Inheritance of antagonistic properties and lytic enzyme activities in sexual crosses of Talaromyces flavus

Two wild-type strains and three benomyl-resistant mutants of the antagonistic ascomycete Talaromyces flavus were crossed in six combinations, two of which yielded hybrid cleistothecia. Parental strains and their ascospore progenies varied in several traits considered to play an important role in the capacity to control soilborne fungal pathogens: extracellular activities of glucose oxidase and cell-wall degrading enzymes, antibiosis towards Verticillium dahliae, and parasitism and biocontrol of Sclerotium rolfsii. A non-Mendelian quantitative mode of inheritance was found for β-1, 3-glucanase and chitinase activities but only the latter exhibited a normal frequency distribution. Some of the progenies exhibited higher glucanase and chitinase activities than those found in the parental strains. Progeny analysis for chitinase, glucanase, cellulase, and glucose oxidase activities revealed no genetic association between any two of these enzymes. Antibiosis was correlated with glucose-oxidase activity in one cross, but not in the other. The ability to reduce bean root rot caused by S. rolfsii was correlated with mycoparasitic activity against S. rolfsii sclerotia in one cross, but not in the other. One out of the 20 progenies tested was able to reduce bean root rot more effectively than its parent strains, thus demonstrating the feasibility of improving a biocontrol agent by conventional breeding.     

Parasitization of the cottony-cushion scale in relation to host size

Measurements of body length of cottony-cushion scales,Icerya purchasi Maskell, are presented. Although length increased markedly with developmental stage, the length distributions of successive stages were found to overlap, making length an imperfect indicator of stage andvice versa. The likelihood of parasitism by the fly,Cryptochaetum iceryae (Williston), was found to increase with increasing scale size when scales of different sizes were concurrently made available to the parasites under field conditions. Also, parasite loads (no. of parasites per parasitized host) were found to increase with host size. The size ofC. iceryae pupae was found to depend on the developmental stage of the scale host in which pupation took place — the more developed (larger) the host, the larger the pupa. This result suggests that parasite growth is food limited in the smaller hosts, and that therefore its apparent preference for larger hosts is to the parasite's advantage.      

A native nitrogen-fixing shrub facilitates weed invasion

Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.     

Biological diversity and cultural heritage

In this paper some examples of the development of communities of microorganisms and plants on historic buildings and montiments are shown. When the building stones differ from the surrounding natural substrata, an increase in the biological diversity of the area is produced. In some cases, monuments can come to constitute a true refuge for a few species when the natural habitat is threatened. It is suggested that biological diversity, when it does not represent a threat for the cultural heritage, should be considered worthy of preservation.     

利用TMV—U1作为载体表达鼠肝炎病毒S糖蛋白片段

为了验证转基因烟草中表达的外壳蛋白（ＣＰ）能够重新包被侵入的烟草花叶病毒（ＴＭＶ）的假设,利用抗原表位标记的方法观察ＣＰ亚单位在病毒５′端的交换。通过ＰＣＲ 方法将来源于鼠肝炎病毒（ＭＨＶ） Ｓ蛋白的两个小肽段（１１ ａ．ａ．和１５ ａ．ａ．）的ＤＮＡ序列分别插入ＴＭＶ－Ｕ１ ＣＰ基因邻近３′端的两个位点,并构建了带有外源序列的ＴＭＶ 侵染克隆Ｖ９ （１１ ａ．ａ．）和Ｅ１５ （１５ ａ．ａ．）。通过体外转录反应,得到Ｖ９ ＲＮＡ 及Ｅ１５ ＲＮＡ。突变病毒ＲＮＡ 侵染烟草（Ｎｉｃｏｔｉａｎａ ｔａｂａｃｕｍ ）后表现不同特性。Ｖ９ 和Ｅ１５ 侵染ＸａｎｔｈｉＮＮ烟草后同野生型ＴＭＶ一样产生枯斑。但是,当它们侵染Ｘａｎｔｈｉｎｎ 烟草时,Ｖ９ 产生同侵染ＸａｎｔｈｉＮＮ 烟草相同的枯斑,而Ｅ１５的特性同ＴＭＶ－Ｕ１几乎完全相同,能对Ｘａｎｔｈｉｎｎ 烟草进行系统侵染并在叶片中聚集大量的带有外源片段的外壳蛋白,而且病毒的结构极其稳定。Ｖ９ 和Ｅ１５ 特性的差异可能是由于外源片段在外壳蛋白中存在位置的不同影响了外壳蛋白的结构所致     

Differential impact of egg predation by Zetzellia mali (Acari: Stigmaeidae) on Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

The differential impact of Zetzellia mali on the phytoseiids Metaseiulus occidentalis and Typhlodromus pyri was studied in the laboratory and by analysis of population from orchard plots that contained either phytoseiid, similar numbers of prey mites and high or low densities of Z. mali. Five hypotheses were evaluated to explain why Z. mali had more impact on M. occidentalis in the field than on T. pyri. Given equal opportunity, Z. mali adult females did not consume more M. occidentalis eggs than T. pyri eggs nor did adult females of either phytoseiid inflict greater mortality on Z. mali eggs or larvae through attack or consumption. There was no difference in the within-tree association of Z. mali adult females with eggs of either phytoseiid species nor were there differences in the way prey mites (all life stages) were spatially partitioned between adult female Z. mali as compared with adults and deutonymphs (combined) of either phytoseiid. The foraging area of adult female Z. mali and the oviposition locations of the two phytoseiids from both field and laboratory data were compared using spatial statistics. Metaseiulus occidentalis laid significantly more eggs in the primary foraging area of adult female Z. mali than T. pyri. This was the only factor identified which may explain the greater impact of Z. mali on M. occidentalis. The impact of these interspecific effects on the persistence of predatory mite guilds and biological control are discussed.     

Pre-inoculation of Ri T-DNA-transformed pea roots with Pseudomonas fluorescens inhibits colonization by Pythium ultimum Trow: an ultrastructural and cytochemical study

The influence exerted by Pseudomonas fluorescens, strain 63-28R, in stimulating plant defense reactions was investigated using an in-vitro system in which Ri T-DNA-transformed pea (Pisum sativum L.) roots were subsequently infected with Pythium ultimum. Cytological investigations of samples from P. fluorescens-inoculated roots revealed that the bacteria multiplied abundantly at the root surface and colonized a small number of epidermal and cortical cells. Penetration of the epidermis occurred through the openings made by the disruption of the fibrillar network at the junction of adjacent epidermal cell walls. Direct cell wall penetration was never observed and bacterial ingress into the root tissues proceeded via an intercellular route. Striking differences in the extent of fungal colonization were observed between bacterized and non-bacterized pea roots following inoculation with P. ultimum. In non-bacterized roots, the pathogen multiplied abundantly through most of the tissues while in bacterized roots, pathogen growth was restricted to the epidermis and the outer cortex. At the root surface, the bacteria interacted with the pathogen, in a way similar to that observed in dual culture tests. Most Pythium cells were severely damaged but fungal penetration by the bacteria was never observed. Droplets of the amorphous material formed upon interaction between the bacteria and the host root were frequently found at the fungal cell surface. Incubation of sections with a -1,4-exoglucanase-gold complex revealed that the cell wall of markedly altered Pythium hyphae was structurally preserved. Successful penetration of the root epidermis was achieved by the few hyphae of P. ultimum that could escape the first defensive line in the rhizosphere. Most hyphae of the pathogen that penetrated the epidermis exhibited considerable changes. The unusual occurrence of polymorphic wall appositions along the host epidermal cells was an indication that the host plant was signalled to defend itself through the elaboration of physical barriers.Abbreviations AGL Aplysia gonad lectin - PGPR plant growth-promoting rhizobacteria The authors wish to thank Sylvain Noël for excellent technical assistance. This study was supported by grants from the Fonds Québécois pour la formation de chercheurs et l'Aide à la Recherche (FCAR), the Natural Sciences and Engineering Council of Canada (NSERC) and the Ministère de l'Industrie, du Commerce, de la Science et de la Technologie (SYNERGIE).     

马桑菌株的生物学特性

对从湖北、四川、云南等地采集的尼泊尔马桑(Coriaria nepalensis Wall.)根瘤中分离的20株内生菌纯培养物所进行的研究表明,其形态均具有弗兰克氏菌属的特征。在粗细不一的分枝菌丝体上有泡囊和孢囊,有的还有串珠状结构的菌丝体。不同菌株在液体培养基上生长速度很不一致;菌丝体多呈絮状或颗粒状沉淀,个别还呈薄膜状沉淀;绝大多数菌株的菌丝体具有不同色调的色素;在S培养基中大多数都能产生可溶性色素。上述这些培养特征常因培养基成分和培养方式的不同而有差异。大多数菌株的胞壁组分属Ⅱ型,少数菌株为Ⅲ型;全细胞糖型变化很大,20个菌株可划分为6个糖型,而且绝大多数糖型与已知弗兰克氏菌有所不同。此外,有65％的菌株还具有明显的抗菌活性。     

Control of Chenopodium album by soil application of Ascochyta caulina under greenhouse conditions

Effects of soil application of Ascochyta caulina spores on seedlings of Chenopodium album and five cultivated plant species were investigated under greenhouse conditions as a part of a study on biological control of C. album. Application of A. caulina spores to soils resulted in disease development on C. album and to a lesser degree on Spinacia oleracea seedlings, but not on Beta vulgaris subspecies vulgaris, Zea mays, Triticum aestivum and Pisum sativum seedlings. Affected C. album seedlings had an abnormal olive-green colour or necrotic spots on cotyledons and hypocotyls, and were stunted or died. Affected S. oleracea seedlings were pale in colour or had necrotic spots on the cotyledons, but did not die. Time courses of disease incidence and of mortality of C. album could be described by a monomolecular model. Effects of spore density, sowing depth, soil water content, soil type and time of sowing on disease development were examined. Disease incidence and mortality were influenced by spore density, soil water content and soil type, but not by sowing depth. Spores in a moist soil maintained infectivity at least 2 wk. Spore densities of 10⁹ to 10¹⁰ spores m^-2 were required for 50% mortality of emerged C. album plants. Aspects of the development of A. caulina into a soil-applied mycoherbicide are discussed.     

Resource-mediated effects of stream pollution on food absorption of Asellus aquaticus (L.) populations

The role of interactions between chemical perturbations and biological constraints on detritivores occurring in polluted streams were investigated by analysing food absorption variation with stress. Absorption rate and efficiency of four Asellus aquaticus (L.) populations from differently polluted habitats were quantified with respect to the microbial guilds colonizing detritus. A twin tracer method was used. Detritus was microbially colonized in standard conditions and on each stream bottom to control for potential resource-independent variations among individuals. The relationship between length and weight was also determined on a random sample of individuals of each population. Differences of 14.6% in potential absorption efficiency and 11.3% in potential absorption rate were observed between populations from the least and the most polluted habitat. Actual (realized) variations were much stronger: from a minimum of a 60.1% reduction in absorption efficiency to a maximum of 93.8% for the rate. The realized food absorption and the individual weight per length showed the same pattern of variation among populations. This suggested that the availability of energy to isopods in nature was related to stream pollution and resource quality. Bottomup interactions appear to be the most relevant pathway through which chemical water pollution affects the Asellus populations studied. The potential resource-independent variations among individuals are also likely to be explained by temporal cascading of resource-mediated effects.