data compiled in the International Cocoa Germplasm Database (ICGD) 2000 v4.1CD-ROM, which contains the published records of cacao accessions in global holdings. Circumstantial evidence revealed that many germplasm collections, especially those in Brazil (CEPEC), Colombia (ICA), Costa Rica (CATIE), Côte d'Ivoire, Mexico, Malaysia, Togo, Trinidad (ICG,T) and Venezuela (EEC) probably possessed misidentified material. The severity of the problem ranged from 15–44 % and is suggested as an area for immediate resolution. Based upon the morphological data provided by the ICGD CD-ROM, several accessions were highly suspect, including 'EET 19 [ECU]', 'EET 48 [ECU]', 'EET 162 [ECU]', 'ICS 1', 'ICS 6', 'ICS 43', 'ICS 89', 'ICS 100', 'IMC 67', 'PA 121 [PER]', 'POUND 7 [POU]', 'SCA 6', 'SPA 9 [COL]', 'UF 29', 'UF 613' and 'UF 667'. However, the identification of mislabelled trees should depend ultimately on molecular analysis. Hence, the use of voucher specimens for verification is forwarded and the concept of a public domain database for microsatellite analyses of germplasm holdings is raised.     

Isozyme analysis of genetic diversity in wild Sicilian populations of Brassica sect. Brassica in view of genetic resources management

In Sicily and in the small surrounding islands the section Brassica of the genus Brassica comprises five species, B. insularis Moris, B. incana Ten., B. macrocarpa Guss., B. rupestris Raf. and B. villosa Biv. These taxa represent a genetic resource as relatives of kale crops but some populations are endangered or threatened, thus isozyme analyses were performed to assess the genetic diversity degree at population and species levels in order to assist the design of conservation management programs.Eleven loci from five enzyme systems (aconitase, leucine aminopeptidase, 6-phosphogluconate dehydrogenase, phosphoglucoisomerase phosphoglucomutase) were analyzed in sixteen natural population (fifteen from Sicily, one from Calabria). Mean within-population genetic diversity was moderate (P = 41%, A = 1.54, H = 0.16). In some cases a great number of heterozygous individuals were detected, in other cases fixation index (F) deviated significantly from Hardy-Weinberg genotypic expectations.A total of 37 alleles was recognized, six of which resulted exclusive to single populations. The among-population component of the total genetic diversity (Gst mean values) for each species was 0.30–0.37, indicating genetic differentiation among populations.Among B. villosa and B. rupestris populations genetic distance values resulted rather low and they resulted high with B. incana and B. macrocarpa populations.The results are discussed with regard to the distribution of the genetic diversity level and the genetic resources management.     

Estimation of Variability of Five Enzyme Systems Among Wild and Cultivated Species of <Emphasis Type="Italic">Trifolium</Emphasis>

The genus Trifolium comprises of 290 annual and perennial species of which the species such as T. repens, T. hybridum, T. pratense, T. ambiguum, T. resupinatum, T. alexandrinum are economically important. Boundaries between species in many cases have been difficult to define because of wide range of diversity caused by primary polymorphism. Hence, inter- and intraspecies variation in Trifolium, for zymogram pattern of five enzyme system was made to work out estimate of variability for isozymic banding pattern and get an insight into the species relationship. A total of 25 species represented by 134 accessions were compared for 5 enzymes viz. peroxidase, esterase, superoxide dismutase, acid phosphatase, and glutamate oxalo acetate transaminase using starch gel electrophoresis. Forty-six types of zymograms for Est isozyme pattern were observed amounting to 4.38 estimate of variability. The estimates of variability revealed maximum variation in T. resupinatum (4.24) followed with 3.02 in T. nigrescens. Estimate of variability for superoxide dismutase ranged from 0.46 to 2.67 among species amounting to 1.08 total variability across species. A total of 28 types of glutamate oxalo acetate transaminase zymograms were observed accounting for 2.48 estimate of variability. All but one band attributed to an estimate of variability of 1.43 in the genus for ACP and 16 different types of ACP zymograms were noticed. Highest variation for ACP was observed in T. resupinatum (4.53). Estimate of variation for peroxidase was 4.83 and 51 types of zymogram were observed. The species differed markedly for zymograms. The species distributed both in temperate and tropical parts like T. resupinatum had more variability as compared to cultivated species like T. alexandrinum and T. pratense. The rich variability present among these species can provide good source of gene transfer from wild to cultivated species which otherwise have no specific zymogram and exhibit low variability. The species sharing zymogram pattern for one or more enzymes with cultivated species were considered to have affinity and can further be utilized in attempting interspecific hybridization.     

Agro-morphological diversity scenario in upland rice germplasm of Jeypore tract

The Jeypore tract of Orissa is one of the secondary centers of origin of cultivated rice. Recent exploration to that tract has resulted in a collection of 120 accessions of upland rice germplasm. They have been conserved in both National active collection and base collection centres for further utilisation as and when it will be required. Also a historical perspective on the genetical diversity of rice germplasm of the region has been highlighted. The characterization data revealed enormous morphological as well as agronomical variability among the landraces.     

Diversity of common bean (Phaseolus vulgaris L.) germplasm from Portugal

Common bean (Phaseolus vulgarisL.) is a traditional crop in Portugal, where farmers growvarieties selected and maintained by themselves. A collection of 88landraces of common bean was evaluated for 17 quantitative andqualitative traits and the biochemical marker phaseolin to displaythe degree of variation of this germplasm. Agronomic data weresubjected to cluster analysis and several groups were identified,with three groups clustering most of the landraces. Regardingphaseolin variation the C and T banding patterns are the mostfrequent ones, so the origin of the Portuguese beans is thus probablythe Andean region of South America. These results give informationabout the origin, diversity and breeding value of the Portuguesegermplasm, that could be useful to widen the genetic base ofcurrently cultivated bean varieties in Europe.     

Isozyme variation in Passiflora subgenera Tacsonia and Manicata. Relationships between cultivated and wild species

Isozyme variation was studied in 87 plants from 32 cultivated and wild accessions of banana passion fruit (P. tripartita var. mollissima, P. tripartita var. tripartita, P. tarminiana, and P. mixta), rosy passion fruit (P. cumbalensis), tin-tin (P. pinnatistipula), gulián (P. ampullacea), P. antioquensis, P. bracteosa, and P. manicata, from the Andes of Venezuela, Colombia, and Ecuador. Six polymorphic enzyme systems (IDH, PGDH, PGM, DIA, PRX, and ACP) revealed 31 zymotypes characterized by the presence or absence of 31 electromorphs. Cluster analysis separated clearly the accessions of P. tarminiana, P. tripartita, P. mixta, and P. cumbalensis from the less typical species of subgenus Tacsonia, which is consistent with morphological evidence. P. mixta showed the highest intraspecific variation and the closest affinity with P. tripartita. The accessions of these two species formed two clusters, one dominated by Colombian genotypes and the other dominated by Ecuadorian genotypes. One of the P. tripartita var. mollissima accessions clustered close to P. tarminiana accessions. The affinity between these three species is particularly interesting for conservation and use of banana passion fruit genetic resources. All the other species formed monospecific clusters.     

Assessing the Genetic Diversity in the International Cocoa Genebank,Trinidad (ICG,T) using Isozyme Electrophoresis and RAPD

Random amplified polymorphic DNA (RAPD) and isozyme electrophoresis (IE) techniques were used to estimate the level of genetic diversity in a sample of cacao germplasm existing at the International Cocoa Genebank, Trinidad. Twenty-six cocoa populations represented by 459 cocoa genotypes were analysed using IE and 22 populations represented by 353 cocoa genotypes were analysed using RAPD. Despite few differences in the classification of the populations, both techniques revealed three major groups: the indigenous trees, the cultivated Trinitario and the cultivated trees from Ecuador. Two-thirds of the partitioned diversity were found within populations and one-third between the populations, with both techniques.