Secondary Conidia Research Articles

Spore germination in the entomopathogenic genus Aschersonia

In vitro studies of collections of Aschersonia from forest insects (Homoptera) in Brazil and Madagascar have revealed an unusual type of spore germination. Conidia germinate with one to several, long, slender, hair-like, conidiogenous cells producing solitary, mucus-covered secondary conidia apically. These Hirsutella -like structures are described and illustrated and compared with the capillary sporophores (capillisporophores) and capillispores characteristic of some genera of Entomophthorales. They are considered to represent a specific adaptation to an entomopathogenic habit.

Investigations of Entomophthora muscae (Cohn) (Entomophthorales: Entomophthoraceae) conidial infection on housefly Musca domestica (Linn.) by scanning electron microscopy

An entomogenous fungus, Entomophthora muscae, was studied morphologically with respect to the formation of primary and secondary conidia and germ tubes. The fungus penetrated the insect cuticle by germ tubes that were produced at the base of each conidium that penetrated directly through the cuticle. Fungal germ-tube formation and penetration of host integument were observed. The tough germ-tube penetration point seemed to provide abundant energy for the penetration of the host integument. Conidia not directly on the integument formed secondary conidia but were never observed to form germ tubes. Neither appressorium nor infection cushion was observed on the germ tubes.Key words: Entomophthora muscae, entomogenous fungus, insect mycosis, insect pathology, conidia.

A histological study of the invasive and developmental processes of the aphid pathogen Erynia neoaphidis (Zygomycotina: Entomophthorales) in the pea aphid Acyrthosiphon pisum

On landing on the surface of an aphid host, the primary conidium of Erynia neoaphidis produced either a secondary conidium, a germ tube, or an appressorium. Appressoria were usually globose or clavate and each produced a single penetration peg. A circular bore hole marked the penetration site. Once the fungus had breached the cuticle, it formed protoplasts that failed to elicit an obvious immune response and multiplied rapidly in the haemocoel and in tissues. When the body of the host was occluded (about 3 days after penetration at 20 °C), the protoplasts regenerated a wall and differentiated into rhizoids, which were confined to the midventral region of the dead insect, pseudocystidia, and conidiophores. The rhizoids terminated in a digitate holdfast that adhered firmly to the plant cuticle but did not penetrate it. Conidiophores appeared to break out through the host cuticle using a combination of enzymatic and mechanical means. Key words: Erynia neoaphidis, Entomophthorales, infection, development, aphid.

Ultrastructure of conidial germ-tube development in vitro by the insect pathogen Entomophaga aulicae

In an effort to understand the factors influencing the formation of infection structures by the insect pathogen Entomophaga aulicae, we examined the ultrastructural development of conidial germ tubes formed in vitro under conditions that resemble those producing appressoria and protoplasts during infection. Conidia germinated on formvar in a nonaqueous environment produced a single viable germ tube, which in turn produced appressorium-like structures or secondary conidia, structures similar to those formed on the host. The formation of appressorium-like structures indicates that stimuli for appressorium formation are relatively nonspecific, whereas development of the infection hypha requires different triggers. Conidia germinated in a liquid culture medium, which supports the growth of the protoplast stage of the fungus, produced a single viable germ tube that continued to grow apically. This apical growth was accompanied by the loss of the outer layer of the germ tube wall and the presence of electron-opaque granules in an extensive system of cytoplasmic membranes. Protoplasts did not form directly from these germ tubes and ultrastructural details of tip growth in this medium did not resemble those previously described in infection hyphae prior to protoplast formation in the host.

Leaf blight of day lily caused by Aureobasidium microstictum (Bubak) W.B. Cooke.

Brown spots and yellow stripes were observed on leaves of Hemerocallis fulva var. kwanso at the herbal garden of Kyoto Prefectural Research Institute of Agriculture in Ayabe in the late June of 1985. In the beginning, small brown spots appeared on both sides of the leaves and then bright yellow stripes occurred and brownings expanded gradually from the leaf tips. These symptoms had been observed until mid-November. No pathogen was generally observed on diseased leaves, while acervuli composed of the tightly interwoven hyphae were formed on host plants in moist chamber. Conidiogenous cells were clavate to subcylindrical. Conidia were blastic, ellipsoidal to fusoid, hyaline, smooth, one-celled. Inoculation tests indicated that isolates were pathogenic on injured leaves of H. fulva var. kwanso, H. fulva var. disticha, and H. fulva var. fulva. An isolate from naturally infected H. fulva var. disticha showed the same pathogenicity as those from H. fulva var. kwanso. On PDA medium, single conidium isolates formed creamy and yeastlike colonies at first, then after formed white hyphae, and eventually turned dark brown to black in color. Growth on PSA medium occurred in the range from 8 to 30C and optimum growth at between 20 and 24C. Conidia formed on PDA medium were blastic, ellipsoidal to fusoid, hyaline, smooth, one-celled. Secondary conidia were formed and yeastlike growth appeared. On the basis of its morphological characteristics and pathogenicity on the plants of the genus Hemerocallis, the present fungus was identified as Aureobasidium microstictum (Bubak) W.B. Cooke, and a common name, leaf blight, was proposed.

An isolate of Entomophthora pseudococci with two kinds of secondary conidia

The production of two types of secondary conidia, globose and ellipsoidal, is described in an isolate of Entomophthora pseudococci .

Integumental penetration of the pea aphid, Acyrthosiphon pisum, by Conidiobolus obscurus (Entomophthoracease)

Conidiospores of Conidiobolus obscurus adhered to and germinated on the surface of the pea aphid cuticle. Conidial germination was manifested by the formation of either a secondary conidium or one or more germ tubes. The germ tubes manifested two types of behavior: direct penetration or errant growth. Penetration was restricted to the thorax and abdomen, with a low number of penetrating hyphae (< 10% of germinating conidia). Penetrating hyphae gave no evidence of appressoria. Perforation of the cuticle was achieved by mechanical and apparent enzymatic means.

Entomophthora brevinucleata sp. nov. [Zygomycetes, Entomophthoraceae], a pathogen of gall midges [Dip.: Cecidomyiidae

Entomophthora brevinucleata, a fungal pathogen of gall midges, is described. The species occurs on at least 3 host species, including the wheat blossom midgeSitodiplosis mosellana Gehin andMycodiplosis sp.E. brevinucleata produces rhizoids, either monohyphal or comprising bundles of a few hyphae, without holdfasts. The hyphal bodies are subspherical with mean dimensions of 27.5×22.1 μm. The primary conidia are campanulate with mean dimensions from individual hosts of 11.2–18.9×8.7–15.8 μm. They contain 3–13 nuclei with a mean diameter of between 2.7 and 3.7 μm stained with lactophenol-aceto-orcein. The secondary conidia are of similar shape but smaller. Cystidia and resting spores were not observed.

Blastobotrys, Sporothrix and Trichosporiella: generic delimitation, new species, and a Stephanoascus teleomorph.

The morphological and physiological characters of the species of Blastobotrys, and of a number of similar species of Sporothrix, Trichosporiella and Candida were studied. Blastobotrys is defined as having mother cells (primary conidia) which form distinct, secondary conidia. Sporothrix has non-catenulate conidia, or the conidia are catenulate without marked differentiation of conidia of first and second order. Trichosporiella is delimited from Candida by a stronger coherence between hyphal cells, arthroconidia being absent. Four new Blastobotrys species are described, and two unnamed species; two new combinations are proposed in Trichosporiella. Related species in other genera are briefly discussed. A new Stephanoascus teleomorph is described in two strains originally identified as Sp. fungorum. Two diagnostic keys to the described taxa, using either morphological or physiological characters, are given.

A mycosis of the black fly Simulium decorum (Simuliidae) caused by Erynia curvispora (Entomophthoraceae)

Adult black flies (Simulium decorum) that succumbed to infections caused by Erynia curvispora(= Entomophthora curvispora) were found in Ithaca, New York. Other than hyphal elements of the fungus, the only recognizable structures found within most cadavers were remnants of the tracheal system. Several female cadavers contained well developed eggs. A few males contained shrivelled testes. Germination of primary conidia produced: 1, secondary conidia similar to the primaries or; 2, rounded secondary conidia or; 3, very long germ tubes. In vitro culture of E. curvispora was achieved but its ability to sporulate and to grow vegetatively gradually disappeared. Insectary-reared S. vittatum and S. pictipes were experimentally infected by conidia from in vitro cultures in the laboratory. The incubation period of the disease under these conditions was about six days. In nature the mycosis not only decreases the life expectancy of black flies but probably limits their egg-producing capabilities as well. The mycosis probably compromises the fly's ability to vector filarial worms that cause diseases of man and other mammals.

Zoophthora radicans andZoophthora petchi sp. nov. [Zygomycetes: Entomophthorales], two species of the “Sphaerosperma group” attacking leaf-hoppers and frog-hoppers [Hom.

Most isolates of “sphaerosperma group” fungi described by different authors from leaf-hoppers and frog-hoppers appear to fit intoEntomophthora sphaerossperma (Fresenius)sensu strictoRemaudiereet al. (1976) synonymous withZoophthora radicans (Brefeld)Batko. One of these fungi had been described byRostrup in 1896 as a new species,Entomophthora aphrophorae, but although resemblingZoophthora radicans, it cannot be reliably identified because of its incomplete description.Petch, in 1935, erred in giving under that name a detailed description of a fungus from the same host species, as the 2 were morphologically different.Petch's fungus differs from bothEntomophthora aphrophorae andZoophthora radicans by having longer and wider (by ca. 25%) primary and secondary conidia. It differs from the other species of the “sphaerosperma group” in the shape and/or dimensions and length/width ratio of the different kinds of conidia and capillispores. Accordingly, a new name is proposed for this taxon:Zoophthora petchiBen-Ze'ev & Kenneth, sp. nov.

POSITIVE PHOTOTROPISM AND HYDROMORPHOGENESIS IN GERMINATION STRUCTURES OF CONIDIOBOLUS SPECIES

ABSTRACT The mode of germination of conidia of the tested fungi was dependent upon water. The short, wide conidiophores which formed on conidia normally produced secondary conidia spontaneously; however, if they contacted moisture before initiation of secondary conidia could occur, they turned into germ-tubes instead. Since these conidiophores are known to sprout towards light, illumination through agar media, for instance, led to their contacting the wet substrate, resulting in germ-tube formation. Germ-tubes followed the direction of eight narrow wave-bands of light from near ultra-violet through red, by tip-displacement mechanism, and they could be considered homologous to conidial conidiophores. Hyphae of C. obscurus on water agar grew towards light. In darkness, media composition determined direction of sprouting from conidia, and hence their mode of germination.

Behavior of Alternaria brassicae and its mycoparasite Nectria inventa on intact and on excised leaves of rapeseed

On intact leaves of two cultivars (cv.) of rapeseed, Midas (Brassica napus) and Torch (B. campestris), conidia of Alternaria brassicae germinated at a rate of 12.1% and 19.5%, respectively, at 9 h after inoculation. They germinated usually by producing either germ tubes or secondary conidia. Penetration of leaves by A. brassicae was abundant at 24 h and occurred either with or without the formation of appressoria. Penetration of cv. Torch leaves by the fungus occurred either directly through epidermal cells or indirectly through stomata, while cv. Midas leaves were penetrated almost exclusively through stomata. Blackspot lesions developed within 48 h after inoculation.Conidia of Nectria inventa required at least 24 h to initiate germination and 4 days to parasitize A. brassicae on intact leaves. Therefore, N. inventa did not prevent primary infection of the leaves by A. brassicae. Instead, N. inventa suppressed the vegetative growth and sporulation of A. brassicae on excised rapeseed leaves.

Production of Secondary Conidia by Helicoma Proliferans

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Production of Secondary Conidia by Helicoma proliferans

Production of Secondary Conidia by Helicoma proliferans

The fine structure of conidium development in Phialocephala dimorphospora

Sequential developmental stages from synchronously sporulating cultures of Phialocephala dimorphospora Kendrick have been examined. Apical vesicles characterize growth of the primary conidium. These are not, however, seen during secondary conidium formation; instead, large vesicles containing minute membrane fragments develop just below the phialide neck and contribute to wall formation as they fuse with the plasmalemma. The occurrence of microtubules in the neck of the phialide is restricted to primary conidium formation. Just as the primary conidial initial begins to swell, electron-dense granules 50-75 nm in diameter arise in association with the plasmalemma. Such granules are not seen during secondary conidium formation; they are thought to be involved in pigment deposition in the collarette. During both primary and secondary conidium production the conidia go through a sequence of maturation in which the cytoplasm becomes very dense and contains lipid bodies and flocculent aggregations of electron-transparent granules. Subsequently the conidia become less electron dense and reveal a simple internal substructure consisting of a nucleus, mitochondria, micro-bodies, free ribosomes, and presumed storage bodies. The plasmalemma becomes convoluted in a network of interdigitated grooves. Septum formation occurs rapidly and involves the fusion of vesicles with the lateral wall. Mature septa are non-perforate. Although Woronin bodies have been repeatedly observed in young conidia, they are never seen in mature conidia. Myelin figures associated with mitochondria occur consistently in the body of the phialide during conidiation. These may be the source of the lipid bodies in the conidia. In phialides from cultures over 1 week old, signs of senescence are apparent. These include vacuolization of the upper portion of the phialide and the presence of many disorganized sheets of membrane. Spores still present within the collarette of such phialides are smaller than those produced early in the life of the phialide.

Effect of pH and light on conidium germination in Basidiobolus ranarum

Conidia of Basidiobolus ranarum Eidam were incubated on agars which incorporated zwitterionic buffers. On water agar germination was almost entirely by formation of globose secondary conidia. In light, after 4 h, a particularly high germination level (> 97%) occurred at pH 7·0–9·0. In dark, only at pH 8·0–8·5 was this approached (50–70%). On malt agar both in light and dark vegetative germination (> 98%) predominated at pH 5·0–7·0 but was largely replaced by secondary spore formation at about pH 9·0. The two modes of germination have different though overlapping pH ranges. Conidium development by production of elongate secondary spores was rarely encountered and no endospore formation was observed.

Sporulation mutants in Cochliobolus carbonum

Three types of mutants were induced in cultures of Cochliobolus carbonum by ultraviolet irradiation. The mutant C1 abc formed abnormally shaped conidia which proliferated in chains rather than being arranged in a spiral on the conidiophore as in wild-type isolates; a second mutant, C2 pcg, produced conidia which germinated precociously while still attached to the conidiophore and which formed secondary conidia at the ends of short germ tubes; and the third, C1 nc1, formed no conidia. A fourth mutant, C1 nc2, which also failed to form conidia was isolated from a culture grown on a medium containing acriflavin. A 1: 1 segregation ratio was obtained in crosses of C1 abc × wild type, but in crossesC2 pcg × wild type and C1 nc1 × wild type nearly all of the progeny were wild type. The mutants C2 pcg and C1 nc1 failed to form perithecia but could serve as male parents; C1 nc2 was completely infertile. Preliminary attempts to determine whether the pcg and nc mutants were controlled cytoplasmically were inconclusive.

Nematophagous fungi: Meristacrum

Conidia of Meristacrum asterospermum were found to be forcibly ejected, supporting the position of this fungus in the Entomophthoraceae. Conidia adhering to the integument of a live nematode either penetrate directly by a germ tube or germinate externally and produce secondary conidia. Resting spores germinate and produce a single erect conidiophore similar to those produced by thallodic segments.

The nature of the secondary conidia of Sporothrix schenckii.

Observations of secondary conidium production in an African strain ofS. schenckii revealed that secondary conidia are produced (1) acropetally on short sterigmata, (2) sympodially on short conidial appendages, and/or (3) sympodially or acropetally on short sporogenous cells which arise directly from the primary conidium. The secondary conidia therefore appear also to be sympodulospores.