The Effect of Endophytic Fungi on Nematode Populations in Summer-dormant and Summer-active Tall Fescue

Summer-active (continental) and summer-dormant (Mediterranean) tall fescue morphotypes are each adapted to different environmental conditions. Endophyte presence provides plant parasitic nematode resistance, but not with all endophyte strains and cultivar combinations. This study sought to compare effects of four nematode genera on continental and Mediterranean cultivars infected with common toxic or novel endophyte strains. A 6-mon greenhouse study was conducted with continental cultivars, Kentucky 31 (common toxic) and Texoma MaxQ II (novel endophyte) and the Mediterranean cultivar Flecha MaxQ (novel endophyte). Endophyte-free plants of each cultivar were controls. Each cultivar × endophyte combination was randomly assigned to a control, low or high inoculation rate of a mixed nematode culture containing stunt nematodes (Tylenchorhynchus spp.), ring nematodes (Criconemella spp.), spiral nematodes (Helicotylenchus spp.), and lesion nematodes (Pratylenchus spp.). Endophyte infection had no effect on nematode population densities. The cultivar × endophyte interaction was significant. Population densities of stunt nematode, spiral nematode, and ring nematodes were higher for Flecha MaxQ than other cultivar × endophyte combinations. Novel endophyte infection enhances suitability of Flecha MaxQ as a nematode host.     

燕麦种质资源重要农艺性状适应性和稳定性评价

为客观评价燕麦种质资源重要农艺性状的适应性和稳定性,本研究利用加权隶属函数法分析了81份燕麦种质材料在7个试验点的株高等7个重要农艺性状的遗传差异,以加权隶属函数值(D值)构建基因型×环境的GGE双标图,分析裸燕麦、皮燕麦在不同试验点的适应性和稳定性。结果表明:主穗粒重是裸燕麦材料在所有试验点中变异程度最大的性状,有效分蘖数是皮燕麦中变异程度最大的性状,其余5个性状的变异程度与皮裸性几乎无关;加权隶属函数法结合GGE双标图在对燕麦农艺性状进行综合分析时具有很好的应用价值;坝莜三号、73014-336、二莜麦、Bauntebue、坝燕一号等材料可用于实际生产,其中的坝莜三号、坝燕一号已是当下河北等地区的主栽品种;晋8609-1、LY03-02、二秋莜麦、64燕麦、品16、Banner、LY01-12等可作为杂交育种的亲本材料。     

Identification of a chemically induced point mutation mediating herbicide tolerance in annual medics (Medicago spp.)

Background and Aims: Sulfonylurea (SU) herbicides are used extensively in cereal–livestockfarming zones as effective and cheap herbicides with usefullevels of residual activity. These residues can persist beyondthe cropping year, severely affecting legumes in general, andannual medics in particular, resulting in reduced dry matterproduction, lower seed yields and decreased nitrogen fixation.A strand medic cultivar, Medicago littoralis ‘Angel’,has been developed via chemical mutagenesis with tolerance toSU soil residues. Identifying the molecular basis of the observedtolerance was the aim of this study. Methods: Two F₂ populations were generated from crosses between ‘Angel’and varieties of intolerant M. truncatula, the male-sterilemutant tap and the cultivar ‘Caliph’. Genetic mappingwith SSR (single sequence repeat) and gene-based markers allowedidentification of the trait-defining gene. Quantitative geneexpression studies showed the activity of the respective alleles. Key Results: Segregation ratios indicated the control of SU-herbicide toleranceby a single dominant gene. SU herbicides inhibit the biosynthesisof the branched-chain amino acids by targeting the acetolactatesynthase enzyme, allowing the choice of a mapping approach usingacetolactate synthase (ALS) gene homologues as candidates. SSR-markeranalysis suggested the ALS-gene homologue on chromosome 3 inM. truncatula. The ALS-gene sequences from ‘Angel’and intolerant genotypes were sequenced. In ‘Angel’,a single point mutation from C to T translating into an aminoacid change from proline to leucine was identified. The polymorphismwas used to develop a diagnostic marker for the tolerance trait.Expression of the mutant ALS allele was confirmed by quantitativeRT-PCR and showed no differences at various seedling stagesand treatments to the corresponding wild-type allele. Conclusions: The identification of the trait-defining gene and the developmentof a diagnostic marker enable efficient introgression of thiseconomically important trait in annual medic improvement programs.     

Molecular characterization of larval anisakid nematodes from marine fishes off the Moroccan and Mauritanian coasts

A total of 242 larval forms of Anisakis collected from marine fishes at different sites off the Moroccan and Mauritanian coasts, recognised as belonging to Type I and Type II larvae, were identified by PCR-RFLP (Polymerase Chain Reaction-Restriction Fragment Length Polymorphisms) of the ITS (Internal Transcribed Spacers) region (ITS-1, 5.8 subunit rRNA gene and ITS-2), using a previously established molecular key. The Type I larvae were found with a frequency of 98.34% and were identified as belonging to the following species: A. simplex s.str., A. pegreffii, A. simplex s.str/A. pegreffii heterozygote genotypes, A. typica, A. ziphidarum and Anisakis sp. A. The Type II larvae were found to belong to A. physeteris, with the frequency of 1.65%. The results reported in the present study provide further epizootiological and biological data on the Anisakis spp. in marine fishes off the Moroccan and Mauritanian coasts, improving the picture of the occurrence of these species in the central Atlantic coasts.     

Fine structure of the ventral nerve centre and interspecific identification of individual neurons in the enigmatic Chaetognatha

The enigmatic arrow worms (Chaetognatha) are marine carnivores and among the most abundant planktonic organisms. Their phylogenetic position has been heavily debated for a long time. Most recent molecular studies still provide a diverging picture and suggest arrow worms to be some kind of basal protostomes. In an effort to understand the organization of the nervous system in this clade for a broad comparison with other Metazoa we analysed the ultrastructure of the ventral nerve centre in Spadella cephaloptera by transmission electron microscopy. We were able to identify six different types of neurons in the bilateral somata clusters by means of the cytoplasmic composition (regarding the structure of the neurite and soma including the shape and eu-/heterochromatin ratio within the nucleus) as well as the size and position of these neurons. Furthermore, our study provides new insights into the neuropil composition of the ventral nerve centre and several other fine structural features. Our second goal was to examine if individually identifiable neurons are present in the ventral nerve centres of four chaetognath species, Sagitta setosa, Sagitta enflata, Pterosagitta draco, and Spadella cephaloptera. For that purpose, we processed whole mount specimens of these species for immunolocalization of RFamide-related neuropeptides and analysed them with confocal laser-scanning microscopy. Our experiments provide evidence for the interspecific homology of individual neurons in the ventral nerve centres of these four chaetognath species suggesting that the potential to generate serially arranged neurons with individual identities is part of their ground pattern.     

Differentiation of bermudagrass (Cynodon spp.) genotypes by AFLP analyses

 Bermudagrasses (Cynodon spp.) are major turfgrasses for home lawns, public parks, golf courses and sport fields, and are widely adapted to tropical and warmer temperate climates. Morphological and physiological characteristics are not sufficient to differentiate some bermudagrass genotypes because the differences between them are often subtle and subject to environmental influence. In this study, a DNA-typing technique, amplified fragment length polymorphism (AFLP), was used to differentiate bermudagrass genotypes and to explore their genetic relationships. Twenty seven bermudagrass cultivars and introductions, mostly from the Coastal Plain Experiment Station in Tifton, Ga., were assayed by the radioactive (³²P) and the fluorescence-labeled AFLP methods. The AFLP technique produced enough polymorphism to differentiate all 27 bermudagrass genotypes, even the closely related ones. An average of 48–74 bands in the 30–600-bp size range was detected by the ³²P-labeled AFLP method. The results indicated that most of the 14 primer combinations tested in this study could be used to distinguish bermudagrass genotypes, and that some single primer-pairs could differentiate all 27 of them. To test the reliability and reproducibility of the AFLP procedure, three DNA isolations (replications) of the 27 bermudagrass genotypes were assayed using five primer pairs. Only 0.6% of the bands were evaluated differently among the three replications. One replication of one genotype (which was most likely a planting contaminant) was grouped in an unexpected cluster using the Unweighted Pair Group Mean Average (UPGMA) method. A one- or two-band difference in scoring did not change the clustering of genotypes or the replications within genotypes. The 27 genotypes were grouped into three major clusters, many of which were in agreement with known pedigrees. Trees constructed with different primer combinations using ³²P- and fluorescence-labelling formed similar major groupings. The semi-automated fluorescence-based AFLP technique offered significant improvements on fragment sizing and data handling. It was also more accurate for detection and more efficient than the radioactive labelling method. This study shows that the AFLP technique is a reliable tool for differentiating bermudagrass genotypes and for determining genetic relationships among them. Received: 28 July 1998 / Accepted: 3 November 1998     

Sequence analyses of the ITS regions and the matK gene for determining phylogenetic relationships of Diospyros kaki (persimmon) with other wild Diospyros (Ebenaceae) species

To elucidate the relationships among Diospyros kaki and species closely related in previous studies, the nuclear ribosomal internal transcribed spacer (ITS) DNA sequence and the chloroplast matK gene were sequenced and compared with those of nine Diospyros species from Thailand, four species from temperate regions, and one species of southern Africa, D. lycioides. Maximum parsimony, maximum likelihood, and neighbor joining analyses of the matK and ITS data sets revealed that D. kaki is closely related to two diploid species, D. oleifera and D. glandulosa. D. kaki, D. glandulosa, and D. oleifera were placed differently in the trees obtained from ITS and matK data sets, suggesting that hybridization and/or introgression may have occurred during the development of these species. D. kaki was not found to be closely related to D. ehretioides, a diploid species from Thailand. These results differed from a prior analysis of this genus performed with chloroplast DNA (cpDNA) restriction site mutations in 3.2- and 2.1-kb amplified sequences. The results supported Ng’s hypothesis that D. glandulosa and D. kaki may share a common ancestor. D. oleifera was also closely associated with D. kaki.     

Genetic evidence against a morphologically suggestive conspecificity of Dermacentor reticulatus and D. marginatus (Acari: Ixodidae)

Dermacentor reticulatus and D. marginatus exhibit overlapping phenotypes. The possibility of conspecificity was investigated on the nucleotide level by comparing DNA sequences of the second internal transcribed spacer (ITS 2) of the rDNA gene. The inter-specific polymorphism was more than 20-times greater than the intra-specific polymorphism of 3 D. reticulatus strains of different geographic origins. Furthermore, the degree of polymorphisms between D. reticulatus and D. marginatus was found to be of the same order of magnitude as that between D. andersoni and D. variabilis, for which separate species status is accepted. These genomic findings do not support a possible conspecificity of D. reticulatus and D. marginatus.     

Fungal flora of the digestive tract of 5 species of triatomines vectors of Trypanosoma cruzi,Chagas 1909

A study of the mycobiota in the digestive tract of 5 important species of triatomines, Triatoma brasiliensis, T. infestans, T. sordida, T. pseudomaculata and T. vitticeps, was made. The digestive tracts of 164 adults and 535 nymphs of those triatomines were studied and 393 fungal strains were isolated.The genera with the greatest number of species were Penicillium (19 species), Aspergillus (17 species) and Acremonium (5 species) and the most frequent species, in decreasing order, were Penicillium corylophilum, Aspergillus niger, Penicillium fellutanum, Cladosporium herbarum, Penicillium waksmanii, Aspergillus awamori and Paecilomyces variotii. Among the isolated fungi, we found species that are recognized as entomopathogenic and pathogenic for humans and animals.This revised version was published online in October 2005 with corrections to the Cover Date.     

紫球藻的培养与利用（综述）

紫球藻为单细胞红藻,其细胞富含红藻多糖、多不饱和脂肪酸(主要为AA和EPA）及藻胆蛋白等高价值生物活性物质,在医药和精细化工领域有广泛的应用前景。本文综述紫球藻的生物学特性、生物活性物质、培养与培养特性等方面的研究概况。