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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.

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.

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.

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