Mycology Unit-4 - True Fungi (PDF)

AG-MCCP4114 General Mycology Instructor: Kristy Amor A. Garcia Course Content 1. Introduction 2. Morphology, growth & reproduction 3. Pseudofungi 4. True fungi (Eumycota) 1. Phylum Chytridiomycota 2. Phylum Blastocladiomycota 3. Phylum Neocallimastigomycota...

AG-MCCP4114 General Mycology Instructor: Kristy Amor A. Garcia Course Content 1. Introduction 2. Morphology, growth & reproduction 3. Pseudofungi 4. True fungi (Eumycota) 1. Phylum Chytridiomycota 2. Phylum Blastocladiomycota 3. Phylum Neocallimastigomycota 4. Phylum Zygomycota 5. Phylum Glomeromycota 6. Phylum Microsporidia 7. Phylum Ascomycota 8. Phylum Basidiomycota 5. Fungal diseases of crops 6. Fungi as agents of biological control 4.0 True fungi (Kingdom Fungi or Eumycota) Kingdom Eumycota was for many years assumed to be made up of only four phyla—Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota. The main characteristic of this group is that they produce mycelium, the walls of which contain glucans and chitin, and they lack chloroplasts. Some fungi can produce cells that swim by means of one or two flagella. Five phyla—Hyphochytriomycota, Oomycota, Chytridiomycota, Blastocladiomycota, and Neocallimastigomycota—fall into this category. The first two are chromistan in origin while the last three are eumycotan. Microsporidia, Zygomycota, Cryptomycota, Glomeromycota, Ascomycota, and Basidiomycota—make up the rest of kingdom Eumycota and do not have motile spores. 4.0 True fungi (Kingdom Fungi or Eumycota) There are two major reasons for the incredible success the fungi enjoy. The first is the fungal spore, the second the fungal hypha. Spores permit rapid dispersal— fungal spores are (almost) everywhere. Some spores survive long periods, sometimes even years, of unfavorable conditions such as freezing, starvation, or desiccation. Diversity of spores among eumycotan fungi. 4.0 True fungi (Kingdom Fungi or Eumycota) Hyphae permit the thorough and intimate exploration and exploitation of newly available substrates. How many hyphal tips do you think there are in this illustration of a very young colony? The answer is 388, and this number will double every hour or so. Its strong, waterproof, chitinous hyphae; its richly branched growth pattern; the digestive enzymes it secretes at its growing tips—all these make it ideally suited for actively penetrating, exploring, and exploiting solid substrates. 4.1 Phylum Chytridiomycota The Chytridiomycetes, often referred to as chytrids, lack true mycelium. They have a round or irregularly shaped thallus, the walls of which contain chitin. They live entirely within the host cells. On maturity, the vegetative body is transformed into one or many thick-walled resting spores or sporangia. Chytridiomycetes are water- or soil-inhabiting fungi. Because they produce zoospores that have a single posterior flagellum, all require or are favored by free water or a film of water in the soil or on the plant surface. The class Chytridiomycetes contains three plant pathogenic genera: Olpidium, which infects the roots of many kinds of plants; Synchytrium, which causes black wart of potato; and Physoderma, which causes the crown wart of alfalfa [P. (formerly Urophlyctis) alfalfae] and the brown spot disease of corn (P. maydis). 4.1 Phylum Chytridiomycota The resting spores germinate to produce one or many zoospores, which infect plant cells and either produce thalli directly and cause the typical infection, or first produce zoosporangia. The zoosporangia produce secondary zoospores, which then cause the typical infection. Abundant moisture favors the local spread of the pathogens. Over long distances the pathogens are spread in infected plant parts or on contaminated plants and in soil. Infected plant cells are not usually killed. Instead, in diseases caused by Synchytrium and Physoderma alfalfae, cells in infected tissues are stimulated to divide and enlarge excessively. Olpidium can also transmit viruses from the hosts in which it is produced to those it infects next. It is a vector of at least six plant viruses, including tobacco necrosis virus and lettuce big vein virus. 4.1 Phylum Chytridiomycota Orders Chytridiales and Spizellomycetales are often parasitic, and their assimilative thallus often consists of a single cell. This cell is either (1) entirely converted into a reproductive sporangium (the holocarpic mode), as in Olpidium brassicae, or (2) differentiated into assimilative rhizoids and a sporangium (the eucarpic mode), as in Chytridium lagenaria or Spizellomyces punctatus. Other chytrids have a more extensive system of rhizoids, called a rhizomycelium, which may nourish several sporangia, as in Cladochytrium. We describe this multisporangial condition as polycentric to differentiate it from the monocentric forms just mentioned, which produce only a single sporangium. 4.1 Phylum Chytridiomycota Types of thalli and reproductive structures among the Chytridiomycota. A: eucarpic thallus of Spizellomyces punctatus (Spizellomycetales) in pine pollen; B: holocarpic thallus of Olpidium brassicae (Chytridiales) in a cell of cabbage root; C: polycentric thallus of Cladochytrium (Chytridiales); D: stages of oogamous reproduction in Monoblepharis polymorpha (Monoblepharidales). 4.1 Phylum Chytridiomycota (A) Black wart of potato caused by Synchytrium endobioticum. (B) Crown wart of alfalfa caused by Physoderma alfalfae. 4.2 Phylum Blastocladiomycota This phylum was previously an order within the Chytridiomycota. But in 2006, the order Blastocladiales was promoted to the rank of phylum by James et al. from molecular evidence. The thallus has both broad true hyphae and narrow rhizoids. Allomyces arbusculus, exhibits what we call a rotation between haploid and diploid thalli. Haploid thalli produce gametes in specialized gametangia, while diploid thalli produce flagellate zoospores and resting sporangia. In Allomyces, the gametes come in two sizes, which is a condition called anisogamy. The smaller, more mobile gamete(male) swims towards the larger, less mobile (female) gamete. Both kinds of gamete are formed on the same haploid thallus. The colorless female gametangia are located at the tips of hyphal branches, with the orange male gametangia immediately below. 4.2 Phylum Blastocladiomycota Zygotes develop into diploid thalli which bear two kinds of sporangia, thin walled and thick walled. The nuclei of thin-walled sporangia undergo repeated mitosis and produce mitospores, which in this case are diploid, uniflagellate zoospores that can establish new diploid thalli. The other kind of reproductive structures, resistant sporangia are thick walled, brown, and can survive for up to thirty years. Some environmental stimulus triggers reduction division (meiosis) in these sporangia, and the resultant haploid meiospores are liberated and develop into sexual thalli. 4.2 Phylum Blastocladiomycota Blastocladiales: life cycle of Allomyces arbusculus. 4.3 Phylum Neocallimastigomycota Some new and very different chytridiomycetous fungi living in the rumens of large herbivorous mammals were discovered in 1975. These fungi, mostly species of Neocallimastix, were obligately anaerobic. They differ from chytridiomycetes because they have no mitochondria and often had multi-flagellate zoospores. Fifteen species of anaerobic chytrids had been described by 1994. They produce rhizomycelia which efficiently penetrate plant material and have enzymes that more effectively break down cellulose than the cellulases of the mould Trichoderma. They are now classified as the order Callimastigales in phylum Neocallimastigomycota. 4.4 Phylum Zygomycota Zygomycetes have well-developed mycelia without cross walls. The name of the phylum is derived from the way in which its members reproduce sexually; by the fusion or conjugation of morphologically similar gametangia to form a zygosporangium (the teleomorphic phase). These usually develop thick walls and act as resting spores. Asexual or anamorphic phases of zygomycetes are easy to find on mouldy bread or peaches or on Anamorphs in the Zygomycota (Mucorales). horse dung and dog poop. 4.4 Phylum Zygomycota Zygosporangium development When compatible mycelia of Phycomyces blakesleeanus meet, they exchange chemical signals which establish that they are indeed sexually compatible. They loop back, swelling as they approach each other, and finally meet head on. After the walls between the two gametangial tips break down and their contents mix, it is isolated by two septa on either side and the nuclei fuse. This structure is now called a zygosporangium, and it develops a thick and often ornamented wall, even while still supported on either side by the former gametangia, which are now called suspensors Development of zygosporangium (teleomorph) in Phycomyces blakesleeanus (Mucorales). 4.4 Phylum Zygomycota Teleomorph and anamorph of Phycomyces. 4.4 Phylum Zygomycota Diseases caused by Zygomycetes They are either saprophytes or weak parasites of plants and plant products on which they cause soft rots or molds. When they infect living plant tissues, they first attack injured or dead plant parts. The fungi build up large masses of mycelium which secretes enzymes that diffuse into the living tissue and disrupt and kill the cells. Three genera of Zygomycetes are known to cause disease in plants or plant products: (1) Choanephora, which attacks the withering floral parts of many plants after fertilization and from there invades the fruit and causes a soft rot of primarily summer squash but also of pumpkin, pepper, and okra; and (2) Rhizopus and (3) Mucor, both common bread mold fungi, which in addition cause soft rot of many fleshy fruits, vegetables, flowers, bulbs, corms, and seeds. 4.4 Phylum Zygomycota Rhizopus rot of strawberries (A), of peach externally (B), and of peach in cross section (C). Sporangiophores with sporangia (D) and zygospore (E) of Rhizopus sp. 4.4 Phylum Zygomycota Control of soft rot caused by zygomycetes Avoid wounding fleshy fruits, roots, tubers, and bulbs during harvest, handling, and transportation. Discard or pack and store wounded organs separately from healthy ones. Clean and disinfect storage containers and warehouses with a copper sulfate solution, formaldehyde, sulfur fumes, or chloropicrin. Control temperatures of storage rooms and shipping cars. Pick succulent fruits, such as strawberries, in the morning when it is cool and keep them at temperatures below 10°C. Keep sweet potatoes and some other not so succulent organs at 25 to 30°C and 90% humidity for 10 to 14 days, during which the cut surfaces cork over and do not allow subsequent penetration by the fungus. Biological control of Rhizopus on stored peaches and nectarines has been achieved experimentally by treating them with yeasts of the genera Candida and Pichia. 4.5 Phylum Glomeromycota Composed of five orders, 29 genera, about 230 species of endomycorrhizal or arbuscular mycorrhizal fungi. They are involved in more mycorrhizal relationships (with plants) than any other group. Their hyphae enter the living root cells of perhaps 90% of all higher plants and establish with them obligate mutualistic symbioses called arbuscular mycorrhizas (AM) or endomycorrhizas. Their generally very large and thick-walled resting spores are common in most soils and are stimulated to germinate by the proximity of plant roots. 4.5 Phylum Glomeromycota Their usually nonseptate hyphae spread through the soil and enter living roots, where they develop diagnostic structures—intracellular, finely branched, tree-like arbuscules, which are the interface across which the fungus exchanges mineral nutrients, especially phosphorus, for photosynthates (sugars, etc.) provided by the plant. Many of the Glomeromycota produce both arbuscules and lipid-filled structures, called vesicles or intramatrical spores, inside plant roots. They are very efficient at mobilizing insoluble phosphorus and translocating it and other mineral nutrients to the plant. Since phosphorus is often the limiting nutrient for plant growth, AM fungi help plants to thrive in poor soils. These fungi are therefore vital in many natural habitats and of great potential value in agriculture.  4.5 Phylum Glomeromycota Diagrams of endo- and ectomycorrhizal structures. Finely branched arbuscule of an endomycorrhizal fungus inside a root cell of the photobiont. 4.6 Phylum Microsporidia These organisms (about 1,500 known species) are all intracellular parasites of animals, mainly insects but also fish, crustaceans, and even humans. They have no mitochondria or flagella and reproduce mostly by forming extremely resistant spores. Nosema is the best-known example and parasitizes many different insects. 4.7 Phylum Ascomycota Most have sexual stage (teleomorph) and asexual stage (anamorph) Ascospores (sexual spores), conidia (asexual spores) Ascus/ascocarp formation with 8 ascospores  4.7 Phylum Ascomycota I. Class Archiascomycetes — A group of diverse fungi, difficult to characterize Taphrina sp. Diseases caused: peach leaf curl, plum pocket, oak leaf blister, etc. The seed cavity tissues wither and Peach leaf curl die, forming a pocket Taphrina deformans within the fruit. Taphrina communis  4.7 Phylum Ascomycota II. Class Saccharomycetes – asci naked, no ascocarps produced - Mostly unicellular fungi that reproduce by budding Galactomyces sp. – causes citrus rot Saccharomyces cerevisiae – bread yeast, brewer’s yeast, baker’s yeast  4.7 Phylum Ascomycota III. Filamentous ascomycetes - Grouped according to shape of fruiting bodies  4.7 Phylum Ascomycota III. Filamentous ascomycetes Order Erysiphales (the powdery mildew fungi) —Asci in fruiting bodies completely closed (cleistothecia). - Mycelium, conidia, and cleistothecia on surface of host plant - Obligate parasites Blumeria sp. – cereals and grasses Erysiphe sp. – herbaceous plants  4.7 Phylum Ascomycota Leveillula sp. – tomato Oidium sp. (anamorph only) – tomato Uncinula necator – grapes  4.7 Phylum Ascomycota Groups according to fruiting body III.A. Pyrenomycetes: Ascomycetes with perithecia, or in some groups, cleistothecia - can either be in a stroma (“mattress”), immersed in a loose hyphal mat, or free Order Hypocreales Microascales Phyllachorales Ophiostomatales Diaporthales Xylariales  4.7 Phylum Ascomycota Order Hypocreales Hypocrea – anamorphs Trichoderma sp. and Gliocladium sp. used as biocontrol agents against several plant pathogenic fungi Trichoderma sp. Gliocladium sp. Melanospora – anamorphs Phialophora and Gonatobotrys parasitize the mycelium of pathogenic fungi like Ophiostoma, Ceratocystis, Fusarium, and Verticillium  4.7 Phylum Ascomycota Order Hypocreales Gibberella or Fusarium, causing foot or stalk rot of Claviceps, C. purpurea causing ergot of grain crops, corn and small grains which is poisonous to humans and animals  4.7 Phylum Ascomycota Order Hypocreales Endophytes – Epichloe, Balansia, Atkinsonella, and Myriogoenospora  4.7 Phylum Ascomycota Order Phyllachorales Glomerella sp. - anthracnose diseases; anamorphic stage is Colletotrichum gloeosporioides Phyllachora graminis – leaf spots on grasses  4.7 Phylum Ascomycota Order Ophiostomatales Ophiostoma novo-ulmi – Dutch elm disease Order Diaporthales Diaporthe – anamorph Phomopsis  4.7 Phylum Ascomycota III.B. Loculoascomycetes: Ascomycetes with ascostromata - Produce asci within locules (cavities) preformed in a stroma. Asci have a double wall. Order Dothideales Mycosphaerella sp.  4.7 Phylum Ascomycota Order Pleosporales Bipolaris – causes leaf spots and root rots on grain crops and grasses  4.7 Phylum Ascomycota Order Pleosporales Venturia – scab disease V. inaequalis (apple scab)  4.7 Phylum Ascomycota III.C. Discomycetes: Ascomycetes with apothecia - Ascocarps shaped like cups, saucers, or cushions are called apothecia. Monilinia – causing the brown rot disease of stone fruits  4.7 Phylum Ascomycota Sclerotinia – white mold or watery soft rot of vegetables S. sclerotiorum  4.7 Phylum Ascomycota III.D. Deuteromycetes or mitosporic fungi – imperfect or asexual fungi - Sexual reproduction and structures rare, lacking, or unknown - Asexual spores (conidia) formed on conidiophores existing singly, grouped in specialized structures such as sporodochia and synnemata, or produced in structures known as pycnidia and acervuli. Geotrichum candidum – sour rot of fruits and vegetables  4.7 Phylum Ascomycota Penicillium – blue mold rot of fruits Aspergillus – bread mold and seed decay 4.8 Phylum Basidiomycota Sexual spores, called basidiospores, are produced externally on a club-like, one- or four-celled spore producing structure called a basidium. Order Ustilaginales (the smut fungi) Ustilaginoidea virens Ustilago maydis 4.8 Phylum Basidiomycota Order Uredinales (the rust fungi) Puccinia P. graminis – small grains P. hordei – barley leaf rust P. coronata – crown rust of oats P. sorghi – corn rust P. polysora – southern corn rust P. purpurea – sorghum rust very specialized parasites attack only certain genera or certain varieties Rust fungi that are morphologically identical but attack different host genera are regarded as special forms (formae specialis) Puccinia graminis f. sp. tritici - wheat Puccinia graminis f. sp. hordei - barley 4.8 Phylum Basidiomycota Order Exobasidiales — basidiocarp lacking: basidia produced on surface of parasitized tissue bs – basidiospore m – mycelium 4.8 Phylum Basidiomycota Order Agaricales (the mushrooms) — basidium without cross walls, produced on radiating gills or lamellae. Many are mycorrhizal fungi. 4.8 Phylum Basidiomycota Common symptoms caused by Basidiomycetes.