Fungi: Plant Pathogenic

A.B. Gould , in Encyclopedia of Microbiology (Third Edition), 2009

Zygomycota

The Zygomycota are terrestrial fungi with a well-developed, coenocytic, haploid mycelium. The thallus is haploid, and chitin and chitosan are significant constituents of the hyphal cell wall. Asexual reproduction in the zygomycetes results in nonmotile spores called sporangiospores. Sexual spores, or zygospores, are produced when two morphologically similar gametangia of opposite mating types fuse. These fungi are saprophytes or weak pathogens, causing postharvest molds and soft rots. For example, some species of Mucor are soil inhabitants that penetrate fruit (through wounds or at the calyx) that have fallen to the orchard floor. Within two months of cold storage, the fruit are completely decayed and fungal mycelium emerges in tufts through the cuticle.

Although R. stolonifer is best recognized as the common bread mold, under the right circumstances, this ubiquitous saprophyte also causes a soft rot of fleshy fruit and vegetables, bulbs, corms, flowers, and seeds. The thallus consists of hyphal structures known as rhizoids (short branches of hyphae that resemble roots), which penetrate the food substrate, and stolons (longer branches of hyphae) that skip over the substratum surface. The fungus produces asexual sporangiospores (also called mitospores) that form on the swollen tip (columella) of a long aerial sporangiophore. The fungus is heterothallic; as its food supply is depleted, isogametes of opposite mating type fuse to form a zygosporangium containing a single heterokaryotic zygospore. After a 1–3 month period of dormancy, the zygospore undergoes meiosis to form four haploid nuclei (two of each mating type) and germinates to form a sporangium. Sporangiospores are formed by mitosis; these spores are homokaryotic; one-half of the spores are of one mating type, and the other half are of the opposite mating type.

The soft rot disease process begins as sporangiospores, ubiquitous in the air, penetrate through wounds in various plant parts. Cellulase and pectinase enzymes, produced by the fungus, degrade the middle lamella and cell walls of plant tissues, causing a soft, water-soaked rot. The nutrients released are used by the fungus to produce fluffy tufts of a gray/brown aerial mycelium consisting of fungal hyphae and fruiting structures. Eventually, moisture is lost from the degraded tissue, which becomes firm and mummy-like.

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FUNGI | Classification of Zygomycetes

K. Voigt , P.M. Kirk , in Encyclopedia of Food Microbiology (Second Edition), 2014

Morphological Considerations: Which Structures Exhibit Phylogenetic Relevance?

The phylum Zygomycota represents a heterogenous group of mainly saprobes, usually found in the soil or in association with plants, fungi, animals, or humans as opportunistic pathogens. In addition, some are facultative or obligate parasites, the latter especially of arthropod and fungal hosts. Many are among the most widely distributed of the fungi, ubiquitously occurring in all climatic zones of the Earth's biosphere. With respect to numbers of described species, the group is relatively small, with some 160 genera and 1050 species compared with, for example, the Basidiornycota, which has more than 31 515 species, and the Ascomycota with more than 64 163 species ( Kirk et al., 2008).

The Zygomycota are characterized by an asexual propagation based on aplanate mitospores – sporangiospores – of endogenous origin (Benjamin, 1979). The sporangiospores are formed within multispored sporangia or few-spored to single-spored sporangiola borne on branched or unbranched aerial sporangiophores. Micromorphologically discriminative criteria are mitotic structures variable in shape, ranging from large multispored (>1000 spores) sporangia borne on tall (c.12 cm) sporangiophores to single-spored sporangiola, or rarely multispored but uniseriate sporangia (merosporangia), borne on simple, unspecialized sporangiophores. The single-spored sporangiolum, in addition, may be found associated with rather complexly branched sporangiophores. The multispored condition has been presumed to be the most primitive and the single-spored condition the more advanced, but there is no clear evidence for this. The sporangiospore is presumed to be a spore of dispersal and colonization of suitable substrata, ranging from soil to specific substrata like tissues of plants, animals, or mycelia of fungal hosts. The sexual stage is the zygospore, which forms between a pair of yoke-shaped suspensors (supporting hyphae remaining after the delimitation and fusion of the gametangia), from which the names of the taxonomic groups (phylum and class) were derived. The modification of hyphae to form zygophores, often also termed progametangia, occurs in heterothallic and homothallic species, in response to chemical stimulants, trisporic acid, and its derivatives, resulting from degradation of beta carotene. The suspensors may be either opposed (on opposite sides of the zygospore) or apposed (lying almost parallel) or, rarely, tongslike. The suspensors sometimes are ornamented with hyphallike or antlerlike outgrowth. During the course of zygosporogenesis, the zygospore is formed as a result of hyphal conjugation followed by fusion of gametangia (gametangiogamy). Thick-walled, ornamented (in the form of warts or spines), and melanin-pigmented zygospores are considered to be primitive. In the presumed advanced forms, the zygospore typically is thin walled, and the wall is not pigmented (or just lightly pigmented) and smooth (or only slightly ornamented). Intermediate forms have varying degrees of wall thickening, pigmentation, and ornamentation. Zygospores are unknown in many species of zygosporic fungi, which otherwise are included in the group because of the characters of their asexual structures. The heterothallic condition is predominant in species where zygospores are known; the homothallic condition is somewhat restricted in occurrence. The zygospore has evolved as a spore of survival. Once formed, zygospores rarely germinate, suggesting a low selective pressure for dispersal and genetic stability via meiotic recombination to ensure survival and successful establishment within competitive microbial communities.

Phylogenetic reconstructions of their evolution based on multigene sequence data provide evidence for a decreasing importance of zygospore formation in their evolution. Although the most basal genera (e.g., Basidiobolus within the Entomophthorales, Lentamyces – part of Absidia sensu lato – within the Mucorales) within given orders reliably produce zygospores, it is likely that the derived genera almost lost their ability to produce zygospores. On the other hand, asexual sporangiospores are produced in many of the species of the group. Contrary to the decreasing incidence of zygospores, a raise of quantity, efficiency, and longevity of mitospores is observed toward the derived lineages. For example, members of the genera Rhizopus and Rhizomucor produce rhizoids, hyphal outgrowths primarily at the base of the sporangiophores and serving as multiplier for sporangium-bearing sporangiophores, which provides advantageous dispersal over the nonrhizoidal genera among the Mucorales. As a consequence of this reciprocal development among asexual and sexual spore formations, the zygosporic fungi appear to develop apart from sexual dispersal toward clonal dispersal during the course of evolution. Thick-walled (rough) zygospores are considered to be primitive, as is the case for the Entomophthorales and Mucorales. Thin-walled (smooth) zygospores are known to be advanced, as is the case in the majority of members of the Dimargaritales, Eccrinales, Harpellales, Kickxellales (Kickxellomycotina), and Zoopagales (Zoopagomycotina).

The search for criteria (ultrastructural, physiological, chemical, molecular, and so on) that are suitable as synapomorphic characters is suggested to circumscribe the Zygomycota as distinct taxon and its subgroups at all taxonomic levels. Apart from morphological identification, much progress was achieved to establish a molecular identification of zygomycetes based on suitable molecular barcode markers, with an emphasis on the Mucorales and the Mortierellales (Hoffmann et al., 2009; Hoffmann and Voigt, 2011; Papp et al., 2011; Petkovits et al., 2011; Liu and Voigt, 2011). The use of the nuclear internal transcribed spacer ITS1 and ITS interrupted by the 5.8S ribosomal DNA was found to be highly suitable for the zygomycetes and also was chosen to be the universal barcode marker for all fungi and highly suitable for the zygomycetes (Schoch et al., 2012).

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Control

M.S. Goettel , ... T. Glare , in Comprehensive Molecular Insect Science, 2005

6.11.2.3 Phylum Zygomycota

Traditionally, the Zygomycota are separated on the basis of often nonseptate, multinuclear hyphae, and production of zygospores by copulation between gametangia. However, molecular analyses have not found the Zygomycota to be monophyletic ( Jensen et al., 1998), and some groups, such as the Glomales, may be placed elsewhere eventually (e.g., Bruns et al., 1993). Basidiobolus ranarum and other Basidiobolus species, traditionally considered as Zygomycetes, have now been placed in the Chytridiomycetes, despite being nonflagellate (Nagahama et al., 1995).

Within the true Zygomycota, the class Trichomycetes contains species often associated with insects. While Sweeney (1981) described the species Smittium morbosum (Trichomycetes) as a pathogen of mosquitoes, most associations of the Trichomycetes are symbiotic or weakly parasitic rather than true pathogens (Beard and Adler, 2002; Cafaro, 2002). Some species of Mucor (Mucorales) are occasionally associated with insect mortality.

The majority of entomopathogenic species within Zygomycota are contained in one order, the Entomophthorales. More than 200 entomopathogenic Entomophthorales species have been recognized. They commonly cause spectacular epizootics and are characterized in all genera but one (Massospora), by the production of forcibly discharged primary conidia. Many species are capable of producing various types of secondary conidia from the primary conidia and, in some cases, infection is obligatorily through a secondary conidium. Many species are also capable of producing resting spores, long-lived zygospores or azygospores. These fungi are generally obligate pathogens in nature, and many species are presently difficult or impossible to culture on artificial media.

Until around the 1960s, most entomopathogenic Entomophthorales were contained within a single genus, Entomophthora, but several years of taxonomic revision have placed the species into several genera. The main genera containing entomopathogenic species are Conidiobolus, Entomophaga, Entomophthora, Erynia, Furia, Massospora, Neozygites, Pandora, Strongwellsea, and Zoophthora.

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Fungi

Thomas J. Volk , in Encyclopedia of Biodiversity (Second Edition), 2013

Zygomycota

Commonly called the bread molds, the Zygomycota are terrestrial fungi whose fruiting bodies are mostly microscopic in nature, although their asexually produced sporangia can reach greater than 5  cm tall in some species (Figure 3). Under certain conditions they may sexually produce thick-walled resting spores called zygospores (Figure 4). Some, such as Rhizopus, Mucor, and Phycomyces, can grow on a wide variety of substrates, and a few can act as human pathogens. Many species, such as Pilobolus, inhabit dung and pass through the guts of herbivores to get into more dung.

Figure 3. Rhizopus sporangia.

Figure 4. Rhizopus zygospore between suspensors.

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Fungi

Thomas J. Volk , in Encyclopedia of Biodiversity, 2001

IV.B.2. Zygomycota

Commonly called the bread molds, the Zygomycota are terrestrial fungi whose fruiting bodies are mostly microscopic in nature, although their asexually produced sporangia can reach greater than 5  cm tall in some species (Fig. 3). Under certain conditions they may sexually produce thick-walled resting spores called zygospores (Fig. 4). Some, such as Rhizopus, Mucor, and Phycomyces, can grow on a wide variety of substrates, and a few can act as human pathogens. Most importantly, members of one order, the Glomales, are responsible for forming mutualistic associations called endomycorrhizae with the roots of about 70% of the world's plants. Ectomycorrhizae (from Basidiomycota and Ascomycota) form with another 20% of plant species. See Section V,D,1 for further discussion of mycorrhizae.

Figure 3. Rhizopus sporangia.

Figure 4. Syzygites zygospore between suspensors.

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Rhizopus stolonifer (Soft Rot)

Silvia Bautista-Baños , ... Laura L. Barrera-Necha , in Postharvest Decay, 2014

Concluding Remarks

Rhizopus stolonifer is a common member of the fungal phylum Zygomycota. It plays a key role in the carbon cycle because it works as a decomposer in soil, dung and discarded foods, it has also been reported to have medicinal properties. However, for the wholesale and retail business market, R. stolonifer is considered one of the most destructive fungi. The importance of R. stolonifer lies in its fast growth (it is considered the fastest-growing fungus) and its wide array of hosts, as it affects numerous horticultural commodities worldwide. Generally, R. stolonifer is acquired during the first steps of the postharvest chain; harvest and handling in the packing house. Other commodities such as strawberries and tomatoes may be infected before harvest. It is also known that R. stolonifer inoculum may be present on plant organs such as leaves and fruitlets, but few studies about what direct preharvest actions might be implemented to reduce the incidence of this fungus at this stage have been carried out.

There are numerous alternative methods for controlling Rhizopus rot during postharvest. Among the conventional ones, the most predominant action is the application of synthetic fungicides. In this respect, fungicides such as Benlate®, Rovral® and Botran® have serious limitation on their application in some countries, while others labeled as reduced-risk fungicides, including Boscalid, as well as Fluodixonil and Fenhexamid, have obtained clearance from the US Environmental Protection Agency (EPA). Currently, most fungicides are listed as 'slightly hazardous' to human health, and they may also enter the water, soil and air; therefore, care must be taken with their selection. In addition, the decision on whether to use fungicide is taken based on the target market.

Today, there is strong public resistance to consuming chemically treated horticultural commodities. As a result, the postharvest control of diseases has taken on new aims, i.e. developing products that are less harmful to human health and the environment. For controlling R. stolonifer, research on the development of alternative methods has also been intensified. The most extensive studies have been conducted on the use of antagonists although their registration and acceptance is difficult since the mode of action is unclear. To our knowledge, there are only a few commercial products available for controlling R. stolonifer, namely Biosave®, 10LP, 11LP and Shemer®.

Based on the information gathered, other extensively tested alternative methods include plant extracts and essential oils. Although most published information has been focused on in vitro studies, those evaluations carried out with these methods on horticultural commodities resulted in adequate control of this fungus. Further evaluations at a commercial level should be considered with thyme, oregano and cinnamon essential oils. Unfortunately, information about commercial products based on plant derivatives and used against R. stolonifer has not been published. With respect to UV-C irradiation, results are encouraging since significant control has been achieved with this technology; however, due to its high costs and unknown side effects, which have led to public concern, its future remains in doubt. Future research with the trend focused on better combined formulations based not only on the individual properties of the substances but also on their proportion and chemical compatibilities with chitosan and waxes is needed. To date, these technologies, together with UV-C irradiation and hypobaric atmospheres, not only may have fungicidal potential but also enhance the induction of resistance mechanisms in fruits and vegetables against R. stolonifer. Enzymatic defense activities including PAL, chitinase, POD and a β-1, 3-glucanase are reported to be involved in the reduction of R. stolonifer during the infection process.

Studies looking at combining fungicides at lower concentrations with other non-chemical alternatives such as essential oils, waxes, and antagonists have been undertaken, resulting in substantial control of R. stolonifer. According to the published results, they may soon be commercially available.

The reported postharvest technologies to control R. stolonifer seem to hold considerable promise in terms of reducing postharvest losses caused by this fungus. And, as with any other new technology, the overall impact should be assessed not only in the fruit itself and, in this case, on R. stolonifer, but also on an application system for harvesting, transport, packaging and store retail operations.

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Reprogramming the Genome: Applications of CRISPR-Cas in Non-mammalian Systems Part A

Takayuki Arazoe , in Progress in Molecular Biology and Translational Science, 2021

1 Introduction

The kingdom Fungi contains five major phyla: Chytridiomycota, Zygomycota, Ascomycota, Basidiomycota, and Glomeromycota. Fungi are a highly complex group of eukaryotic microbes that play a crucial role as decomposers and maintain ecological balance by recycling carbon and other elements. Fungi comprise three major groups, single-celled yeasts, multicellular filamentous molds, and macroscopic filamentous fungi (mushrooms), based on their morphogenesis and life cycles. 1 The budding yeast, Saccharomyces cerevisiae, multiplies by budding, in which a daughter cell pinches or buds from the parent cell. S. cerevisiae has long been used in fermented food and beverage production, and as a cell factory for a wide range of bioproducts, such as ethanol, building block chemicals and oil. 1 Filamentous fungi, including molds and mushrooms, form a multicellular tubular structure called hyphae. Hyphae grow by apical extension, and the mycelium is formed by aggregated hyphae. In macroscopic filamentous fungi, visible fruiting bodies (mushrooms) holding spores are made of mycelium, and some of them are edible. Some filamentous fungi are employed in the food, agricultural, and pharmaceutical industries, and are used for the cell factory of organic acids, ethanol, fatty acids, enzymes, antibiotics and pigments. 1,2 Conversely, fungi also include various plant, human, and animal pathogens.

Throughout history, plant disease epidemics caused by fungi and fungus-like oomycetes have posed a worldwide threat to food safety. For example, in the 19th century, the potato late blight disease caused by the oomycete Phytophthpra infestans triggered the Irish potato famine, which resulted in the death of more than 1 million people, and many more were forced to emigrate to escape poverty and starvation. 3 In the 20th century, the ascomycete fungus Cryphonectria parasitica (formerly Endothia parasitica), a causal agent of chestnut blight, led to devastating disease epidemics on native tree species. Due to these epidemics, the American chestnut has largely been eliminated in North America, and the European chestnut has been rapidly declining in Europe. 4 Interestingly, mycovirus-attenuated C. parasitica was isolated, which could be used as a biological control agent of chestnut blight in Europe. 5

The most common human fungal diseases are responsible for superficial infections, and approximately a billion people are estimated to have cutaneous fungal infections. 6 Fungal diseases show high mortality rates, and it is estimated that fungal pathogens cause more than 1.6 million people deaths annually. Unlike bacteria, owing to the close evolutionary relationship between fungal pathogens and humans, the identification of effective drug targets in fungal pathogens that are non-toxic to human is still challenging. Indeed, emerging drug-resistant mutants are a serious problem for fungal disease treatments. Therefore, the antifungal drug treatment of fungal infections is limited, and fungal pathogens are increasingly recognized as a major threat to humans. 6,7

Pathogenic fungi affect not only plants and humans but also diverse groups of animals. For example, the skin-infecting amphibian fungus Batrachochytrium dendrobatidis causes chytridiomycosis in amphibians. Chytridiomycosis resulted in the decline of at least 501 amphibian species, including 90 presumed extinctions in 54 countries. 8,9 Over 40% of amphibian species are lost in some areas of Central America, and the reduction in amphibian diversity is ongoing worldwide. 9,10 A decline in other animal populations caused by fungal pathogens has been observed across diverse taxa, including bats, soft corals, bees, and fish. Therefore, animal fungal pathogens also cause attrition of biodiversity and ecosystem health. 9

In this context, a simple yet efficient genetic manipulation method for large-scale genetic analysis could facilitate further understanding of the basic biology, virulence factors, infection mechanisms, drug resistance mechanisms, and host-pathogen interactions, which are critical for developing novel strategies to combat fungal pathogens. Besides, the rapid genetic engineering of hosts and biological control agents without the insertion of foreign DNA, which enables molecular breeding without generating genetically modified organisms (GMO), would be a powerful strategy to combat fungal disease epidemics. Owing to the emergence of RNA-guided programmable nuclease CRISPR/Cas9, which was developed from bacterial adaptive immune systems, genome editing has revolutionized the ability to perform large-scale genetic analyses, including multiplex, marker-free, and precise genome manipulation. CRISPR/Cas9 comprises a Cas9 endonuclease and single-guide (sg) RNA, which is a synthetic fusion of the CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA). 11 The Cas9/sgRNA ribonucleoprotein (RNP) complex can recognize and bind the target DNA sequence (generally 20 nucleotides) by forming an sgRNA (spacer)/target DNA (protospacer) hybrid structure 12 (Fig. 1). The complex displaces the non-complementary strand of the target DNA (R-loop structure), and the RuvC and HNH nuclease domain of Cas9 cut the single-stranded DNA at the R-loop structure. Besides, the nuclease-deficient Cas9 with mutations in the RuvC domain (D10A) and/or HNH domain (H840A) can be used as the single-stranded nuclease (nCas9) and DNA binding proteins (dCas9). Furthermore, nCas9 or dCas9 fused to effective proteins allows for the development of applications such as base editing, CRISPR interference (CRISPRi: downregulation of the target gene), and CRISPR activation (upregulation of the target gene) 12 (Fig. 1). One limitation of the CRISPR system is the protospacer-adjacent motif (PAM). In the case of the Cas9 from S. pyogenes (SpCas9), 5′-NGG-3′ is required downstream of the target sequence (Fig. 1). Although spCas9-meidated genome editing is mainly used for pathogenic fungi, other types of CRISPR systems have begun to be optimized for filamentous fungi (see Section 4).

Fig. 1

Fig. 1. Schematic overview of applicable genome editing technology and strategy in pathogenic fungi. Pol III promoter: polymerase III dependent promoter such as U6; Pol II: polymerase II dependent promoter such as constitutive promoters for strong expressions; NLS: nuclear localization signal; Pro.: promoter; Term: terminator; NHEJ: non-homologous end joinin; HR: homologous recombination; SST-R: single-stranded template repair; crRNA: crisprRNA; PmCDA1: cytidine deaminase derived from sea lamprey; UGI: uracil glycosirase inhibitor; Rta, P65, and VP64: transcription activation domain.

The fundamental genome editing strategy relies on inducing DNA double-strand break (DSB) repairs at the target locus by CRISPR/Cas9 and other programmable nucleases. In eukaryotes including pathogenic fungi, DSBs are repaired by two main pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). NHEJ-mediated genome editing can induce insertions and/or deletions (indels) at the target site without donor DNA. Therefore, this strategy is effective for targeted gene disruptions in host cells with low HR efficiency, but the mutation type cannot be designed (Fig. 1). HR-mediated genome editing can induce more precise and desired mutations, such as targeted gene knock-out, knock-in, and replacement, by using donor DNA templates; however, the construction is often laborious, and the HR efficiency depends on the species and cell types. 13 In contrast to animals and plants, HR-mediated genome editing can be efficiently induced by specific DSB in many pathogenic fungi (filamentous fungi). Meanwhile, NHEJ-mediated genome editing is often inefficient in some fungi (filamentous ascomycetes) due to some other escape mechanisms, which results in the inactivation of CRISPR/Cas9 or appearance of escape strains. This escape mechanism has prevented the development of genome editing technology in filamentous fungi (filamentous ascomycetes), including high-throughput gene disruption, targeted gene regulation and epigenome editing. It has also been reported that introducing excessive DSB without the donor DNA tends to cause large deletions in some filamentous fungi. 14,15 Therefore, additional and original modifications may be required for genome editing in each pathogenic fungus.

In this chapter, I have summarized two topics: "Genome editing in plant pathogenic fungi and fungal-like oomycetes" and "Genome editing in human and animal pathogenic fungi." Following these topics, I have analyzed key considerations to conduct genome editing and discussed applications in basic research as well as control of pathogenic fungi.

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Diagnosis of Parasitic and Nonparasitic Diseases

Dominique Blancard , in Tomato Diseases (Second Edition), 2012

Rhizopus stolonifer (Ehrenb.) Vuill. (syn. Rhizopus nigricans Ehrenb. [Rhizopus rot ])

Rhizopus , Mucoraceae, Mucorales, Incertae sedis, Zygomycetes, Zygomycota, Fungi

Symptoms Moist and soft lesions expanding rapidly mainly on ripe fruits. The affected tissues liquefy and eventually collapse, the cuticle splits (Photo 788). Exudation of juice may be found. The fungus mycelium invades the tissues which are covered by a whitish grey mould. This mould is formed by the mycelium, sporocystophores, and sporocysts of this Zygomycete (Photos 789 and 790, Figure 53). Ultimately, many fructifications, ‘black pinheads’ form on the damaged tissues (Photo 789).
Biology This ubiquitous saprophytic fungus grows very easily on and in soil, on plant debris of many types, on various wet and dry substrates, and remains there for several years sometimes in different forms: spores, chlamydospores, zygospores, mycelium. It is also known to induce rot on many plant species, notably fruit and vegetables. It is thus present in the plants environment in the fields and stores, on the packaging and storage materials. It enters fruits through various wounds, but also from the stylar and peduncular scars. Once in the tissues, it invades them, quickly rotting them, and eventually sporulates on the surface with many sporangiophores containing countless black spores in sporangia. These spores are spread by wind over long distances, but also by splashing water, by workers and some ‘passive vector’ insects, including Drosophila melanogaster (Photo 793). Contact transmission of rotten fruit to healthy fruit is also possible.
Wet weather and the high temperatures during summer are very favourable for Rhizopus stolonifer development. Thus, it thrives at temperatures of around 23-27°C and high humidity. It also occurs at low temperature during fruit storage. Ripe tomatoes are particularly sensitive.

In addition to Rhizopus spp. the Mucorales includes other genera likely to attack tomatoes. This is particularly true of the genus Mucor which includes some species that can grow on tomato fruits: M. hiemalis Wehmer, M. circinelloides Tiegh. The rot they cause and the mould that covers them are quite comparable to those produced by R. stolonifer. They are moist and soft (Photo 791) and covered with a greyish fluffy mould (Photo 792). Their biological characteristics are similar to those of Rhizopus.

788

788. The ripe fruit is fully degraded by a wet and soft rot. The liquefied tissues have collapsed and the skin has broken and shrivelled in places. An aerial black mould has grown in the cracks.

Rhizopus stolonifer

789

789. This mould is formed by the aseptate mycelium of Rhizopus stolonifer. Many black spherical sporangia on rigid sporangiophores can be seen. They are hyaline before gradually browning.

790

790. The use of a microscope shows the columella, the rhizoids, and numerous brownish spores of this Mucoraceous fungus.

Rhizopus stolonifer

791

791. Generalized wet rot on this ripe fruit. The flesh has liquefied and the skin is wrinkled. A greyish aerial mould develops around the peduncle and the stylar end.

Mucor sp.
Unlabelled Image

Mucoraceous rots (Mucor and Rhizopus rot)

792

792. As for Rhizopus, Mucor produce spherical sporangia at the end of straight sporangiophores. A young evolving sporangium is clearly visible.

Mucor sp.

793

793. Many small flies (Drosophila melanogaster) dot this fruit, rotting with a Mucoraceous fungus.

Figure 53

Figure 53. Drawing of Rhizopus stolonifer fructifications.

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SEQUESTRATE FUNGI

MICHAEL A. CASTELLANO , ... DANIEL L. LUOMA , in Biodiversity of Fungi, 2004

SYNOPSIS OF TAXA

Sequestrate fungi occur in two phyla of the Kingdom Eumycota: the Zygomycota (in the class Zygomycetes) and the Dikaryomycota (in classes Ascomycetes and Holobasidiomycetes). Presently recognized genera are listed in Table 10.1 by order and family. Assignments of genera to families differ in many cases from previous placements (e.g., Trappe 1979; Jülich 1981; Castellano et al. 1989; Trappe and Castellano 1991) because more recent data from additional collections or DNA studies have provided new insights into phylogeny. In many cases, the family to which a genus belongs is uncertain based on morphological data alone. Studies of ultrastructure and DNA are providing new evidence that is helping to resolve many of the uncertainties, but that work has only begun (O'Donnell et al. 1996). All taxonomic decisions are hypotheses that are tested repeatedly and sometimes refuted. Some genera do not fit into any described family and are listed under the heading "uncertain status." We are aware of many undescribed genera that are not included in our compilation.

TABLE 10.1. Genera and Families of Sequestrate Fungi in the Kingdom Eumycota, by Class and Order

Phylum Zygomycota
Class Zycomycetes
 Order ENDOGONALES: Endogonaceae: Endogone
 Order GLOMALES: Glomaceae: Glomus, Sclerocystis
 Order MUCORALES: Mortierellaceae: Modicella
Phylum Dikaryomycota
Class Ascomycetes
 Order ELAPHOMYCETALES: Elaphomycetaceae: Elaphomyces
 Order GLAZIELLALES: Glaziellaceae: Glaziella
 Order PEZIZALES: Ascobolaceae: Muciturbo; Carbomycetaceae: Carbomyces; Helvellaceae: Balsamia, Barssia; Humariaceae: Geopora, Hydnocystis, Phaeangium, Stephensia; Discinaceae: Hydnotrya; Otidiaceae: Genea, Genabea, Paurocotylis, Picoa, Sphaerosoma; Pezizaceae: Amylascus, Cazia, Hydnoplicata, Hydnotryopsis, Mycoclelandia, Pachyphloeus, Ruhlandiella, Sphaerozone, Tirmania; Tuberaceae: Choiromyces, Delastria, Dingleya, Hydnobolites, Labyrinthomyces, Loculotuber, Paradoxa, Reddellomyces, Terfezia, Tuber
 UNCERTAIN STATUS: Fischerula: Leucangium: Petchiomyces
Class Homobasidiomycetes
 Order AGARICALES: Agaricaceae: Endoptychum; Amanitaceae: Torrendia; Bolbitiaceae: Agrogaster; Coprinaceae: Gasteroagaricoides, Podaxis; Cortinariaceae: Cortinarius, Cortinomyces, Descomyces, Destuntzia, Hymenogaster, Kjeldsenia, Quadrispora, Setchelliogaster, Thaxterogaster; Cribbiaceae: Cribbia; Entolomataceae: Rhodogaster, Richoniella; Lepiotaceae: Neosecotium, Notholepiota; Octavianinaceae: Octavianina; Russulaceae: Arcangeliella, Cystangium, Gymnomyces, Macowanites, Zelleromyces; Strophariaceae: Nivatogastrium, Tympanella, Weraroa; Tricholomataceae: Hydnangium, Podohydnangium, Gigasperma
 Order BOLETALES: Boletaceae: Alpova, Amogaster, Gastroboletus, Gastroleccinum, Gastrosuillus, Hallingia, Melanogaster, Rhizopogon, Royoungia, Truncocolumella; Gomphidiaceae: Brauniellula, Gomphogaster; Paxillaceae: Austrogaster, Gymnopaxillus, Paxillogaster, Singeromyces; Strobilomycetaceae: Austrogautieria, Chamonixia, Gautieria, Mycoamaranthus, Rhodactina, Timgrovea, Wakefieldia
 Order GASTROSPORIALES: Gastrosporiaceae: Gastrosporium
 Order LEUCOGASTRALES: Leucogastraceae: Leucogaster, Leucophleps
 Order LINDTNERIALES: Stephanosporaceae: Stephanospora
 Order LYCOPERDALES: Geastraceae: Pyrenogaster, Radiigera Mesophelliaceae: Andebbia, Castoreum, Gummiglobus, Malajczukia, Mesophellia, Nothocastoreum
 Order PHALLALES: Clathraceae: Protubera; Gelopellaceae: Gelopellis, Phallobata, Phallogaster; Hysterangiaceae: Chondrogaster, Claustula, Gallacea, Hysterangium, Phlebogaster, Rhopalogaster, Trappea
 Order SCLERODERMATALES: Sclerodermataceae: Horakiella, Scleroderma; Sedeculaceae: Sedecula
 Order TREMELLOGASTRALES: Tremellogastraceae: Clathrogaster, Tremellogaster
 UNCERTAIN STATUS: Brauniella, Hysterogaster, Mycolevis, Protogautieria, Sclerogaster, Smithiogaster

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FUNGAL PARASITES AND PREDATORS OF ROTIFERS, NEMATODES, AND OTHER INVERTEBRATES

GEORGE L. BARRON , in Biodiversity of Fungi, 2004

APPENDIX B KEY TO THE GENERA OF FUNGI ENDOPARASITIC ON NEMATODES

1.

Living hyphae or thallus nonseptate (Oomycota, Chytridiomycota, Zygomycota) 2

1.

Living hyphae septate (Anamorph Fungi) 16

2.

Sporangia produce motile zoospores 3

2.

Zoospores absent 11

3.

Zoospores with a single posterior flagellum 4

3.

Zoospores biflagellate 8

4.

Thallus epibiotic, attached to host by rhizoids 5

4.

Thallus endobiotic 6

5.

Rhizoids originating from penetration bulb Phlyctochytrium

5.

Rhizoids arising directly from thallus Rhizophydium

6.

Thallus lacking rhizoids Olpidium (Fig. 19.4D)

6.

Thallus with rhizoids 7

7.

Thallus monocentric Endochytrium

7.

Thallus polycentric Catenaria (Fig. 19.4G)

8.

Infection resulting in a swollen, unicellular thallus Haptoglossa (Fig. 19.4J)

8.

Infection resulting in multicellular thallus 9

9.

Thallus forming a linear series of swollen segments Myzocytium (Fig. 19.4F)

9.

Thallus hyphal 10

10.

Hyphae less than 4 µm in diameter Pythium

10.

Hyphae more than 5 µm in diameter Lagenidium

11.

Mycelial infection forming chain of swollen segments 12

11.

Fungus forms hyphae or hyphallike structures 14

12.

Spores produced on erect, aerial sporangiophores 13

12.

Spores produced in sporangia, expelled through exit tubes Protascus

13.

Spores borne in apical cluster on sporangiophore Gonimochaete (Fig. 19.4F)

13.

Spores borne in succession from corkscrew apex of sporangiophore Meristacrum

14.

Hyphae nonseptate 15

14.

Hyphae septate 17

15.

Spores small (±10 µm) Euryancale

15.

Spores very large (more than 40 µm) 16

16.

Spores in apical cluster on vesicle Rhopalomyces (Fig. 19.1D)

16.

Spores in helicoid chain Helicocephalum

17.

Hyphae with clamps at septa Nematoctonus (Fig. 19.4H)

17.

Hyphae lacking clamps 18

18.

Conidiophores lacking, conidia arise directly from conidiogenous cell 19

18.

Conidiophores present 21

19.

Conidia thick-walled, spherical, pigmented Botryotrichum

19.

Conidia thin-walled, colorless 20

20.

Conidia lens-shaped, from phialides on hyphae outside host Hirsutella

20.

Conidia spherical, borne on phialides produced inside host Plesiospora

21.

Conidia several-celled Haptocara

21.

Conidia one-celled 22

22.

Conidiogenous cells aphanophialides, conidia teardrop-shaped Drechmeria (Fig. 19.4C)

22.

Conidiogenous cell globose to subglobose or flask-shaped 23

23.

Conidia with odd, helical, or fusiform shapes; ingested by nematode Harposporium (Fig. 19.4A)

23.

Conidia globose, elliptical, or wedge-shaped; adhering to cuticle Verticillium (Fig. 19.4H)

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