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Plant-parasitic nematodes like root-knot and cyst nematodes are global pests of agricultural and horticultural crops, causing severe yield losses. The penetration of plant roots by juveniles of root-knot nematodes particularly Meloidogyne incognita leads to a surge in physiological and physical changes which results in the formation of giant cells and galls in the root. Nematophagous fungi are widespread in soil. Nematophagous fungi are natural antagonists of nematodes and are considered potential biological control agents of nematodes. They are environmentally beneficial and inexpensive alternatives to nematicides. They have the capacity to capture prey or parasitize and kill nematodes at all stages of their life cycle like eggs, juvenile females and cysts. They fall in four categories: (1) nematode-trapping or predatory fungi which kill the nematodes by producing either adhesive or non-adhesive trapping devices. They possess comparatively good saprophytic ability. Adhesive devices such as hyphae, branches, knobs and nets are coated with adhesive which firmly hold the nematode leading to penetration and colonization by the fungi. Non-adhesive trapping devices are constricting and non-constricting rings. (2) Endoparasitic fungi use adhesive or palatable conidia to enter the nematode body. They are obligate parasites, grow at the expense of body content and finally kill the nematode. Members of Chytridiomycota and Oomycota produce uni- and biflagellate zoospores respectively, to parasitize the nematodes. (3) Parasites of cyst and root-knot nematodes utilize females or eggs as food source, colonizing by the growth of somatic hyphae and causing enzymatic dissolution of egg shell and larval cuticle. These fungi are involved in the degradation of cysts in soil over time. They clearly have the capacity to regulate its host population in soil. (4) Toxin-producing fungi immobilize nematodes by secreting toxins. Most studied potential biological control agents of nematodes are Arthrobotrys oligospora, Pochonia chlamydosporia (syn. Verticillium chlamydosporium), Purpureocillium lilacinum (syn. Paecilomyces lilacinus) and Oomycete Nematophthora gynophila.

Mating crosses in all possible combinations between 15 monoascosporic isolates ofDidymella rabiei (Ascomycotina, Dothideales), derived from diseased chickpea stems collected at a single location in Genesee, Idaho, were prepared on sterile chickpea stem pieces incubated on moist sterile filter papers in glass petri dishes for 5-6 weeks at 10 C or in nylon mesh bags placed on the soil surface outdoors to overwinter for 6 months. The discharge of large numbers of viable ascospores from mature pseudothecia forming on the chickpea stems was indication of successful matings. Pairings between sympatric isolates demonstrated that the fungus is heterothallic with a unifactorial (bipolar) homogenic mating incompatibility system. Papazian test pairings between tester strains and mating types from three locations in Idaho and Washington indi? cated the absence of complete interfertility between allopatric populations and provided strong evidence that the fungus is biallelic, lacking multiple alleles at the single mating locus. The nuclear content of so? matic and reproductive cells at all phases of the life cycle was examined using Giemsa stain. Ascospores and conidia were commonly multinucleate and ap? peared to undergo multiple mitotic divisions prior to germination. Somatic hyphae derived from ascospores and conidia were predominately uninucleate. The importance of sexual reproduction, sexual incompati? bility, and the teleomorph in the disease cycle is dis? cussed relative to environmental factors required for their occurrence and implications for disease control.

We investigated nuclear behavior during basidiosporogenesis in Lentinw, Panus, and Neolenti- nus in an attempt to discover characters for taxonomic segregation of lentinoid-pleurotoid fungi. In Lentinus tigrinus and Panus lecomtei somatic hyphae are binu- cleate. Karyogamy and meiosis occur in the basidia, meiotic products migrate into spores and postmeiotic mitosis occurs; this is followed by back-migration of one nucleus from each spore into the basidium. Ma- ture spores are consequently uninucleate and dis- charged basidia are quadrinucleate. In Neolentinus le- pideus many somatic cells are multinucleate. Karyogamy, meiosis, and postmeiotic mitosis occur as in L. tigrinus and P. lecomtei, but there is no back- migration, mature spores are binucleate, and dis- charged basidia are anucleate. The patterns of nuclear behavior in L. tigrinus and P. lecomtei correspond to type C nuclear behavior as defined by Duncan and Galbraith, whereas that of Neolentinus corresponds to type D nuclear behavior. Lentinus and Panus cannot be distinguished on the basis of postmeiotic nuclear behavior, but both can be distinguished from Pleurotus

An electron microscopic study of clamp formation and conjugate nuclear division was made of the somatic hyphae of Pleurotus ostreatus. Cytoplasmic organization of the growing clamp apex resembles t...

We led mycological field courses in Algonquin Park, Ontario, during September of 1991 and 1992. On each occasion, though in different parts of the park, while making collections of other microfungi on dead leaves, we inadvertently made a small collection of a delicate, colorless, undescribed organism. While this obviously belonged to the fungal "Union" (Barr, 1992), it could not be readily placed in any existing fungal species, genus, order, class or even phylum. This enigmatic organism produced branched, septate, somatic hyphae, closely applied to, and possibly parasitizing, the hyphae or thick-walled spores of another fungus (one of the substrate fungi was tentatively identified as a Pythium sp.). Specialized spore-producing hyphae arose from the somatic hyphae. The distal two-thirds of each sporiferous hypha was closely septate. From each ofthe up to 35 short cells thus delimited arose single, lateral, finely tapering, needle-like extensions. At the tip of each extension, a single, apically pointed, ampulliform spore was produced. Significantly, during sporogenesis the entire con? tents of the sporiferous cell and of its lateral ex? tension migrated into the spore, which then seceded fairly readily, though sometimes taking with it a narrow apical fragment of the sporif? erous extension. This total evacuation of a spo? riferous cell is rare among members of the phy? lum Dikaryomycota (Ascomycotina plus Basidiomycotina), but is often seen in the protoctistan fungi (e.g., phyla Oomycota and Chytridiomycota). Although we have collected the fungus only twice and have not been able to establish it in axenic culture (spores plated out on malt extract agar failed to germinate), we consider this or? ganism to be so unusual as to be worth bringing to the attention of other mycologists. We describe a new taxon in the hope that others will rediscover it and perhaps be able to place it in an appropriate taxonomic niche.

A comparative study of the wild type A. nidulans and a mutant strain aco-T69 (lacking conidia and cleistothecia) revealed the better production of beta-1,4-glucosidase in the former. The relative distribution of the enzyme levels in various morphological structures viz. somatic hyphae, spores and cleistothecia also showed a variation. Highest specific activity was found in the cleistothecial extracts. The electrophoretic analysis of the wild type strain demonstrated the presence of three isoenzymes of beta-1,4-glucosidase i.e. beta-GLU I, beta-GLU II and beta-GLU III, the number of which varies from one to three during the growth of the organism. The parallel study of the mutant strain showed complete absence of beta-GLU II. All three forms were present in the somatic hyphae and cleistothecial extracts while spore extracts depicted the absence of beta-GLU III in the wild type.

The ultrastructure ofKineosporia aurantiaca was investigated with phosphotungstic acid negative staining and thin sectioning techniques. Motile spores were observed, each having a polar tuft of flagella. Thick-walled somatic hyphae displayed prokaryotic morphologies. Sporangia were seen having a single spore with no evidence of spore segmentation or branching. The findings were consistent with the light microscopic observations of Pagani and Parenti.

Hyphae of Geotrichum candidum Lk ex Pers. have similar extension rates and cell dimensions when grown either in steady-state glucose-limited chemostat culture or on solid media with low initial glucose concentrations. In both methods of culture the mycelium is undifferentiated and hyphal development is incomplete. In liquid media which permit full hyphal development there is a recurrent cycle of development in which each apical cell branches dichotomously when five or more nonapical cells have been produced. During each cycle there is a gradual increase in diameter and volume of the apical cell and each successive non-apical cell produced is wider and of greater volume. The mycelium is undifferentiated. The effect of temperature on cell dimensions and hyphal development is discussed for chemostat culture, batch liquid culture and culture on solid media. In most cases an increase in temperature is associated with a decrease in hyphal diameter and cell volume.

Apical cells of hyphae of Geotrichum candidum Link ex Pers. increase in width and volume as specific growth rate increases during glucose-limited chemostat culture and culture on solid media. Subapical-cell length is constant over a wide range of initial glucose concentrations on solid media but decreases with increasing specific growth rate in chemostat culture. In chemostat culture the mycelial fragments display the following trends as specific growth rate increases: the main hypha of each fragment decreases in length; the mean extension rate of the apical cells increases; more of the non-apical cells of the main hyphae form lateral branches and, ultimately, some of the subapical cells of the main hyphae form lateral branches as do some of the non-apical cells of the primary lateral branches. The length of the hyphal growth unit is constant for a range of sizes of mycelial fragments at a given specific growth rate and temperature but decreases markedly with increasing specific growth rate. The volume of the hyphal growth unit is constant over a wide range of specific growth rates at 25°C and at 30°. A model is derived for growth of G. candidum in chemostat culture at the specific growth rates and temperatures studied. The development and differentiation of somatic hyphae is discussed in relation to different culture conditions.

The life cycle of Achlya involves germination of spores to form coenocytic somatic hyphae, followed by differentiation of hyphal tips into sporangia. From germination to release of new spores occupies 27–30 h. Total lipid made up 10% of dry weight in ungerminated spores. After germination, total lipid fell to 6% of dry weight in 15 h, then rose to7.7% at the time of sporangium formation. Half of the initial loss of lipid took place within 2 h of germination. The ability of Achlya to incorporate [1-14C]acetate into lipid was maximal at the time of sporangium formation, and glycerides were the principal component of total lipid to become 14C-labelled at all stages of the life cycle. Fatty acid synthetase activity measured in cell-free extracts was low in spores and in actively elongating mycelium, but increased during differentiation to a level 15-fold greater than that in spores. Fatty acid oxidation, as estimated by the release of 14CO2 from 1-14C-labelled fatty acids, was also maximal at the time of sporangium formation.

The cells of the somatic hyphae and conidia of Helminthosporium oryzae were multinucleate. The number of nuclei in each cell varied greatly. Conidial cells contained more nuclei than hyphal cells. Hyphal fusions with subsequent nuclear migration were observed in all parts of the colony. All these results strongly indicated that the abnormally high variation rate of H. oryzae among isolates or subcultures of the same isolate may be attributable to the perpetuation of heterokaryosis as a result of the high frequency of anastomosis and nuclear division.

Perithecia of Gnomonia comari (Ascomycetes) mature within 14 days on cornmeal agar under continuous fluorescent light at 25 C. The perithecium is initiated by a coiled, multicellular ascogonium. Branches from somatic hyphae surround the ascogonium. This hyphal envelope early differentiates into two regions: a centrum of pseudoparenchymatous cells and a peripheral wall of more elongated, flattened cells. The wall produces a long, ostiolate beak by eruption of a column of hyphae from the inner layers at the apex; the cells gradually become thick-walled and brown from the peripheral layers inward. Proliferations from the ascogonial cells near the center of the perithecium form a bowl-shaped mass of ascogenous hyphae which expands centrifugally until it appears in section as a crescentic layer across the middle of the centrum. The centrum pseudoparenchyma above this incipient hymenium disintegrates, and short abortive paraphyses extend upward from the subhymenial pseudoparenchyma into the resulting cavity. The paraphyses disintegrate as the asci develop among them. The hymenium gradually pushes downward into the disintegrating subhymenial pseudoparenchyma until it rests on the perithecial wall. Maturing asci become detached from the hymenium, fill the perithecial cavity, and pass through the ostiole. At the tip of the beak they discharge their ascospores forcibly. Diaporthaceae with abortive paraphyses may occupy an intermediate position in a series leading from forms (Gaeumannomyces graminis) with long delicate paraphyses resembling those in the Sordariaceae to forms (Stegophora ulmea) in which the centrum is entirely pseudoparenchymatous.

SUMMARY: By using phase-contrast microscopy a ‘Spitzenkorper’ was seen at the hyphal apex of all the ‘septate’ fungi examined, but none was seen at the apex of any Phycomycete. The spitzenkorper accepts staining with cationic dyes. A method is described for consistently obtaining ultra-thin sections longitudinally through hyphal apices. Electron micrographs indicate that the spitzenkorper is an aggregation of vesicles just beyond the apex, namely at the region where wall-formation occurs during extension growth. It is suggested that the vesicles are formed posteriorly and migrate to the apex where they fuse with the plasma membrane liberating their contents as part of the process of wall growth.

Movement of potassium from somatic hyphae into sporangiophore initials (stages I and II) involved bulk flow induced by evapotranspiration. A progressive decrease in water uptake by the sporangiophore after stage I was associated with a decrease in permeability of the surface, particularly of the upper part of the structure. The rate of uptake of potassium declined more rapidly than water uptake, reaching a minimum during stages II and III, and subsequently increased. Distribution of potassium during the later phases of development was not uniform throughout the sporangiophore. The concentration in the apex was maintained at a constant value of approximately 125 mmol l −1 irrespective of environmental water activity, whereas the concentration in the base was higher, more variable and dependent on environmental water activity. Movement of potassium from base to apex of the sporangiophore was associated with a second type of cytoplasmic streaming which was independent of atmospheric water activity.

The Ascomycete fungus Aspergillus nidulans reproduces asexually by differentiating conidiophores and conidia. Gene regulation during asexual reproduction was investigated by comparing poly(A) RNA populations derived from somatic hyphae, conidiating cultures and purified conidia. Single-copy and complementary DNA hybridization experiments showed that vegetative cells contained 5600–6000 diverse, average-sized poly(A) RNA sequences distributed into three prevalence classes. cDNA hybridization experiments indicated that a significant proportion of the poly(A) RNA derived from either conidiating cultures or spores consisted of sequences absent from somatic hyphae. To assess accurately the degree to which the poly(A) RNA populations differed, cDNA preparations were isolated which were complementary to sequences present only in conidia or in conidiating cultures. Hybridization of these cDNAs with poly(A) RNA from conidiating cultures showed that approximately 18.5% of the poly(A) RNA mass comprised 1300 diverse sequences not present in somatic cells. Of these, about 300 were present only in conidia. The remainder were accumulated specifically during sporulation, but were absent from spores. Analogous experiments showed that the great majority of the poly(A) RNA sequences accumulated by vegetative hyphae were also present in conidiating cultures. Thus, cell differentiation during A. nidulans asexual reproduction involves the accumulation of many new poly(A) RNA sequences, but not the loss of preexisting ones.

There are four chromosomes present in the somatic nuclei of Trichophyton mentagrophytes. Initially, these chromosomes are ring-shaped but as division proceeds they unfurl becoming rod-like. The spindle apparatus appears to be strand-like and beaded. At mid-division the chromosomes lie in two rows parallel to each other and on either side of the spindle. Each row contains four chromosomes which appear to be attached to the spindle at regions along its length. At the end of division each sister nucleus contains a complement of four chromosomes. Movement of sister nuclei at the end of division appears to be unipolar. The single nucleolus in T. mentagrophytes does not disappear from view during division or immediately after separation of sister nuclei. As a result this nucleolus has been designated as an "undivided persistent nucleolus."

Nuclei of twelve Einericellopsis entities were successfully demonstrated by staining with HCI-Giemsa following treatment in 0.002 M 8-hydroxyquinoline and fixation in Carnoy's with chloroform. The hyphal cells of all known species of Emericellopsis were demonstrated to be uninucleate, with the exception of Emericellopsis synnematicola where binucleate cells were also observed. Conidia and ascospores were found to be uninucleate, thus confirming primary homothallism, as often suggested by the culturing of single spores. In some species, a high frequency of anastomosis and migrating nuclei reflected a means of establishing heterokaryons. It was observed that interphase nuclei, typically elliptical, were extremely elongate near hyphal tips. The presence of chromatin bodies (2-4 per haploid nucleus) and division figures suggested a mitotic mode of division in the somatic hyphae of Emericellopsis. The ascomycetous genus Emericellopsis was established in 1940, (van Beyma Thoe Kingma), when two species were described. Seven additional species have now been described and a number of unidentified isolates of Emericellopsis have been reported (Benson, 1966). Since the original description of the genus relatively little has been done to elucidate the nuclear situation. The nuclear staining procedures employed on Emericellopsis by Elander (1960) and Fantini (1962) served as adjuncts to their major research efforts and were limited to a small number of species. In both cases nuclear detail was lacking and ascospore nuclei were not observed. In this study numerous fixing and staining techniques were employed with hyphae, conidia, and ascospores of Emericellopsis species in an attempt to give a more complete picture of the nuclear situation and to provide evidence for the type of homothallism present in this

Sporulation of somatic hyphae of G. candidum Link can be induced by the presence of an older colony of the same species, or of another species. Self-induction may occur where there is a relatively large amount of fungal material included in a limited volume of medium. Sporulation can also be induced in sporelings at an early stage of development. Evidence is presented that the induction is due to a diffusible fungal metabolite or to a depletion of a factor essential for maintenance of the somatic phase. Above critical nutrient levels of carbon source and nitrogen source the somatic state can be maintained even under conditions which otherwise induce sporulation. A hypothesis is proposed based on a switch between two metabolic conditions, one leading to the somatic phase, the other to the arthrospore phase. Successful induction, on this hypothesis, involves an interference with the metabolic condition characteristic of the somatic phase. In the presence of sufficient exogenous carbon and nitrogen sources the inducing effect is counterbalanced and does not lead to sporulation.