Secondary metabolites from Mycosphaerella ligulicola

(+)-Epoxydon, together with the new (+)-epoxydon monoacetate, 3-methylidene-6-methoxy-1,4-benzodioxan-2-one and 2-(2-hydroxy-5-methoxyphenoxy)-acrylic acid, has been isolated and identified from the mycelium of Mycosphaerella ligulicola grown on Sabouraud-maltose 4 %-agar.     

The survival on chrysanthemum roots of epiphytic mycelium of Mycosphaerella ligulicola

Mycosphaerella ligulicola has been shown to survive as epiphytic mycelium on the root surface of chrysanthemum cuttings: such survival could continue throughout the life of the glasshouse crop. Symptomless surface colonization of roots of cuttings could be induced in non-sterile soil from an inoculum of (a) mycelium and sclerotia or (b) conidia (Ascochyta state); the colonization could spread upwards over the root surface. After 12 weeks survival as an epiphyte on chrysanthemum roots the fungus was still pathogenic to unrooted cuttings. Although the root surfaces of twelve other plants could be colonized by M. ligulicola the fungus survived on these roots for not more than 8 weeks.     

Host range and virulence of five baculoviruses from lepidopterous hosts

The host range and virulence of five insect baculoviruses (two multiply-enveloped nuclear polyhedrosis viruses (MNPVs) from Agrotis segetum and Mamestra brassicae; one singly-enveloped NPV from Plusia gamma and two granulosis viruses (GVs) from A. segetum and Pieris brassicae) were studied for seven lepidopterous pests of temperate agriculture (A. segetum, Agrotis exclamationis, Lacanobia oleracea, M. brassicae, Noctua pronuba, P. gamma and Pieris rapae). None of the viruses killed all species but M. brassicae MNPV failed to infect only P. rapae. The other viruses were restricted to the homologous host, or members of its genus or subfamily. In all examples except A. segetum GV, the median lethal dose for the most susceptible host, was less than 22 virus inclusion bodies and median lethal times for all infections ranged from 5·5 to 16·6 days. The low susceptibility of A. segetum and other noctuids to GV infections is discussed in relation to the structure of inclusion bodies and the nature of the infectious unit in baculoviruses.     

Studies on the influence of leaf washings on infection by Mycosphaerella ligulicola

Infection of chrysanthemum leaf discs by spores of Mycosphaerella ligulicola was increased in the presence of concentrated leaf washings obtained from five plant species tested. On separation of leaf washings by dialysis the residue stimulated infection and caused aggregation of hyphae on leaf and cellophane surfaces. In the presence of the diffusible fraction an extensive branching network of hyphae developed but there was no increase in infection except in the presence of the chrysanthemum diffusate. Infection of leaf discs of certain plants normally resistant to M. ligulicola occurred in the presence of concentrated leaf washings. Leaf washings from a resistant variety of chrysanthemum had the same effects as those from a susceptible variety. An extract of chrysanthemum leaves was less effective in stimulating infection than was a leaf washing. Defined nutrient media and potato extract stimulated infection but caused the development of different growth habits on leaf surfaces. The active components of the dialysis residue of chrysanthemum leaf washings were heat-stable but apparently volatile. Eluates from strips of certain regions of paper chromatographs of leaf washings and potato extract caused increased infection together with development of characteristic growth habits of the fungus on the leaf.     

Comparison of the effect of antibiotic substances on sclerotia of Mycosphaerella ligulicola and Colletotrichum coccodes

Summary Sclerotia ofColletotrichum coccodes tolerated much higher concentrations of actidione in agar than did sclerotia ofMycosphaerella ligulicola. With increase in concentration of the antibiotic sclerotia of both species took longer to germinate. Increased resistance of both species to actidione developed after growth of a single generation on media containing the antibiotic. Sclerotia ofC. coccodes survived 5 days immersion in a bacterial culture filtrate whereas scleroia ofM. ligulicola ceased to be viable after a similar period.Sclerotia ofC. coccodes andM. ligulicola exhibited strand and loose types of formation respectively. The degree of resistance of these sclerotia to antibiotic substances was correlated with both longevity in soil and type of formation, but, in general, there is unlikely to be a relationship between structure of the sclerotium and longevity.     

Host Range of Australian Phoma ligulicola var. inoxydablis Isolates from Pyrethrum

Ray blight, caused by Phoma ligulicola var. inoxydablis is one of the most damaging diseases of pyrethrum ( Tanacetum cinerariifolium [Trevir.] Sch. Bip.) in Australia. The pathogenicity of P. ligulicola var. inoxydablis to a range of ornamental and other plant species was tested to determine potential sources of inoculum into pyrethrum crops. Differences were identified in the host range of P. ligulicola var. inoxydablis isolates in this study in comparison with isolates reported from garden chrysanthemum ( Chrysanthemum morifolium L.), most likely to be P. ligulicola var. ligulicola . Australian P. ligulicola var. inoxydablis isolates were unable to infect and cause disease following repeated inoculation to zinnia ( Zinnia elegans L.), sunflower ( Helianthus annuus L.), dahlia ( Dahlia variabilis Desf.), and several cultivars of crisphead lettuce ( Lactuca sativa L.). French marigold ( Tagetes patula L.) was recorded as a susceptible host for this pathogen for the first time. Moreover, the susceptibility of annual chrysanthemum ( Chrysanthemum carinatum L.) to infection by P. ligulicola var. inoxydablis was confirmed. Implications for disease management in Tasmanian pyrethrum fields are discussed.     

Host range ofFrankia endophytes

Summary Cross-inoculation experiments with 10 pure cultured strains and 17 host species were carried out. The 10 strains were isolated from the root nodules on actinorhizal trees ranging in 9 species, 5 genera and 4 families. The host species belong to 5 genera. The pure cultured strains fromAlnus are of strong ability to infect different species of the same genus. The seedlings inoculated with these strains are able to nodulate normally. These strains can also infect and nodulate the seedlings ofMyrica californica, but not the seedlings of Elaeagnus, Casuarina andMyrica rubra. The pure cultured strains from Elaeagnus can infect and nodulate the host species in the same genus and family with an exception ofE. viridis vardelavayi, which can be only poorly nodulated by a few strains from Elaeagnus. The strains from Elaeagnus cannot infect the seedlings of Alnus andMyrica rubra. The results presented here suggest thatFrankia endophytes can be divided into two groups: Alnus group and Elaeagnus group.     

Host resistance and parasite virulence in greenfinch coccidiosis

The question why different host individuals within a population differ with respect to infection resistance is of fundamental importance for understanding the mechanisms of parasite-mediated selection. We addressed this question by infecting wild-caught captive male greenfinches with intestinal coccidian parasites originating either from single or multiple hosts. Birds with naturally low pre-experimental infection retained their low infection status also after reinfection with multiple strains, indicating that natural infection intensities confer information about the phenotypic ability of individuals to resist novel strains. Exposure to novel strains did not result in protective immunity against the subsequent infection with the same strains. Infection with multiple strains resulted in greater virulence than single-strain infection, indicating that parasites originating from different host individuals are genetically diverse. Our experiment thus demonstrates the validity of important but rarely tested assumptions of many models of parasite-mediated selection in a wild bird species and its common parasite.     

Host density and the evolution of parasite virulence

Social and cultural habits of human populations affect the biological evolution of the agents of infectious diseases. Measles and similar diseases have evolved in the Old World and cannot have existed in their present form before the rise of the great river valley civilizations. It is suggested that increased virulence of measles in white and indigenous communities in America 1500-1800 may be due to a rare strain of the virus, which was selected during transfer from Europe. The release of viruses for biological pest control has provided new material for the study of the co-evolution of host-parasite systems, which has upset the dogma "evolution tends to avirulence". It is pointed out that this issue is closely related to the group selection debate among ethologists, i.e. to the problem: how can group selection overcome individual selection? A model is proposed in which differential growth of two strains of a parasite within the host and their transmission to new hosts is considered. It is supposed that transmission stages excreted by infectious hosts enter a common pool where they are mixed before infecting new hosts. Under these conditions, selection of the slower strain is possible only if the mean size of parasite inoculum is very small, i.e. if the density of transmission stages in the environment is low. The impact of this result on host pathology depends on the relation between virulence and transmission efficiency of the parasite.     

Host specificity and geographic range in haematophagous ectoparasites

A negative interspecific correlation between the degree of habitat specialization and the size of a species' geographic range has been documented for several free living groups of organisms, providing support for the niche breadth hypothesis. In contrast, practically nothing is known about the geographic range sizes of parasitic organisms and their determinants. In the context of the niche breadth hypothesis, parasites represent ideal study systems, because of the well documented variation in host specificity among parasite species. Here, we investigated the relationship between host specificity (a measure of niche breadth) and geographic range size among flea species parasitic on small mammals, using data from seven distinct geographical regions. Two measures of host specificity were used: the number of host species used by a flea species, and a measure of the average taxonomic distance between the host species used by a flea; the latter index provides an evolutionary perspective on host specificity. After correcting for phylogenetic influences, and using either of our two measures of host specificity, the degree of host specificity of fleas was negatively correlated with the size of their geographic range in all seven regions studied here, with only one minor exception. Overall, these results provide strong support for the niche breadth hypothesis, although other explanations cannot be ruled out.     

Host range nodulation and adaptation in frenchbean rhizobia

The host range nodulation efficiency of four genetically marked frenchbean rhizobial strains (HURR-3, Raj-2, Raj-5 and Raj-6) was studied with five legume hosts namely, frenchbean (Phageolus vulgaris L.), pigeonpea [Cajanus cajan (L.) Millsp.], mungbean [Vigna radiata (L.) Wilezek.], urdbean [Vigna mungo (L.) Hepper.] and soybean [Glycine max (L.) Merril.]. Except soybean and pigeonpea, all other legume hosts were nodulated by two or more frenchbean rhizobial strains tested. Rhizobia were isolated from nodules produced by strains, HURR-3 and Raj-5, on main (frenchbean) and different (mungbean and urdbean) hosts. There was marked improvement in host range nodulation and nitrogen fixation efficiency of rhizobial strains, HURR-3 and Raj-5. after their isolation from chance nodules on different hosts. This is clearly evident from the ability of such isolates to form nodules on pigeonpea besides mungbean and urdbean, and higher nodulation in all the above three different hosts. The phage-susceptibility pattern and intrinsic antibiotic resistance (used as markers) of the two strains did not change after their passage through different hosts. The results indicate that frenchbean rhizobia had undergone some modification in symbiotic behaviour to adapt to wide host range during their passage through different (alternate?) hosts.     

悬铃木方翅网蝽寄主范围的测定

在室内选择上海地区的19科27种园林植物对悬铃木方翅网蝽Corythucha ciliata(Say)进行寄主专一性测定。非选择性试验结果表明:悬铃木方翅网蝽对一球悬铃木(Platanus occidentalis)、二球悬铃木(Platanus acerifolia)、三球悬铃木(Platanus orientalis)、红叶李(Prunus cerasifera)、构树(Broussonetia papyrifera)和红花槭(Acer rubrum)6种植物有取食现象,其中若虫在前5种植物上取食量较大,而对红花槭只表现为轻微取食;成虫在前4种植物上的取食量较大,而对构树和红花槭只有少量取食。在所有植物中,悬铃木方翅网蝽只能在一球悬铃木、二球悬铃木、三球悬铃木上完成完整的发育世代。选择性试验表明:成虫嗜食一球悬铃木、二球悬铃木、三球悬铃木,部分取食红叶李,而不取食红花槭和构树。成虫产卵显著偏爱于一球悬铃木、二球悬铃木、三球悬铃木,而不在其它植物上产卵。因此,悬铃木方翅网蝽的寄主范围较为单一,只有悬铃木属植物是其寄主。     

Host plant species affects virulence in monarch butterfly parasites

1. Studies have considered how intrinsic host and parasite properties determine parasite virulence, but have largely ignored the role of extrinsic ecological factors in its expression. 2. We studied how parasite genotype and host plant species interact to determine virulence of the protozoan parasite Ophryocystis elektroscirrha (McLaughlin & Myers 1970) in the monarch butterfly Danaus plexippus L. We infected monarch larvae with one of four parasite genotypes and reared them on two milkweed species that differed in their levels of cardenolides: toxic chemicals involved in predator defence. 3. Parasite infection, replication and virulence were affected strongly by host plant species. While uninfected monarchs lived equally long on both plant species, infected monarchs suffered a greater reduction in their life spans (55% vs. 30%) on the low-cardenolide vs. the high-cardenolide host plant. These life span differences resulted from different levels of parasite replication in monarchs reared on the two plant species. 4. The virulence rank order of parasite genotypes was unaffected by host plant species, suggesting that host plant species affected parasite genotypes similarly, rather than through complex plant species-parasite genotype interactions. 5. Our results demonstrate that host ecology importantly affects parasite virulence, with implications for host-parasite dynamics in natural populations.     

Host range of chlamydiaphages phiCPAR39 and Chp3

The host range of phiCPAR39 is limited to four Chlamydophila species: C. abortus, C. caviae, C. pecorum, and C. pneumoniae. Chp3 (a newly discovered bacteriophage isolated from C. pecorum) shares three of these hosts (C. abortus, C. caviae, and C. pecorum) but can additionally infect Chlamydophila felis. The ability to support replication was directly correlated with the binding properties of the respective bacteriophages with their host species. Binding studies also show that phiCPAR39 and Chp3 use different host receptors to infect the same host cells: cell binding is sensitive to proteinase K treatment, confirming that the chlamydiaphage receptors are proteinaceous in nature.     

Host range and properties of artichoke yellow ringspot virus

The biological, serological and physico-chemical properties of one isolate of artichoke yellow ringspot virus (AYRV) from Greece and another from Italy were compared. Both isolates infected 56 herbaceous species and there were few differences between them in the symptoms they caused. During purification they behaved identically and both tended to aggregate. Virus particles were isometric and measured c. 30 nm in diameter. In CsCl, virus sedimented as mixed aggregates of empty and full particles with buoyant densities varying from 1.20–1.30 g/ml and from 1.40–1.53 g/ml, respectively. The coat protein of AYRV contains a single polypeptide of mol. wt 53000 and the genome consists of two species of single-stranded RNA with mol. wts 2.17 × 10⁶ (RNA-1) and 1.85 × 10⁶ (RNA-2) daltons, estimated under denaturing conditions. The two virus isolates are serologically very closely related but are unrelated to 28 other plant viruses with isometric particles. The characteristics of AYRV suggest that it is a possible member of the nepovirus group.