Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.     

卷曲乳杆菌对三种结肠上皮细胞的粘附性

目的 研究卷曲乳杆菌对3种结肠上皮细胞（SW480细胞、SW620细胞、LOVO细胞）的粘附性。方法 将处于对数生长期的卷曲乳杆菌A7分别与SW480细胞、SW620细胞、LOVO细胞进行体外粘附试验,革兰染色后显微镜观察卷曲乳杆菌A7对3种结肠上皮细胞的粘附结果并计数。结果 卷曲乳杆菌A7对3种结肠上皮细胞的粘附均具有显著性,其中对于SW480细胞和LOVO细胞的粘附性明显高于SW620细胞。结论 卷曲乳杆菌A7对SW480细胞、SW620细胞、LOVO细胞均具有较强的粘附性,提示该菌株有望成为肠道益生菌的新成员。     

The Bacterial Peptide Pheromone Plantaricin A Permeabilizes Cancerous, but not Normal, Rat Pituitary Cells and Differentiates between the Outer and Inner Membrane Leaflet

Plantaricin A (PlnA) is a 26-mer peptide pheromone with membrane-permeabilizing, strain-specific antibacterial activity, produced by Lactobacillus plantarum C11. We investigated the membrane-permeabilizing effects of PlnA on cultured cancerous and normal rat anterior pituitary cells using patch-clamp techniques and microfluorometry (fura-2). Cancerous cells displayed massive permeabilization within 5 s after exposure to 10–100 μm PlnA. The membrane depolarized to nearly 0 mV, and the membrane resistance decreased to a mere fraction of the initial value after less than 1 min. In outside-out membrane patches, 10 μm PlnA induced membrane currents reversing at 0 mV, which is compatible with an unspecific conductance increase. The d and l forms of the peptide had similar potency, indicating a nonchiral mechanism for the membrane-permeabilizing effect. Surprisingly, inside-out patches were insensitive to 1 mm PlnA. Primary cultures of normal rat anterior pituitary cells were also insensitive to the peptide. Thus, PlnA differentiates between plasma membranes and membrane leaflets. Microfluorometric recordings of [Ca²⁺] _i and cytosolic concentration of fluorochrome verified the rapid permeabilizing effect of PlnA on cancerous cells and the insensitivity of normal pituitary cells.     

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     

环丙沙星预先处理牙鲆消化道对干酪乳杆菌定植的影响

利用1株干酪乳杆菌,通过实验研究用环丙沙星预先处理牙鲆消化道后乳杆菌的定植和演替规律。在投喂含有1.2×10^9CFU/g乳杆菌的饲料5 d后,消化道定植的乳杆菌超过106CFU/g,其后维持在10^6～10^8CFU/g动态平衡中。同时随着乳杆菌的投喂,不经环丙沙星预先处理牙鲆消化道的正常组,鱼消化道的弧菌数从10^7～8CFU/g降低到10^6CFU/g左右;而经环丙沙星预先处理牙鲆消化道的药饵组,鱼胃、小肠和盲囊的弧菌数则是先增加,然后显著下降。停喂乳杆菌7 d后,2个实验组鱼消化道的乳杆菌均从10^5～6CFU/g下降到10^4CFU/g,干酪乳杆菌正常组鱼盲囊中弧菌从10^5CFU/g回升到10^6CFU/g,胃和小肠中弧菌数量基本不变。干酪乳杆菌药饵组则有所不同：除胃中弧菌数量则基本不变外,盲囊和小肠中弧菌数量继续下降,其原因有待进一步研究。实验结果表明,干酪乳杆菌能在牙鲆消化道内定植,而用预先处理牙鲆消化道后,更有利于乳杆菌的定植;乳杆菌的投喂和定植,使牙鲆消化道中的弧菌数量明显下降。     

Local and regional assessments of the impacts of plant invaders on vegetation structure and soil properties of Mediterranean islands

Aims Although biological invasions occur throughout the world, and some invaders are widespread in many habitats, few studies on the ecological impact of invaders have examined multiple sites. We tested how the impact of three widespread plant invaders changed depending on the identity of the species and the invaded island. We also tested whether relative species loss was lower in species‐rich communities than in species‐poor ones. Location We conducted floristic surveys and soil analyses in eight Mediterranean Basin islands: Crete and Lesbos (Greece), Sardinia (Italy), Corsica, Bagaud and Porquerolles (France), and Mallorca and Menorca (Spain). Methods We compared native species richness and diversity, proportion of life forms, soil percentage nitrogen, percentage organic carbon, C/N, and soil pH in nearby paired plots of 2 × 2 m: one control and one invaded by either the deciduous tree Ailanthus altissima, the succulent subshrubs Carpobrotus spp. or the annual geophyte Oxalis pes‐caprae, across eight Mediterranean Basin islands. Results On average, the presence of invaders reduced species diversity, Carpobrotus spp. exhibiting the largest impact and Oxalis the least. However, the relative impact was island‐dependent, and was positively but weakly associated with the species richness of the recipient community. Therophytes were the life form that experienced the largest decrease across islands. The effects of invasion on soil properties were very variable. Total N changed (increased) only in plots invaded by Ailanthus, significantly decreasing the C/N ratio. The presence of this tree increased soil pH, whereas the opposite was found in plots invaded by the other two species. Organic C increased in plots invaded by Ailanthus and Carpobrotus species. Main conclusions By conducting an analysis at multiple sites, we found that the three plant invaders had an impact on plant community structure not entirely concordant with changes in soil properties. The impacts depended on the identity of the species and of the invaded island, suggesting that impact of invaders is context‐specific. The impact in terms of species loss was not lower in species‐rich than in species‐poor communities.     

Breeding soybeans for the tropics capable of nodulating effectively with indigenousRhizobium spp.

Summary Most soybean varieties fail to nodulate effectively in tropical soils unless inoculated with a competitive strain ofRhizobium japonicum. Developing countries in the tropics, with few exceptions, lack inoculant industries to produce and distribute viable inoculants to small farmers and extension programs to teach them to use inoculant. Several soybean genotypes have been identified that nodulate effectively with many strains of the cowpea inoculation group which is ubiquitous in tropical soils of Africa. Soybean genotypes that nodulate and grow well without inoculant application are called promiscuous. Methodologies for incorporation of the promiscuity character into high-yielding backgrounds are discussed.Supported in part by grant 05-0560 from United Nations Development Program to the International Institute of Tropical Agriculture.     

Adsorption of temperate phages of Lactobacillus delbrueckii strains and phage resistance linked to their cell diversity

Aims: The aim of this work was to study the adsorption step of two new temperate bacteriophages (Cb1/204 and Cb1/342) of Lactobacillus delbrueckii and to isolate phage‐resistant derivatives with interesting technological properties. Methods and Results: The effect of divalent cations, pH, temperature and cell viability on adsorption step was analysed. The Ca²⁺ presence was necessary for the phage Cb1/342 but not for the phage Cb1/204. Both phages showed to be stable at pH values between 3 and 8. Their adsorption rates decreased considerably at pH 8 but remained high at acid pH values. The optimum temperatures for the adsorption step were between 30 and 40°C. For the phage Cb1/342, nonviable cells adsorbed a lower quantity of phage particles in comparison with the viable ones, a fact that could be linked to disorganization of phage receptor sites and/or to the physiological cellular state. The isolation of phage‐resistant derivatives with good technological properties from the sensitive strains and their relationship with the cell heterogeneity of the strains were also made. Conclusions: Characterization of the adsorption step for the first temperate Lact. delbrueckii phages isolated in Argentina was made, and phage‐resistant derivatives of their host strains were obtained. Significance and Impact of the Study: Some phage‐resistant derivatives isolated exhibited good technological properties with the prospective to be used at industrial level.     

Cold activity of Beauveria and Metarhizium, and thermotolerance of Beauveria

Heat and cold are environmental abiotic factors that restrict the use of entomopathogenic fungi as agents for biological control of insects. The thermotolerance and cold activity of 60 entomopathogenic fungal isolates, including five species of Beauveria and one isolate of Engyodontium albus (=Beauveria alba) were examined as to tolerance of temperatures that might be encountered during field use. In addition, cold activity of eight Metarhizium spp. isolates was evaluated. The isolates were from various geographic regions, arthropod hosts or substrates. High variability in conidial thermotolerance was found among the Beauveria spp. isolates after exposure to 45 °C for 2 h, as evidenced by low (0-20%), medium (20-60%), or high germination (60-80%). The thermal death point (0% germination) for three rather thermotolerant B. bassiana isolates (CG 138, GHA and ARSEF 252) was 46 °C for 6 h. At low temperatures (5 °C), with few exceptions (e.g. CG 66, UFPE 479, CG 227, CG 02), most of the B. bassiana isolates germinated well (ca. 100%). On the other hand, only one isolate of Metarhizium sp. was cold-active (i.e. ARSEF 4343 from Macquarie Island, 54.4°S, Australia). This probably is a M. frigidum isolate. The E. albus isolate (UFPE 3138) was the most susceptible isolate to both heat and cold stress. Isolates ARSEF 252 and GHA of B. bassiana, on the other hand, presented exceptionally high thermotolerance and cold activity. Some isolates with high cold activity, however, were thermosensitive (e.g. ARSEF 1682) and others with high thermotolerance had low cold activity (e.g. CG 227). An attempt to correlate the latitude of origin with thermotolerance or cold activity indicated that B. bassiana isolates from higher latitudes were more cold-active than isolates from nearer the equator, but there was not a similar correlation for heat.     

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.