Response to root-knot nematodes of a germplasm collection of red clover and related species

A germplasm collection of red clover (Trifolium pratense L.) and seven related species was evaluated in greenhouse tests for resistance to Meloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood, and M. Javanica (Treub) Chitwood. Plants were rated for root galling severity and nematode egg production at eight weeks after inoculation with 1500 nematode eggs. A resistance index, RI = (gall₂; + egg₂;), was generated to assess the plants' reaction to nematode infection as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, or highly susceptible. More than 98% of red clover accessions were intermediately to highly susceptible to all four root-knot nematode species. Only one accession, PI 271627 introduced from India, had a moderate resistance level to the four nematodes tested. About one third of the T. medium accessions were resistant or highly resistant to M. arenaria, M. incognita, and M. javanica whereas more than 50% of the T. alpestre accessions were highly resistant or immune to all four nematodes species. Genetic factors for resistance to root-knot nematode could be introduced into T. pratense through interspecific hybridization with T. medium and/or T. alpestre     

Resistance to Meloidogyne javanica in wild Arachis species*

The root-knot nematode, Meloidogyne javanica Race 3 is an important nematode parasite of groundnut. Greenhouse evaluation of 184 accessions of 33 wild Arachis spp. five interspecific derivatives, 18 groundnut cultivars for root damage (galls formed by nematode) and nematode reproduction demonstrated that resistance to the nematode is available in the genepool of wild Arachis spp. Seven accessions, ICG 8952 (Arachis helodes), ICC 13211 (A. sylvestris), ICG 13224 (A. kretscmeri), ICG 13231 (Arachis sp.), ICG 14862 (A. kuhlmannii), ICG 14868 (A. stenosperma), and ICG 14915 (A. sylvestris) were highly resistant to nematode reproduction and root damage. There was no gall and eggmass formation on any plant of these accessions. Thirty-three accessions were resistant and 14 were moderately resistant. All the tested accessions of A. monticola, A. benensis, A. ipaensis, A. hoehnei, A. kempff-mercadoi, A. valida, A. chiquitana, A. rigonii, A. vallsii, A. dardani, A. paraguariensis, A. triseminata, interspecific derivatives, and groundnut cultivars were susceptible. The possible use of resistance sources in the breeding program is discussed.     

Pattern analysis of the diversity of morphological plant attributes and herbage yield in a world collection of white clover (trifolium repens L.) germplasm characterised in a summer moisture stress environment of Australia

Information on the variation available for different plant attributes has enabled germplasm collections to be effectively utilised in plant breeding. A world sourced collection of white clover germplasm has been developed at the White Clover Resource Centre at Glen Innes, New South Wales. This collection of 439 accessions was characterised under field conditions as a preliminary study of the genotypic variation for morphological attributes; stolon density, stolon branching, number of nodes, number of rooted nodes, stolon thickness, internode length, leaf length, plant height and plant spread, together with seasonal herbage yield. Characterisation was conducted on different batches of germplasm (subsets of accessions taken from the complete collection) over a period of five years. Inclusion of two check cultivars, Haifa and Huia, in each batch enabled adjustment of the characterisation data for year effects and attribute-by-year interaction effects. The component of variance for seasonal herbage yield among batches was large relative to that for accessions. Accession-by-experiment and accession-by-season interactions for herbage yield were not detected. Accession mean repeatability for herbage yield across seasons was intermediate (0.453). The components of genotypic variance among accessions for all attributes, except plant height, were larger than their respective standard errors. The estimates of accession mean repeatability for the attributes ranged from low (0.277 for plant height) to intermediate (0.544 for internode length).Multivariate techniques of clustering and ordination were used to investigate the diversity present among the accessions in the collection. Both cluster analysis and principal component analysis suggested that seven groups of accessions existed. It was also proposed from the pattern analysis results that accessions from a group characterised by large leaves, tall plants and thick stolons could be crossed with accessions from a group that had above average stolon density and stolon branching. This material could produce breeding populations to be used in recurrent selection for the development of white clover cultivars for dryland summer moisture stress environments in Australia. The germplasm collection was also found to be deficient in genotypes with high stolon density, high number of branches, high number of rooted nodes and large leaves. This warrants addition of new germplasm accessions possessing these characteristics to the present germplasm collection.     

Characterisation of white clover populations collected from the Caucasus and high altitude regions of eastern Turkey

White clover populations collected from the Caucasus region and eastern Turkey were compared with seven white clover cultivars in a moist, lowland, highly fertile environment. The Caucasus collection came from 15 sites below 1000 m and 19 sites above 1000 m; all seven sites in Turkey were above 1000 m. The populations were generally small leaved and except for those from low altitude sites in Dagestan and Azerbaijan populations were acyanogenic. None of the collected populations were significantly higher yielding than Grassland Huia in any season. However, several populations from the Caucasus were higher yielding than Kent Wild White and similar to that of Grassland Tahora. Survival was poor with only four populations having more than 50% of plants surviving after 18 months in this environment. High altitude Caucasus populations were earlier flowering than low altitude populations, an adaptation to allow adequate seed set.There was a negative relationship between altitude of population origin and proportion of cyanogenic plants; and between altitude and both leaf size and canopy height. High incidence of no leaf mark (vv) was associated with populations from colder rather than warmer environments. Populations from sites with low rainfall were larger leaved and more upright than populations from wetter sites. Populations from severely grazed sites were less upright and less cyanogenic than populations from infrequently or nil defoliated sites.Deceased     

Evaluating an image analysis system for mapping white clover pastures

We have developed an image analysis system for mapping white clover pastures. The information from digital colour photographs is processed by software (Trifolium.exe) specially designed for the purpose. The software estimates the coverage of clover, weeds and bare ground, and the unidentified remainder of the total area is regarded as covered by grass. To evaluate the reliability of the estimates of clover content, the clover on paper printouts of non-processed images were marked manually and analysed by a photo scanner and commercially available software. The outputs from Trifolium.exe and the estimates from scanned manual markings were highly correlated (r ²=0.81). A sensitivity test was conducted to quantify the impact of changes of six user-adjustable parameters of Trifolium.exe. The software output of clover coverage was sensitive for changes in three, soil coverage for changes in one, and weed coverage for changes in all parameters. The fact that the digital image acquisition and analysis produce nearly continuous and exactly positioned data, implies further that it is a very appropriate tool for analyses of spatial dynamics in grass-clover pastures.     

Suppression of root-knot nematodes in natural and agricultural soils

The potential of the invertebrate communities in agricultural and natural soils to suppress Meloidogyne incognita on coleus (Coleus blumei) was evaluated in two greenhouse experiments. Soil from adjacent natural and agricultural habitats was collected from four locations that had very different soil types (loamy sand, muck, sand and rock). Soil of each type was placed into pots, planted with coleus seedlings, inoculated with 2000 eggs of M. incognita, and arranged in a 4 × 2 factorial design. Root-knot nematodes were suppressed in natural soil compared to agricultural soil for loamy sand, sand and rock soils, but not for muck soil. Plants grew larger and had less root galling in natural soils than in agricultural soils. Free-living nematodes (bacterivores, fungivores, omnivores and predators) were monitored but did not show population patterns consistent with the suppression of root-knot nematodes observed in natural soils. Reasons for the opposite result (higher root-knot levels in natural than in agricultural soil) on muck soil are unknown, but this soil type was very different from the other soils in its unusually high organic matter content and very low levels of omnivorous and predatory nematodes. The agricultural muck in particular was unusually low in fungivorous nematodes and extremely high in levels of sodium and macronutrients. Despite the exception on the muck soil, the relative suppression of root-knot nematodes in natural compared to agricultural soils of the other three soil types (loamy sand, sand and rock) support the idea that potential for nematode suppression may be greater in natural than in agricultural soils.     

Collection and characterization of naturalized populations of white clover (Trifolium repens L.) in Argentina

A collection formed from 53 accessions of white clover stolonswas carried out in naturalized populations from Argentina betweenparallels 26° and 37° South latitudes and 58° to 62°West longitude. Almost half of them (43%) wereobtained from grazed sites. Collected samples were grown in the fieldat Pergamino Experimental Station and compared with a local cultivar.Attributes scored or measured were petiole length, width and lengthof central leaflet, relation width/length, height, growing habit,leaf mark, stolon thickness and density, days to flowering,cyanogenesis, seed yield and winter herbage yield. There weresignificant correlations among seven pairs of characters. Allpopulations were cyanogenic within a range from 40 to 100%.Populations from grazed sites had prostrate habit and lower canopyheight than those from non grazed sites. The collection was clusteredin seven groups. Differences among groups were attributed toagroecological differences in sites of collection. Results obtainedencouraged in Argentina further collection missions for naturalizedpopulations of white clover.     

Genetic diversity of fast-and slow-growing soybean rhizobia determined by random amplified polymorphic DNA analysis

The genetic relationships among six strains of rhizobia, including three strains of Rhizobium fredii and three strains of Bradyrhizobium japonicum, was determined using random amplified polymorphic DNA (RAPD) technique. In this study, 46 arbitrary 10mer primers were employed for RAPD, generating a total of 251 informative fragments. A dendrogram of phylogenetic relationships among the six strains was constructed. The results indicated that geographical distribution may affect phylogeny, as there were closer relationships among the four Taiwanese strains, SB138, SB562, SB368 and SB651, than between these strains and USDA192, which originated from mainland China. The strain USDA110, obtained from the United States, was used in the parsimony analysis. The greatest similarity (55.6%), existed between two strains of B. japonicum, SB562 and SB138, which both, and the lowest R. fredii (44.4%) between two strains of R. fredii, SB368 and USDA192. We also found a RAPD marker specific to the four Taiwanese SB strains used in the study. The RAPD technique is a potential tool for the identification of the genetics and systematics of different populations. Received: 23 January 1997     

Responses to Low P-Supply in Breeding Lines of White Clover (Trifolium Repens L.) Reveals Two Tiers of Responses

Four breeding lines (BLs) of white clover, which range in terms of their disposition to increase biomass in response to low or high phosphate (P) levels in soil, were evaluated further when grown hydroponically. BL 45 increased both fresh and dry weight in response to P-deprivation, while BL 49 displayed the same significant stimulation in response to sufficient P. However, when compared these lines did not accumulate any significantly higher levels of P, and all four lines showed the same changes to root:shoot ratio in response to P-deprivation, as well as the induction of both soluble and cell-wall-associated acid phosphatase activity. These results confirm that there is no direct relationship between growth (as an increase in biomass) and acid phosphatase activity and further some responses to P-deprivation may be common to all genetic backgrounds suggesting that they are not part of the intricate mechanisms governing these responses.     

Genetic diversity of European Miscanthus species revealed by AFLP fingerprinting

The genetic diversity of European species of Miscanthus was analyzed by AFLP technique. The genetic similarity based on six primer combinations yielded about 200 data points. The plant material included 11 clones of M. sinensis, 2 clones of M. sacchariflorus and 31 accessions of M. x giganteus. Furthermore 4 hybrids were created by crossing M. sinensis with M. sacchariflorus clones. Two clusters were found represented by M. sinensis and M. sacchariflorus clones. The M. x giganteus accessions clustered under M. sacchariflorus. A very low genetic diversity was found in the M. x giganteus pool. No polymorphism was detected between micro- and rhizome-propagated M. x giganteus accessions. Many of the M. sacchariflorus clones sampled in Botanical Gardens turned out to be M. x giganteus clones. In the hybridization of M. sinensis and M. sacchariflorus material, self-fertilization of the M. sinensis clones was determined by application of the AFLP technique. In the M. sinensis pool a typical diversification of hybrids was detected according to ornamental selection by horticulture breeders. The AFLP technique is an adequate and powerful tool to evaluate genetic diversification, to analyse the success of hybridizations and to find wrong classifications.     

Effect of selection under cultivation on morphological traits and yield of Ladino white clover landraces

One reason for the relatively low genetic advance realized in forage legumes may be the possible selection, under the severe intraspecific competition occurring naturally during cultivation, of a few high-yielding genotypes that would be of similar value in a broadly-based landrace or old cultivar and a narrowly-based, modern variety. The effect of selection under cultivation was assessed in two Ladino white clover farm landraces. Genotypes collected from each farm after a three-year crop cycle (survivor populations), or obtained from the seed used to establish each meadow (original populations), were multiplied clonally and evaluated in isolation and monoculture conditions for one year. The occurrence of directional selection was observed only in the landrace featured by greater intra-population variation in favour of genotypes with longer petioles (+11%), larger leaf size (+13%), less stolons (–14%) and lower production of heads (–16%). Selection for the first two traits would imply an increase of competitive ability, whilst that for the fourth trait appeared mainly as a correlated response. The trade-off between leaf gigantism and head production could act as a buffering mechanism against rapid change in genotype frequencies following random mating. A slight trend towards directional selection for higher yield (+6%) in the same landrace was not statistically significant. No disruptive or stabilizing selection was observed for any trait in either landrace.     

Residual nitrogen effects on a succeeding oat (Avena sativa L.) Crop of clover species and ryegrass (Lolium perenne L.) undersown in winter wheat (Triticum aestivum L.)

The aim of the present investigation was to study the effect of white clover (var. Milka and Donna), red clover (var. Fanny) and ryegrass (var. Tove) undersown in winter wheat on a succeeding oat crop. Under the climatic conditions prevailing in Sweden, growing a catch crop after winter cereals is of particular interest because the latter are usually followed by a spring sown crop, leaving the ground bare during autumn and winter. Field trials were carried out during three growing seasons in an integrated farming system and for one year in an organic farming system. Competition from the dense wheat crop in the integrated farming system had a negative effect on the undersown species, and at harvest of the wheat they showed quite poor growth in all three years, with nitrogen contents under 5 kg ha^?1. No significant yield increase was measured without added nitrogen when the averages for all three years were calculated. On average, the grain yields were improved by 750 kg ha^?1 (14% moisture content) for the treatments with undersown clover for all three years when 90 kg N ha^?1 were added. The experiment within the organic system showed a different pattern with a better development of the undersown clover species, with nitrogen contents approximately 25 kg ha^?1 and an improvement in oat grain yield, from around 2?000 kg ha^?1 for the control to almost 3?500 kg ha^?1 with clover undersown the previous year.     

Intraspecific variation for tolerance to aluminium toxicity in white clover

A total of 15 populations of white clover (Trifolium repens L.) collected from a variety of soils, and two cultivars of white clover were grown in two solution culture experiments. Concentrations of both aluminium (Al) and phosphorus (P) were varied.

Populations and cultivars of white clover did not differ significantly in response to Al in either experiment, nor was there any evidence that response to Al was correlated with the pH of their native soil. However, genotypes within the various populations and cultivars of white clover differed significantly (p<0.01) in response to Al. Addition of 0.3 mM P alleviated the toxic effects of Al.

Reasons for the apparent lack of population differentiation in response to Al in white clover are discussed.     

Genetic diversity and systematic relationships in sweetpotato (Ipomoea batatas (L.) Lam.) and related species as revealed by RAPD analysis

Summary Fifteen 10mer primers, in combination with the Stoffel fragment, were used to detect random amplified polymorphic DNA (RAPDs) among 26 accessions of sweetpotato (I. batatas (L.) Lam.) from Oceania, Peru, the Philippines, and the United States and between 8 Ipomoea species from section Batatas. Phenetic and principal coordinate analysis of the 56 polymorphisms detected within the hexaploid I. batatas clearly delineated the South Pacific and the Peruvian sweetpotato lines. The two U.S. cultivars clustered with the Oceanic materials. Cladistic and phenetic analysis of 8 Ipomoea species supports previously published phylogenies based on morphological and RFLP data. Among the species examined, I. tabascana, I. trifida and the tetraploid forms of I. batatas from Mexico and Ecuador, including I. batatas var. apiculata, are the taxa most closely related to the cultivated hexaploid I. batatas. These findings support the utility of RAPD markers for evaluating genetic diversity in sweetpotato and for establishing taxonomic and evolutionary relationships in Ipomoea.     

Genetic diversity in Ethiopian barley in relation to altitude

Summary A representative sample of the Ethiopian barley collection, maintained at the Ethiopian Plant Genetic Resources Centre (PGRC/E), was studied for its phenotypic diversity for some agronomic characters, i.e. kernel row number, spike density, spikelets per spike, caryopsis type, kernel colour, thousand grain weight, days to maturity and plant height. The diversity was estimated by using the Shannon-Weaver diversity index (H) for each of the characters to examine overall genetic divergence between accessions on the basis of administrative regions, ecogeographical zones as well as altitudinal ranges within Ethiopia. Most of the variation was due to differences among characters and only a relatively small fraction due to differences between regions. However, almost all characters are considerably influenced by altitude within the regions. The mean diversity index for all characters increases with altitude, reaches a maximum between 2,400 and 2,800 m, and decreases beyond that altitude.     

Enzyme polymorphism and adaptation in strawberry clover (Trifolium fragiferum L.)

Enzymatic survey of eight loci in 22 populations of Trifolium fragiferum L. sampled in three regions in Poland showed regional differences with regard to five genetic parameters describing genetic polymorphism and variability. Differences were attributed to the following climatic variables: annual precipitation, temperature and solar radiation. Continental climatic conditions were favorable for accumulation of genetic polymorphism and variability. Vegetative reproduction versus sexual reproduction had a higher incidence rate under milder climatic conditions. This former mode of reproduction also affected patterns of distribution of variation within regions, by reducing the intra-populational component of total variability.     

花生连作红壤芽孢杆菌的群落多样性及其生防效果研究

芽孢杆菌是土壤中常见的微生物类群,在土壤生态系统中占据重要地位。本研究发现低丘红壤区花生连作红壤中芽孢杆菌的数量为2.0×105 ~ 2.3×105 cfu/g 干土。通过构建3个样品的基因文库,共得到9个种类;16S rDNA 测序结果表明该地区芽孢杆菌的优势类型有短小芽孢杆菌、枯草芽孢杆菌、高地芽孢杆菌,分别占总克隆的54%、12% 和14%。并研究了施用不同微生物制剂对连作花生产量和生育性状的影响,结果显示,施用光合细菌和枯草芽孢杆菌能够在一定程度上提高花生的产量,枯草芽孢杆菌和光合细菌混合施用的增产效果最好,比对照提高了32.14%。     

Genetic diversity among <Emphasis Type="Italic">Jatropha</Emphasis> species as revealed by RAPD markers

The genus Jatropha is native of tropical America with more than 200 species that are widely distributed in tropics with a promise for use as an oil crop for biodiesel. This investigation was carried out to assess the genetic diversity of 12 Jatropha species based on random amplified polymorphic DNA markers. From 26 random primers used, 18 primers gave reproducible amplification banding patterns of 112 polymorphic bands out of 134 bands scored accounting for 80.2% polymorphism across the genotypes. Three primers viz., OPA 4, OPF 11, and OPD 14 generated 100% polymorphic patterns. The polymorphic information content was highest for the primer OPD 14 (0.50) followed by the primers OPF 11 and OPAD 11 (0.48). Jaccard’s coefficient of similarity varied from 0.00 to 0.85, indicative of high level of genetic variation among the genotypes studied. UPGMA cluster analysis indicated three distinct clusters, one comprising all accessions of J. curcas L., while second included six species viz., J. ramanadensis Ramam., J. gossypiifolia L., J. podagrica Hook., J. tanjorensis J. L. Ellis et Saroja J. villosa Wight and J. integerrima Jacq. J. glandulifera Roxb. remained distinct and formed third cluster indicating its higher genetic distinctness from other species. The overall grouping pattern of clustering corresponds well with principal component analysis confirming patterns of genetic diversity observed among the species. The result provides valid guidelines for collection, conservation and characterization of Jatropha genetic resources.     

Invertebrates and nutrients in a Mediterranean vineyard mulched with subterranean clover (Trifolium subterraneum L.)

Summary In the 25-year-old vineyard of a farm near the Maremma National Park (Central Italy), replicate plots were established with a mulch of Trifolium subterraneum L. or cultivation and two levels of fertilizer. The mai objective of this research was to analyse responses by soil invertebrates and nutrients after introducing a herbaceous component into the system; the yield was also considered. The greater availability of organic substrate and the reduced cultivation as a result of green mulching increased the soil mesofauna biomass, especially detritivores. With time, a significant difference became evident between the populations of invertebrates present in the mulched plots and those in the cultivated plots. Over 2 years, most nutrients (Ca, K, P, and N) were significantly increased in the mulched plots compared to the cultivated plots. Grape yields were consistently higher in the bare plots. No significant differences were found in fertilizer effects.     

微卫星标记分析广西水牛遗传多样性

为研究广西沼泽型水牛(Bubalus bubalis)核基因组的多态性,采用23对荧光标记微卫星引物,对随机抽取的60个广西本地水牛样本进行了PCR检测。结果表明,23对引物中,有19对可以获得特异性产物且存在多态,平均有效等位基因数为4.0189,基因座ILSTS086含有13个等位基因;各微卫星基因座的平均杂合度变化范围为0.1852~0.4722,ILSTS019基因座平均杂合度最高(0.4722),而ILSTS017平均杂合度最低(0.1852);群体基因平均多态信息含量(PIC)为0.6639,19个标记中有18个PIC大于0.5,属高度多态位点。