1) a) Define Fungus. Enlist and Explain Characteristics of Fungi.
b) Define Plant Pathology. Explain Objectives & Importance of Plant Pathology.
Fungus are eukaryotic, spore bearing, achlorophyllous, heterotrophic organisms that generally reproduce sexually and asexually and whose filamentous, branched somatic structures are typically surrounded by cell walls containing chitin or cellulose or both with many organic molecules and exhibiting absorptive nutrition.
Characteristics of Fungi.
Somatic structures:
Thallus/ Soma Commonly called as vegetative body or fungal body. A thallus( pl. thalli) is a simple, entire body of the fungus devoid of chlorophyll with no differentiation into stem, roots and leaves lacking vascular system.
Hypha (hypha=web) ( pl. hyphae) : Hypha is a thin, transparent, tubular filament filled with protoplasm.It is the unit of a filamentous thallus and grows by apical elongation. Mycelium( pl. mycelia): A net work of hyphae ( aggregation of hyphae) constituting the filamentous thallus of a fungus. It may be colourless i.e., hyaline or coloured due to presence of pigments in cell wall.The mycelium may beectophytic or endophytic.
(Plant Pathology: It is a science that deals with the study of diseases of plants, their development and control is called plant Pathology or phyto pathology. (Phyton Plant, Pathos disease, logos = Science)
1. Impact of plant diseases on population:
The late blight of potato is a famous example in history of plant pathology, the disease assume epidemic proportion in Ireland in 1845 devastating the whole potato crop. The potato being the staple food of people & because of non availability of it, around 20 lakh people died due to starvation & migration of population to other lands including North American continent.
In India, Helminthosporium leaf spot of rice devaste rice crop in west Bengal in 1942-43 & thousands of people, died because of hunger & migrated to other part of country.
2. Change in Agricultural Pattern:
The diseases like coffee rust in Ceylon had changed the economy of country & shifting to other plantation crop like tea.
In 1885 their was epidemic of coffee rust in Ceylon which devasted the entire coffee rust went down from 228 kg/ acre to 101 kg/acre by 1878, &-because of which by 1893 the coffee export of Ceylon reduced by 93% thus making huge loss. The coffee rust became so Sevier that Ceylon has to shift itself to cultivation of tea.
3.Food Poisoning:
The poisoning of food due to plant disease is another evil. There is death of people & animal due to consumption of contaminated rye with ergot, which produces toxin fetal to human beings & animals. Also production of aflatoxin by Aspergillus flavus in foodstuff is also fetal to human beings.
4.Impact on Industry:
The certain agro industries are also affected due to supply of the diseased raw material for ex. The disease red rot of sugarcane affects the sugar industries because of poor recovery of sugar form such infested material which intern increases the cost of production.
5.Impact on science:
The plant disease system had provided a great scope for expanding the areas of human knowledge regarding, Micro-organism, their taxonomy, ecology, physiology & biochemistry, biophysios, genetic, molecular & cellular biology & managements practices for control of crop diseases.
6.Useful plant diseases:
The man has commercially exploited the plant disease for economic gain & aesthetic value for ex. Tulip breaking the disease of flower of tulip which cause variegation in flower of tulip are much prized & covered in west.
Objectives of Plant Pathology:
Plant Pathology (or) Phytopathology is one among the branches of Agricultural sciences that deals with cause, etiology, resulting the losses and management of plant diseases with following four major adjectives.
i. Study the disease (s)/ disorders caused by biotic and abiotic agents (s)
ii. Study the mechanism (s) of disease development by Plant Pathogens.
iii. Study the interaction between plant and pathogen in relation the overall environment.
iv. To develop suitable management strategies for managing the diseases and losses caused by them.
2) a) Enlist methods of Reproduction in Bacteria. Describe Characteristics of Bacteria.
b) Classify prokaryotes with one example of Genus according to Bergey’s Manual.
Classification of Phytopathogenic Prokaryotes,according to Bergey's manuak of systematic Bacteriology, 1984
KINGDOM: Prokaryotae
DIVISION I:Gracilicutes,Gram negative
CLASS: Proteobacteria,mostly single celled
FAMILY:Enterobacteriaceae
Eg.Erwinia
FAMILY:Pseudomonadacxeae
Eg:Pseudomonas, Xanthomonas, Rhizobacter
FAMILY:Rhizobiaceae
Eg.Agrobacterium
FAMILY UNKNOWN
Eg.Xylella
DIVISION II:Firmicutes, Geam positive
CLASS 1:Firmibacteria,mostly single celled
FAMILY:Bacillaceae
Eg.Bacillus
CLASS 2:Thallobacteria,branching bacteria FAMILY:Corynebacteriaceae
Eg Streptomyces, Clavibacter,Curtobacterium
DIVISION III; Tenericutes,no cell wall,only cell membrane
CLASS;Mollicutes
FAMILY:Spiroplasmataceae
Eg.Spiroplasma
FAMILY:STILL UNKNOWN
Known as Phytoplasmas
DIVISION IV:Mendesicutes
Eg.Primitive phylogenic Archaeobacteria
3) a) Define Reproduction. Enlist & Explain different Sexual & Asexual methods of reproduction in
fungi.
b) Enlist different Plant pathogenic organisms. Write Important characteristics of Viruses.
Reproduction in fungi:
Reproduction is the formation of new individuals having typical characters of the species. Fungi reproduce by spores. Spore is an unit of reproduction.
Asexual Reproduction in Fungi
It is also known as somatic or vegetative reproduction and does not involve the union of two nucleus/sex organs.
Methods of Asexual Reproduction:
1. By fragmentation of soma/cell sap/hyphae
2. Binary fission
3. Budding
4. Production of spores
1.By fragmentation of soma / cell sap/hyphae
Mycelium and each fragment grows into a new individual the hyphae break up into their component cells as oidia / arthrospores which behave like spores. If the cells become enveloped in a thick wall before they separate form other hyphal cell, adjoining them are called as chlamydospores e.g. Oidia of Powdery Mildew. Each fragment further germinate to form hyphae
2.Binary fission
Fission of somatic cell into daughter cells. parent cell divides into two by a formation of constriction or by formation of divider c.g. Yeast or True fungi
3. Budding
It is the production of bud/small outgrowth form a parent cell. A bud informed, the nucleus and parent cell divides and one daughter nucleus migrates into the bud. Bud increases in size and forms a new individual e.g. Rust and Smut fungi yeast fungi.
4. Production of spores
Spores produced may be conidia/sporangispores basipetal-oldest at the top and youngest at the bottom. Acropetal- oldest at the bottom and youngest at the top.
Sexual Reproduction in Fungi
Union of two nuclei or gametes of opposite sex a gamete is unisexual i.e. haploid
The process of sexual reproduction consists of three distinct phases.
1. Plasmogamy
Union of two protoplast bringing two haploid nuclei together in the same or common cell.
2. Karyogamy
Actual fusion of two haploid nuclei brought together as a result of plasmogamy. Karyogamy immediately follows plasmogamy.
3. Meiosis
The nuclear fusion is followed by meiosis (reducing division), meiosis reduces to number of chromosomes to haploid.
The sex organs in fungi are called gametanigia, Gametangia from differentiated sex cells called gametes or may contain one or more gamete nuclei.
Methods of sexual reproduction in Fungi
a. Planogametic copulation
b. Gametangial contact
c. Gametangial copulation
d. Spermatization
e. Somatogamy
f. Heterokaryosi
g. Dikaryotization
a. Planogametic copulation Fusion of two naked gametes, one/ both of which are motile. It is completed in three manners.
1. Isoplanogamtic copulation: It involves tow motile identical similar gametes
but differs in their physiology e.g. Synchytricum olpidium Isogamous: It male and female are of same shape and size.
2. Anisoplanogametic copulation: It involves union of dissimilar motile gametes of which one is larger than other, e.g. O-Blastocladiales Genus - Aliomyces
Anisogamous: Morphologically dissimilar but distinct is size and shape.
3. Heteroplanogametic copulation: Fusion of non-motile female gamete and motile male gamete is known as Heteroplanogametic copulation.
b. Gametangial contact.
In this method two gametangia of opposite sex comes in contact and one / more nuclei migrates form male to the female.
The male nuclei enters the female gametangium through a pore developed by the dissolution of gametangial walls at the point of contact while in other species fertilization tube acts as a passage for the male nuclei.
After the passage of nuclei has been accomplished the organisms continues its development in various ways and antheridium eventually disintegrates, e.g. Oomycetes Ascomycetes
c. Gametangial
Entire protoplast is transferred into the female gametangia a involves the fusion of two protoplast in a common cell. Sex gametes are indistinguishable/morphologica
identical. Copulation occurs either by complete fusion of tow protoplast. It is common in class- Trichomycetes and zygomycetes.
d. Spermatization
it involes the formation of small spores or seed like structures/ spermatia e.g. Spematiospores
Spermatia acts as a male gamete which is uninucleate/ spore like and carried out by wind, water, insects to the receptive hypha (female gametangium). A pore developed at the plant of contact and the contents of the spermatia passes into receptive hypha which serves as a female organ, e.g.Pycniospores and Receptive hypha is rusts.
c. Somatogamy
No gametes are involved. Vegetative hypha itself acts as male and female gamete and bring about sexual reproduction, e.g Smut fungi
f. Dikaryotization
Degenerate type of sexuality. It is accomplished through migration of nuclei form one cell to another cell of vegetative hypha, often through mechanism of clamps. The two nuclei remain in pair and divide as such and only fuse prior to the formation of spores. No special sex cells are produced. Clamp connections are formed during nuclear division, e.g. Class - Basidiomycetes
g. Heterokaryosis
It is defined as phenomenon of coexistence of genetically different nuclei in the cell and the individual which possess this condition is called as heterokaryotic. e.g. Fusarium, Alternaria.
This process is in the nature of vegetative grafting so commonly met within higher plants and is independent sex. It is 'brought about by hyphal fusion and anastomosis or bridging/vegetative hyphal /carrying nuclei of different genetically reactions and of common occurrence in Fungi Imperfecta, giving rise to new nuclear combination and resulting in the origin of new forms.
3) a) Define Reproduction. Enlist & Explain different Sexual & Asexual methods of reproduction in fungi.
Reproduction: Reproduction is the formation of new individuals having all the characteristics of the species. OR Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents".
Asexual methods of reproduction in Fungi:
i. Fragmentation
ii. Fission.
iii. Budding
iv. Sporulation ( production of spores)
Sexual methods of reproduction in Fungi :
i. Planogametic copulation.
ii. Gametangial contact
iii. Gametangial copulation
iv. Spermatisation
v. Somatogamy .
Flowering Plant Parasites: There are two types of parasites.
1) Root Parasites:
i) Striga (Partial root parasite):
ii) Orobanche (Complete root parasite)
2) Stem Parasites:
i) Dodder (Cuscuta) (Complete stem parasite)
ii) Loranthus (Partial Stem parasite)
1. Root Parasites:
1. Total or Complete or Holoparasite: Orobanche (Broom rape or Tokra)
It is annual flashy flowering plant growing to height of about 15-50 cm long, yellow or brownish colour and covered by small thin scaly leaves. Flowers appears in the axil of leaves are white or tubular. Fruits appears in the axil of leaves are white or tubular. Fruits are capsule containing and seeds are very small, black in colour remain viable for several years. The hausteria of parasite penetrates into the roots of hosts and draw its nourishment. The growth of the plant is retarded, may die some times. It attacks tobacco, tomato, brinjal, cabbage, cauliflower
b) Enlist different Plant pathogenic organisms. Write Important characteristics of Viruses.
List of Plant Pathogenic organisms -
- Fungi Bacteria,
- Viruses,
- Viroids,
- Phytoplasma,
- Fastidious vascular bacteria,
- Plant Pathogenic algae,
- Protozoa
- Nematodes
- Phanerogamic Plant parasites.
Virus:
1. They are Ultra microscopic in nature can be seed only under electron Microscope
2. Viruses are Nucleoproteineous in nature containing both Nucleic acid (either RNA or DNA) surrounded by Protein coat known as Capsid
3. The are Self-replicating
4. Viruses are Filterable in Nature can be easily pass through bacteria proof filter.
5. They are Acellular
6. The are Smaller than bacteria having size 20 to 300 nm (1nm=1/1000 mm)
7. The shapes of viruses are Rod to spherical, polyhedral
8. The complete mature single virus particle is called virion contain NA and protein
9. The viruses contain Nucleic Acid 5-40% and protein 60-95%
10. If Nucleic acid is RNA i.e., single or double stranded and if DNA it is mostly double stranded.
11. Smaller Protein subunit is called as capsomer.
12. Viruses are obligate parasite only depends on living host.
13. They are Intracellular parasite.
4) a) Write in detail causes of Plant Disease. Explain disease Triangle.
Disease triangle
• The interaction of the host, the pathogen and the environment results in disease development. It is generally illustrated by a triangle, also called a disease triangle. Disease Development in Plant Population
This is determined by:
• Host: All conditions in host that favour susceptibility.
• Pathogen: Total of virulence, abundance etc.
• Environment: Total of conditions that favour the pathogen and predispose the host plants to pathogen attack.
• Time: Specific point of time at which a particular event in disease development occurs and the duration or length of time during which the event takes place.
b) Explain Principles & Methods of Plant disease management.
i) Based on plant part affected
• Localized, if they affect only specific organs or parts of the plants.
• Systemic, if entire plant is affected. or
They can be classified as root diseases, stem diseases, foliage/foliar diseases, etc.
ii) Based on perpetuation and spread
• Soil borne -when the pathogen perpetuates through the agency of soil.
• Seed borne -when the pathogen perpetuates through seed (or any propagation material).
• Air borne -when they are disseminated by wind e.g. rusts and powdery mildews.
iii) Based on the signs and symptoms produced by the pathogens
• Diseases are classified as rusts, smuts, powdery mildews, downy mildews, root rots, wilts, blights, cankers, fruit rots, leaf spots, etc. In all these examples, the disease is named after the most conspicuous symptom of the disease appearing on the host surface.
iv) Based on the host plants affected
They can be classified as cereal crop diseases, forage crop diseases, flax diseases, millet diseases, plantation crop diseases, fruit crop diseases, vegetable crop diseases, flowering plant diseases, etc.
v) Based on major Causes
They can be classified as fungal diseases, bacterial diseases, viral diseases, mycoplasmal diseases, etc.
vi) Based on Infection Process
• Infectious -All the diseases caused by animate causes, viruses and viroids can be transmitted from infected host plants to the healthy plants and are called infectious.
• Non-infectious- Non-infectious diseases can not be transmitted to a healthy plant. Also referred as non-parasitic disorders or simply physiological disorders, and are incited by abiotic or inanimate causes like nutrient deficiency or excess or unfavorable weather conditions of soil and air or injurious mechanical influences.
vii) Classification of Animate Diseases in Relation to Their Occurrence
• Endemic diseases -which are more or less constantly present from year to year in a moderate to severe form in a particular geographical region, i.e. country, district or location.
• Epidemic or epiphytotic diseases - which occur widely but periodically particularly in a severe form. They might be occurring in the locality every year but assume severe form only on occasions due to the favourable environmental conditions occurring in some years.
• Sporadic diseases occur at irregular intervals and locations and in relatively few instances.
• Pandemic diseases: A disease may be endemic in one region and epidemic in another. When epiphytotics become prevalent through out a country, continent or the world, the disease may be termed as pandemic.
6) a) Classify the phanerogamic plant parasites with examples.
Flowering Plant Parasites:
There are two types of parasites.
1) Root Parasites:
i) Striga (Partial root parasite)
ii) Orobanche (Complete root parasite)
2) Stem Parasites:
i) Dodder (Cuscuta) (Complete stem parasite)
ii) Loranthus (Partial Stem parasite)
7) a) Define Fungicide. Classify Fungicides based on their chemical composition.
b) Write in brief different chemical formulations.
1. Emulsifiable concentrates (EC)
These are liquid formulations which can be diluted with water before application. The active ingredient is dissolved in a solvent. The fungicides and solvents will often not mix with water, so an emulsifying agent or water dispersible oil is mixed. When these emulsifiable concentrate is added to water, a milky mixture is formed, which is a suspension of active ingredient and emulsified solvent in the water. E.g, propiconazole, difenoconazole, etc.
2. Wettable powder (WP)
Wettable powder is a very common formulation for most of the fungicides, which is used for spray mixtures. The modern wettable powders are water-dispersible which have the quality to wet easily and disperse well in water. They are also called as Water-Dispersible Powders (WDP). The active ingredient is incorporated, usually at the rate of 30-80% with a finely ground inert dust (filler) such as kaolin, a wetting agent and a suspending emulsifying agent. E.g., Indofil M – 45, Blitox 50 WP, etc. A highly developed type of water-dispersible powder is called as colloidal powder, which is so finely divided that the individual particles will never sediment out. A typical colloidal powder contains 5-50% active ingredient with non-ionic wetting agents, thickening agents and a hydrophilic diluents (carrier).
3. Dusts (D)
Dust formulations usually contain 1-10% active ingredient for direct application in dry forms. They are manufactured in such a way that they are light enough to be carried by a slight breeze for a considerable distance. The finely divided particles of active ingredient are carried on a carrier particle. The commonly used carriers (diluents) are attapulgite, kaolin, talc, pyrophylite, diatomaceous earth, bentonite, calcium silicate, hydrated silica, calcium carbonate, magnesium carbonate, gypsum, lime, etc. E.g., Blimix 4 % dust, Micop D 06, etc.
4. Granules (Pellets)
Pellets are the formulations of the fungicide with inert material formed into particles about the size of coarse sugar. The granules normally contain 3-10% of the active ingredient. Due to their size, the granules do not drift but have limited application being confined to soil and seed treatments. Granules have the advantage they can be measured in dry form more easily and acurately than dusts or wettable powders. E.g., Topgun 50WG, Cosavit, Wokovit, Cumulas 80 WG, etc.
5. Suspension or slurries
A dry form of the active ingredient is mixed with a liquid in these formulations. Such formulations usually contain a high percentage of active ingredients similar to Wettable powders. They are mixed with water for final use and require agitation. These are mostly used as seed dressers in seed processing companies. E.g., Flovin 35 SC, Cumal L 27 SL, Share 40 SC.
6. Solutions
True solutions are formulations in which active ingredient or a combination of active ingredients and a solvent is dissolved in water. Solutions have the advantage of requiring no agitation after formulation is added in water. Now a day, the manufacturers are concentrating to develop new formulations to increase the efficacy of the chemicals. Some new formulations developed are soluble liquid (SL, e.g., Cumal L 27 SL and Casu – B 3 SL), Soluble powder (SP), Water-soluble concentrate (WSC), Suspension Concentrate (SC), e.g., Share 40 SC and Contaf plus 5 SC and Aqua Flow (AF).
8. b) Write in brief about Taxonomy, nomenclature & suffixes attached to various ranks
Taxonomy: The science of classification. It is concerned with principles of classification.
Classification: Grouping of organisms into classes, orders, families, genera, species etc.
Nomenclature: Art of naming living organisms. Binomial system of nomenclature was originally introduced by Carl Linnaeus for higher plants. Later, this classification was adopted to fungi by his students C. H. Persoon and E.M. Fries.
Some important rules of nomenclature:
1. According to International code of Botanical Nomenclature, the names of organisms should be binomial i.e., 2 parts. The first part is noun designating genus and the first letter of the genus name should be in capital. The second name is often an adjective, describing the noun which denotes the species, and the first letter should be in small letter. Eg. Puccinia graminis.
2. Binomials are usually derived from Greek or Latin.
3.Binomials when hand written should be underlined and when printed italicised.
4. Citation of author’s name: The full name or abbreviation name of scientist who described fungus first, follows the species name. Eg. Puccinia graminis Persoon or Pers.
5. Citation of two authors names: If name of species is transferred to another genus from original ( Botrytis infestans), the name of first author who first described species must be kept in parenthesis followed by name of second author who gave present status of species. i.e., Phytophthora infestans. Eg. Phytophthora infestans ( Mont.) de Bary.
6. The taxa (groups) used in classification are Kingdom, Division, Class, Order, Family, Genus and Species. Each category may be sub divided into sub groups like Sub- Division,Sub- Class, Sub- Order.
7. Species is the unit of classification or basic taxonomic category ( taxon).
8. Species sometimes broken into variety / formae speciales ( f.sp.) and varieties into races and races into biotypes.
Suffix attached to various ranks :
➢ Division ends with mycota
➢ Sub- Division ends with mycotina
➢ Class with mycetes
➢ Sub- class with mycetidae
➢ Order with ales
➢ Family with aceae
➢ No special ending for genus and species.
9) a) Explain Symptoms caused by Plant Nematodes.
b) Describe classification of Nematodes.
Most of the plant parasitic nematodes affect the root portion of plants except Anguina spp, Aphelenchus spp, Aphelenchoides spp, Ditylenchus spp, Rhadinaphelenchus cocophilus and Bursaphelenchus xylophilus. Nematode suck the sap of the plants with the help of stylet and causes leaf discolouration, stunted growth, reduced leaf size and fruits and lesions on roots, galls, reduced root system and finally wilting.
Symptoms of nematode disease can be classified as
A) Symptoms produced by above ground feeder nematodes
B) Symptoms produced by below ground feeder nematodes
A) Symptoms produced by above ground feeder nematodes
i) Dead or devitalized buds – Nematode infection kills growing buds
e.g. Aphelenchoides fragariae on strawberry.
ii) Crinkled stems and foliage - e.g. Wheat gall nematode, Anguina tritici
iii) Seed galls – e.g. Wheat gall nematode, Anguina tritici larva enter into the flower primordium and develops in to a gall.
iv) Necrosis & discolouration – e.g. Red ring disease of coconut, Rhadinaphelenchus cocophilus. Due to the infestation, red coloured circular area appears in the trunk of infested palm.
v) Leaf lesions - Symptom on broad-leafed foliage plants. e.g. Chrysanthemum foliar nematode, Aphelenchoides ritzemabosi
vi) Twisting of leaves and stem: e.g. In onion basal leaves become twisted when infested with Ditylenchus dipsaci.
vii) Leaf discolouration: The leaf tip become white in rice due to rice white tip nematode Aphelenchoides besseyi.
B) Symptoms produced by below ground feeder nematodes:
The nematode infest and feed on root portion and exhibit symptoms on below ground plant part as well as on the above ground plants parts and they are classified as I) Above ground symptoms II) Below ground symptoms
I) Above ground symptoms: -
i. Stunting: Reduced plant growth and the plant cannot able to withstand in adverse conditions. Patches of stunted plants appears in the field. e.g. Heterodera avenae – Molya disease in wheat & barley. Globodera rostochiensis – Golden nematode in potato
ii. Discolouration of foliage: Also due to nutritional deficiency e.g. Root lesion nematode, Pratylenchus coffeae,
iii. Wilting: e.g. Root-knot nematodes, Meloidogyne spp
iv. Decline and die back: eg. In banana decline and die back are caused by Radopholus similis.
II) Below ground symptoms:-
i. Root galling: e.g. Meloidogyne spp. – Characteristic galls on host roots Nacobbus spp
– Larger galls on beet & tomato.
ii) Reduced root system: Due to nematode feeding the root tip growth is arrested and the root produced branches. This may be of various kinds such as coarse root, stubby root and curly root.
a) Stubby roots – Stubby branches or rootlets arranged in cluster eg. Trichodorus christiei on corn
b) Coarse root – Lateral roots stopped growth with no branches e.g.
Belonolaimus longicaudatus on corn.
c) Curly root – The nematode retard the elongation of roots and cause curling of roots known as ‘Fish hook’ symptom. Eg. Injury caused by Xiphinema spp.
iii) Root lesions – Necrotic lesions e.g. Pratylenchus spp (soybean),
iv) Rotting – Nematode + Micro-organisms. e.g. Ditylenchus destructor – potato rot.
v) Excessive root branching – e.g. Meloidogyne hapla in tomato
10) a) Explain in short Classification of Plant diseases.
i) Based on plant part affected
• Localized, if they affect only specific organs or parts of the plants.
• Systemic, if entire plant is affected. or
They can be classified as root diseases, stem diseases, foliage/foliar diseases, etc.
ii) Based on perpetuation and spread
• Soil borne -when the pathogen perpetuates through the agency of soil.
• Seed borne -when the pathogen perpetuates through seed (or any propagation material).
• Air borne -when they are disseminated by wind e.g. rusts and powdery mildews.
iii) Based on the signs and symptoms produced by the pathogens
• Diseases are classified as rusts, smuts, powdery mildews, downy
mildews, root rots, wilts, blights, cankers, fruit rots, leaf spots, etc. In all these examples, the disease is named after the most conspicuous symptom of the disease appearing on the host surface.
iv) Based on the host plants affected
They can be classified as cereal crop diseases, forage crop diseases, flax diseases, millet diseases, plantation crop diseases, fruit crop diseases, vegetable crop diseases, flowering plant diseases, etc.
v) Based on major Causes
They can be classified as fungal diseases, bacterial diseases, viral diseases, mycoplasmal diseases, etc.
vi) Based on Infection Process
• Infectious -All the diseases caused by animate causes, viruses and
viroids can be transmitted from infected host plants to the healthy plants and are called infectious.
• Non-infectious- Non-infectious diseases can not be transmitted to a healthy plant. Also referred as non-parasitic disorders or simply physiological disorders, and are incited by abiotic or inanimate causes like nutrient deficiency or excess or unfavorable weather conditions of soil and air or injurious mechanical influences.
vii) Classification of Animate Diseases in Relation to Their Occurrence
• Endemic diseases -which are more or less constantly present from year to year in a moderate to severe form in a particular geographical region, i.e. country, district or location.
• Epidemic or epiphytotic diseases - which occur widely but periodically particularly in a severe form. They might be occurring in the locality every year but assume severe form only on occasions due to the favourable environmental conditions occurring in some years.
• Sporadic diseases occur at irregular intervals and locations and in relatively few instances.
• Pandemic diseases: A disease may be endemic in one region and epidemic in another. When epiphytotics become prevalent through out a country, continent or the world, the disease may be termed as pandemic
b) Describe in details the Concept of Plant Disease.
Disease triangle
• The interaction of the host, the pathogen and the environment results in disease development. It is generally illustrated by a triangle, also called a disease triangle.
Disease Development in Plant Population
This is determined by:
• Host: All conditions in host that favour susceptibility.
• Pathogen: Total of virulence, abundance etc.
• Environment: Total of conditions that favour the pathogen and predispose the host plants to pathogen attack.
• Time: Specific point of time at which a particular event in disease development occurs and the duration or length of time during which the event takes place.
11. b) Explain the sexual spore fruits in fungi with suitable example.
Sexual Spore Fruits:
Ascocarps:
It is the spore fruit produced by the fungi belonging to the phylum
Ascomycota. Sexual spore produced endogenously are known as ascospores in sac like structure called ascus (Pl -Asci). The spore fruits are of various forms and shaped viz., spherical, flask, cup, saucer, pod, etc.
Following are the different types of ascocarps:
1. Cleistothecium (Pl. cleistothecium):
It is closed without ostiole, round to oval ascocarp with irregularly arranged or scattered asci having dark brown to black colour and provided with appendages to anchor or to hold host and to help in dissemination. Cleistothecium breaks open at maturity by wear and tear, e.g. powdery mildew fungi of order Erysiphales.
2. Perithecium (Pl. Perithecia):
A flask shaped ascocarp with narrow neck like ostiole through which asci are released. The sterile structures present in between the asci within the ascocarp are known as paraphyses, which help asci in nutrition and dispersal, e.g. Claviceps, Glomerella, etc.
3. Apothecium (Pl. Apothecia):
A cup or saucer shaped spore fruit with broad opening is known as apothecium. The asci are arranged in palisade layer called hymenium. The apothecium is usually fleshy and leathery in nature, e.g. genus Sclerotinia.
4. Ascostroma:
The asci are formed directly in a locule or cavity within at stroma. The stroma forms the wall of the ascocarp.
