FUNGI
Fungus is a Latin word , which means mushroom . Fungi are achlorophyllous (but carotenoids are normally present ) , heterotrophic thallophytes . Study of mashrooms or study of fungi is called mycology .
Term fungus was used by a group name by Gaspard Bauhin . Father of mycology is Pier Antonio Micheli . He wrote Nova Genera Plantarum . Father of Modern Mycology and Plant pathology is de Bary . Father of Indian Mycology and plant pathology is E. J. Butler . Largest fungus is Bracket fungi and smallest fungus is Yeast . The largest organism is a fungus Amillaria ostoyae spread in area of thousands of acres . Puffball is a fungus . Luminescent fungi parts are pileus in Panus and Pleuronus species .
General characteristics of fungi
1. Plant body is made up of branched filamentous hyphae . Hyphae form mycelium . Mycelium is absent in yeast , Synchytrium .
2. Hyphae are aseptate ( cystopus ) and coenocytic ( in phycomycetes ) or septate ( in ascomycetes , basidiomycetes , deuteromycetes ) .
3. Septa have simple pores . But in basidiomycetes , septa have dolipores . On both sides of dolipore , double membraned cap or parenthosome occurs .
4. Main component of cell wall is chitin ( fungal cellulose ) .
5. Motile cells are absent in the life cycle of higher fungi ( ascomycetes , basidiomycetes , deuteromycetes ) .
6. Modification of fungal mycelium -
Prosenchyma - Hyphae are loosely interwoven , more or less parallel to one another .
Pseudo-parenchyma - closely interwined, running in all directions , hyphae are not distinguishable , resemble parenchyma .
Rhizomorph - a thick strand of underground hyphae resembling a root
Sclerotium - compact globose structure , survive for long periods .
Haustorium - intracellular absorbing structures in obligate parasitic fungi , absent in Synchytrium .
Appressorium - terminal swollen strucutre of infectious hyphae of parasitic fungus .
Stromata - compact structure like mattresses
Hyphal traps - network of hyphal loops , help in capturing nematodes .
7. Fungi may be eucarpic ( only a part of vegetative mycelium frorms reproductive unit ) eg .yeast ,or holocarpic ( whole vegetative cell is transformed into a reproductive unit ) e.g. synchytrium .
8. All fungi are heterotrophs . Some are obligate parasites like Albugo , Puccinia . Synchytrium is an intracellluar parasite .
9. Ascospors ( endogenous origin ) and basidiospores ( exogenous origin ) are sexually produced spores .
10 . Asexual spores are zoospores , chlamydospores , aplanspores , oidia etc .
Sexual reproduction in fungi
There is progressive complexity in vegetative body and a gradual degeneration of sex organs in fungi . Sexual reproduction in fungi involves plasmogamy , karyogamy and meiosis . It takes place by -
1. Planogametic coupulation - It is fusion of two naked motile gametes . It is of 3 types -
a. Isogamy ( morphologically similar but physiologically different gametes ) - Synchytrium
b. Anisogamy ( both morhologically & physiologically idfferent ) - Allomyces
c. Oogamy (motile male gamete & non-motile female gamete ) - It is of 3 types
i. Gametangial contact ( involves fertilization tube ) - Albugo , Aspergillus , Pythium , Phytophthora
ii. Gametangial coupulation - Mucor , Rhizopus
iii. Spermatization ( sex organs absent , spermatia & receptive hyphae ) - Puccinia
iv. Somatogamy ( fusion of two vegetative cells ) - Peziza , Agaricus .
Taxonomic status of fungi
Ainsworth treated fungi as separate kingdom Mycota . Alexopoulus and Mims also included fungi in separate kingdom Myceteae . The classification of fungi is not yet settled . Gwynne-Vaugham and Barnes , Gaumann and Dodge , Tippo , Bessey , Martin , Alexopoulus , Alexopoulus and Mims , Ainsworth etc proposed the classification of fungi . Criteria for classification were thallus organisation , kinds of asexual spores , presence or absence of sexual reproductin , nature of life cycle etc . According to latest classification of Ainworth , Fungi includes -
Kingdom Mycota - It includes 2 divisions .
Division 1 Myxomycota ( slime molds ) - It includes 4 classes .
1. Acrasiomycetes
2. Hydromyxomycetes
3. Myxomycetes
4. Plasmodiophoromycetes
Division 2 Eumycota ( true fungi ) - It includes 5 sub divisions .
Sub division Mastigomycotina -
1. Chytridiomycetes
2. Hypochytridiomycetes
3. Oomycetes
Sub division zygomycotina
1. Zygomycetes ( sometimes called phycomycetes )
2. Trichomycetes
Sub division ascomycotina
1. Hemiascomycetes
2. Loculoascomycetes
3. Plectomycetes
4. Laboulbeniomycetes
5. Pyrenomycetes
6. Discomycetes
Sub division Basidiomycotina
1. Teliomycetes
2. Hymenomycetes
3. Gasteromycetes
Sub division Deuteromycotina
1. Blastomycetes
2. Hyphomycetes
3. Coelomycetes
Heterothallism in fungi
Heterothallism is a condition where two complementary mating types are needed for sexual reproduction . It was discovered by A. F. Blackeslee in mucorales .
It may be of 2 types -
1. Morphological heterothallism - Two mating types are morphologically different . It is also called haplodioecious . Example - Achlya ambisexualis .
2. Physiological heterothallism - Two mating types are morphologically similar but physiologically different . It is also known as haploid incompatibility . It is of 2 types -
A. Two allele heterothallism - Sexual compatibility is governed by a single pair of genetic factors ( A , a ) . Example Mucor mucedo .
B. Multiple allele heterothallism - Sexual compatibility is governed by more than two alleles . It may be of two types -
( a ) Bipolar - Bipolar multiple allele heterothallism is governed by more than two alleles of a single locus ( L1 , L2 , L3 ..... where L1 is compatible two any other allele except L1 ) . It is characteristic feature of basidiomycetes except rusts and smuts .
( b ) Tetrapolar - Tetrapolar multiple allele heterothallism is governed by more than two alleles of two locus ( A1B1 is not compatible to A1B1 , not fully compatible to A1B2 , A2B1 etc but compatible to A2B2 . Example Ustilago maydis .
Homothallic fungi - They have single mating types . They may be primary ( have uninucleate spores ) or secondary ( have binucleate spores with two compatible nuclei ) .
Parasexuality
It was discovered by Pontecorvo and Raper in Aspergillus nidulans . It is common in fungi in which sexual process is absent ( deuteromycetes ) though it also occurs in several fungi with sexual reproduction . Parasexuality is a process in which plasmogamy , karyogamy and meiosis do take place , but not at specific time or specific points in the life cycle of fungus . Meiosis in sexual cycle and mitosis in parasexual cycle are responsible for genetic recombination ( most imp difference ) .
The sequence of steps in this process are -
1. Formation of hetrokaryotic mycelium is the first important & necessary step . Most common method for this is anastomosis ( fusion of two hyphae ) .
2. It results in the formation of heterozygous diploid nucleus ( A and B , AA , BB , AB ) .
3. Mutiplication of this diploid nucleus ( 1: 1000 in comparision of multiplication of haploid nucleus ) .
4. Occasional mitotic crossing over during multiplication of diploid nucleus results in new gene recombinations . It is most important step .
5. These new recombinations of diploid nuclei are sorted out as diploid conidia . These diploid conidia germinate in diploid mycelia .
6. Occasionally some hypha of diploid mycelium form haploid conidia ( haploidization ) .
7. These haploid conidia are sorted out as haploid mycelia .
Parasexuality can be used in developing mycelium strains of desirable characters , in analysis of genetic and physiological processes of perfect and imperfect fungi .
Sex hormones in fungi
Some important sex hormones in fungi ( Allomyces , Achlya , Mucor mucedo etc ) are sirenin , antherdiol and oogoniol , hormone-D , trisporic acid , yeast alpha factors etc .
Economic importance of fungi
Benificial importance
1. Sufu is obtained from Mucor and Antimucor species .
2. Basidiocarps of Agaricus campestris , Morchella esculenta ( guchhi ) are edible fungus .
3. Ergot ( powerful hallucinogenic drug ) is obtained from the sclerotia of Claviceps purpurea .
4. Penicillin , wonder drug was for the first time extracted from sac fungi Penicillium notatum by Alexander Fleming in 1944 . At large scale it is obtained from P. chrysogenum . Griseofulvin is obtained from Penicillium greseofulvum . Fumagillin is obtained from Aspergillus fumigatus . Clavicin is obtained from Aspergillus clavatum . Ergotin is obtained from Claviceps purpurea . Cephalosporin is obtained from Cephalosporium .
5. Yeast cells are best source of vitamin B .
6. Organic acids - Citric acid is produced by fermentation of sugar by Aspergillus niger .
7. In research , Physarum polycephalum is very good study material for DNA synthesis , morphogenesis and mitotic cycle . Neurospora is referred as Drosophila of plant kingdom .
8. In brewery , Saccharomyces cerevisiae is used in the production of alcohol from sugar (glucose) , beer . P. camembertile , P. rocqueforti are used in cheese industry .
9. Enzyme invertase and zymase is produced by Saccharomyces cerevisae . Amylase is obtained from Aspergillus niger .
10. In agriculture ,Trichoderma is used in biological control of diseases .
11. Species like Rhizoctonia , Phoma etc show symbiotic relationship with roots of higher plants . This is called mycorrhiza .
12. Gibberellin is otained from Gibberella fujikuroi .
Harmful importance
1. Aflatoxin , a powerful toxin is produced by Aspergillus .
2. Amanita phlloides is a poisonous fungus .
3. Plant diseases - Early blight of potato -Alternaria solani
Irish famine ( Late blight of potato) - Alternaria solani
Red rot of sugarcane - Colletotrichum fulcatum
Downy mildew of pea - Peronospona pisi
Bengal famine ( brown leaf spot of rice ) - Helminthosporium oryzae
Salmon disease of fishes - Saprolegnia
Panama disease of banana - Fusarium oxysporum
Ergot of rye - Claviceps purpurea
Powdery mildew - Erysiphens
Black wart disease - Sychytrium endobioticum
White rust of crucifer - Albugo candida
Loose smut of barley - Ustilago nuda
Loose smut of wheat - Ustilago tritici
Black rust of wheat - Puccinia graminis tritici
Tikka disease of groundnut - Cercospora personata
Wilt of arhar - Fusarium udum
4. Animal diseases -
Athelete foot - Tinea rubrum
Mucomycosis - Mucor , Rhizopus
Aspergillosis - Asppergillus flavus , A. niger
Bordeaux mixture
It is mixture of copper sulphate and lime . It is used common antifungal . It was prepared by Millardet .