2020 Solved Old Paper (BOT - 201) New

Ans.
Puffballs are distinguished from other mushroom groups by the fact that they lack many of the features or characteristics that other common mushrooms possess. A puffball has no stem. It has no cap. And no external gills.

Ans.
Parasexual Cycle:-
> Until 1944, the sexual cycle was the only means of exchange of genetic material.
> It is to the credit of microbial geneticists that a series of novel methods of genetic recombination are now known in bacteria, which do not involve karyogamy and meiosis.
> These are transformation, conjugation, transduction, lysogeny, and sexduction which differ from the standard sexual cycle.
> A similar alternative to sexual reproduction was discovered in the imperfect fungus, Aspergillus nidulans, in 1952 by Pontecorvo and Roper Glasgow. They called this parasexual cycle.
> In this, genetic recombination occurs in somatic cells by the mechanism of mitotic crossing over, which brings the same result as is achieved by the meiotic crossing over.
> The parasexual cycle involves the following steps:
i. Formation of heterokaryotic mycelium
ii. Nuclear fusions and multiplication of the diploid nuclei
iii. Mitotic crossing over during division of the diploid cells
iv. Sorting out of the diploid strains
v. Haplodization

Ans.
1. Fungal disease symptoms:-
> Birds-eye spot on berries (anthracnose)
> Damping off of seedlings (phytophthora)
> Leaf spot (septoria brown spot)
> Chlorosis (yellowing of leaves)
2. Bacterial disease symptoms:-
> Leaf spot with yellow halo
> Fruit spot
> Canker
> Crown gall
> Sheperd’s crook stem ends on woody plants
3. Viral disease symptoms:-
> Mosaic leaf pattern
> Crinkled leaves
> Yellowed leaves
> Plant stunting

Ans.
Incubation:- The incubation period is the time interval from when a person is initially exposed to a pathogen to when the symptoms of the infection first manifest. The term incubation period is usually reserved and used by epidemiologists to discuss infectious diseases, particularly those caused by viruses.
Infection:-
The infectious period is the time interval when a person can first transmit an infection to other people to when they are no longer contagious. An illness in which there is a longer infectious period is more likely to persist for longer in a population as there are more chances for contagion and spread. 

Ans.
Features:-
> Mostly they are terrestrial, parasitic or coprophilous.
> They are unicellular or multicellular fungi.
> The mycelium is made up of septate and branched hyphae.
> The cell wall is made up of chitin or β-glucans.
> There is cytoplasmic continuity due to septal pores.
> Asexual reproduction is by the formation of conidia exogenously on conidiophores.
> Yeast reproduces asexually by budding.
> Sexual reproduction is by conjugation between two gametangia. They are either homothallic or heterothallic.
> The fruiting body is known as ascocarp. There are four types of ascocarps:
i. Cleistothecium:- The fruiting body is spherical and remains tightly closed, e.g. Aspergillus
ii. Perithecium:- The fruiting body is flask-shaped with one external opening, e.g. Neurospora
iii. Apothecium:- The fruiting body is cup-shaped and asci are present in hymenium, e.g. Peziza
iv. Ascostroma:- There is no differentiated fruiting body. Asci are present in the stroma, e.g. Mycosphaerella
> Ascospores are produced endogenously in asci.
Sexual Reproduction in Ascomycetes:-
> Two different mating types hyphae come together and fuse.
> Plasmogamy takes place, but it does not follow karyogamy immediately.
> The fused structure contains two haploid nuclei from each parent, i.e. dikaryon.
> New hyphae are produced with dikaryotic cells.
> At the tip of the hyphae, asci develop in the ascocarp.
> In each ascus, two nuclei fuse together (karyogamy) to form a diploid zygote.
> Formation of Ascospores: The diploid zygote undergoes meiosis to form 4 haploid nuclei, which undergo mitotic division to form 8 haploid nuclei. Each of the nuclei accumulates cytoplasm and a thick cell wall surrounds it. These are known as ascospores.
> Ascospores are released from asci through pore, slit or hinged lid and dispersed by air currents. Under favourable conditions, ascospores germinate to form new mycelia.

Ans.
Environmental conditions influence plant diseases:- Plant diseases are ubiquitous throughout the world wherever plants grow, but of more common occurrence in humid to wet area with cool, warm or tropical temperatures. Diseases most commonly occur during wet, warm days and night and on plants heavily fertilized with nitrogenous fertilizers. So, environmental conditions frequently determine whether a particular disease will occur or not. Most common environmental factors that have considerable influence on development of plant disease are temperature and moisture. Other factors include wind, light, soil pH, soil structure etc.
1. Effect of temperature:-
> Each pathogen has an optimum temperature for its growth.
> Different growth stages of fungus, such as the production of spores, their germination and the growth of the mycelium may have slightly different optimum temperature.
> Storage temperatures for certain fruits, vegetables and nursery stock are manipulated to control fungi and bacteria that causes storage decay, provided the temperature does not change quality of products.
> In temperate regions, low temperature during late fall, winter or early spring are not congenial for the development of pathogen, but as the temperature rises, these pathogens become active and when other conditions are favourable they can cause infection and thus disease.
> Pathogen differs in their preference for higher or lower temperature. For example, the fungi namely Typhula and Fusarium causing snow mould of cereals and turf grasses, late blight pathogen > Phytophthora infestans are more serious in cold regions whereas fungus like Colletotrichum, Ralstonia are favoured by higher temperature.
> Rapid disease development occurs when temperature is optimum for pathogen development and is below or above the optimum for host development.
> For stem rust of wheat (Puccinia graminis tritici) completion of infection cycle is 22 days at 5°C, 15 days at 10°C and 5-6 days at 23°C.
> The minimum, optimum and maximum temperature for the pathogen, host and disease are same, the effect of temperatures in disease development is apparently through its influence on pathogen.
> Effects of temperature may mask symptoms of certain viral and mycoplasmal diseases and making them more difficult to detect.
2. Effect of moisture:-
> Moisture influences the initiation and development of infectious plant diseases in many interrelated ways.
> It may exist as rain or irrigation water on plant surface or around the roots, as relative humidity in the air and as dew.
> Moisture is indispensable for the germination of fungal spores and penetration of the host by germ tube.
> It is also indispensable for the activation of bacterial, fungal and nematode pathogens before they can infect the plant.
> Moisture in the form of splashing rain and running water also plats an important role in the distribution and spread of many of the pathogens on the same plant and on other plants.
> Moisture also increases the succulence of host plants and thus their susceptibility to certain pathogens, which affects the extent and severity of disease.
3. Effect of rainfall:-
> The occurrence of many diseases in a particular region is closely correlated with the amount and distribution of rainfall within year.
> Late blight of potato, apple scab, downy mildew of grapes and fire blight are found or are severe only in areas with high rainfall or high relative humidity during the growing season.
> In apple scab, continuous wetting of the leaves, fruits etc. for at least 9 hours is required for primary infection to take place even at optimum range (18 to 23°C) of temperature.
> At lower temperature the minimum wetting period required is higher.
> In powdery mildews, spore germination and infection are actually lower in the presence of free moisture on the plant surface than they are in its absence.
4. Effect of Relative humidity:-
> Relative humidity is very critical in fungal spore germination and the development of storage rots.
> Rhizopus soft rot of sweet potato (Rhizopus stolonifer) is an example of storage disease that does not develop if relative humidity is maintained at 85-90 %, even if the storage temperature is optimum for the growth of the pathogen. Under these conditions, the sweet potato root produces corky tissues that wall off the Rhizopus fungus.
> Moisture is generally needed for fungal spore germination, the multiplication and penetration of bacteria and the initiation of infection e.g., germination of powdery mildew spores occurs at 90-95 % relative humidity.
5. Effect of soil moisture:-
> Soil moisture influences the initiation and development of infectious plant diseases.
> High or low soil moisture may be a limiting factor in the development of certain root rot diseases.
> High soil moisture levels favours development of destructive water mould fungi, such as species of Aphanomyces, Pythium and Phytophthora.
> Overwintering by decreasing oxygen and raising carbon-dioxide levels in the soil makes roots more susceptible to root rotting organisms.
> Diseases such as take all of cereals (Gaeumannomyces graminis), charcoal rot of corn, sorghum and soyabean (Macrophomina phaseolina), common scab of potato (Streptomyces scabies) and onion white rot (Sclerotium cepivorum) are most severe under low moisture levels.
6. Effect of wind:-
> Most plant diseases that occurs in epidemic portions and spread in large areas are caused by fungi, bacteria and viruses that are spread either directly by wind or indirectly by insects which can travel long distances with the wind.
> Uredospores and many conidia are transported to many kilometers by wind.
> Wind becomes more important when it is accompanied by rain.
> Wind blown rain splashes can help in spread of bacteria from the infected tissues.
7. Effect of light:-
> Light intensity and duration may either increase or decrease the susceptibility of plants to infection and also the severity of disease.
> Light mainly cause production of etiolated plants due to reduced light intensity which in turn increases the susceptibility of plants to non-obligate parasites but decreases the susceptibility of plants to obligate parasites.
> It also enhances the plants’ susceptibility to viral infections.
8. Effect of soil pH:-
> Soil pH is a measure of acidity or alkalinity and it markedly influences occurrence of soil borne pathogens.
> Growth of potato scab (Streptomyces scabies) pathogen is suppressed at a pH of 5.2 or slightly below but is more severe at a pH 5.2 to 8.0 or above.
> Club root of crucifers caused by Plasmodiophora brassicae is most severe at a pH of 5.7, whereas its development drops sharply between 5.7 and 6.2 and is completely checked at pH 7.8.
9. Effect of soil type:-
> Certain pathogens are favored by loam soils and others by clay soils.
> Fusarium wilt disease which attacks a wide range of cultivated plants causes more damage in lighter and higher soils.
> Nematodes are also most damaging in lighter soils that warm up quickly.
10. Effect of host-plant nutrition:-
> Nutrition affects the rate of growth and the state of readiness of plants to defend them against pathogenic attack.
> Nitrogen abundance results in the production of young, succulent growth, a prolonged vegetative period and delayed maturity of the plants.
> These effects make the plant more susceptible to pathogens that normally attack such tissues and for longer periods.
> In contrast, plants suffering from a lack of nitrogen are weaker, slow growing and faster aging.
> Such plants are susceptible to pathogens that are best able to attack weak, slow-growing plants.
> Large amounts of nitrogen increases the susceptibility of pear to fire blight (Erwinia amylovora), wheat rust (Puccinia) and powdery mildew (Erysiphe).
> Reduced availability of nitrogen may increase the susceptibility of tomato to Fusarium wilt and Alternaria solani, of sugar-beets to Sclerotium rolfsii and of most seedlings to Pythium damping-off.
> Severity of the disease caused by Fusarium spp., Plasmodiophora brassicae and Sclerotium rolfsii increases when an ammonium fertilizer is applied whereas the severity of diseases caused by Streptomyces scabies and Gaeumannomyces graminis increase when nitrate form of fertilizers are applied.
> Phosphorus has been shown to reduce the severity of potato scab but to increase the severity of cucumber mosaic virus on spinach and Septoria infection of wheat leaves and glumes.
> Phosphorus seems to increase resistance either by improving the balance of nutrients in the plant or by accelerating the maturity of the crop and allowing it to escape infection by pathogens that prefer younger tissues.
> Potassium has also been shown to reduce the severity of numerous diseases including stem rust of wheat and early blight of tomato, whereas high amounts of potassium increase the severity of rice blast and root knot.
> Potassium seems to have a direct effect on the various stages of pathogen establishment and development in the host and an indirect effect on infection by promoting wound healing.
> Calcium reduces the severity of several diseases caused by root and stem pathogens such as Rhizoctonia, Sclerotium, Botrytis and Fusarium oxysporum, but it increases the severity of common scab of potato (Streptomyces scabies).
> The effect of calcium on disease resistance seems to result from its effect on the composition of cell walls and their resistance to penetration by pathogens.
> In general, plants receiving a balanced nutrition, in which all required elements are supplied in appropriate amounts, are more capable of protecting them from new infections and of limiting existing infections than plants to which one or more nutrients are supplied in excessive or deficient amounts.
11. Effect of pollutants:-
> Air pollutants cause various types of direct symptoms on plants exposed to their high levels.
> Ozone may affect a pathogen and sometimes the disease it causes. For example in wheat rust fungus, ozone reduces the growth of uredia and of hyphal growth and also the number of uredospores produced on ozone injured leaves.
> Ozone increases the infection of potato leaves by Botrytis.

Ans.
Asexual Spores:- Fungi reproduce asexually by mitospores. There are 2 types of mitospores based upon origin -
a. Endogenous spores:- These spores are produced inside a sac like structure sporangium. These spores are also called as sporangiospores. Eg. - Lower Fungi
They are of 2 types based upon motility:-
b. Exogenous spores:- These spores are borne externally and remain in contact directly to the externam environment. These spores are also called as conidia. Conidia are always produced in basipetal order. Eg.- Higher Fungi
Sexual Spores:-
Development of ascus:- It is developed from apical cell of ascogenous hypha. It is of 2 types -
i. Direct development (Free cell formation development):- 
ii Indirect development (Crozier formation development):- 
Development of basidium:- It is developed from apical cell of hypha of secondary mycelium.

Ans.
Plant Disease control by Physical methods:-
> The hot water treatment method of Jensen was developed in 1887 which was used to control loose smut disease of wheat, barley and Oats. Until the development of systemic fungicide hot water treatment was the only method to control loose smut. Hot water treatment is also effective in the control of nematodes.
> Solar energy treatment to control loose smut was first developed by Lutlzra. In this method seeds are first rinsed or soaked in water for 4-5 hrs. before drying them in scorching sun.
> Hot air treatment for the control of virus in propagating stocks was first developed by Kunkal in Peach yellow.

Plant Disease control by Chemical methods:-
> Chemical barrier to protect the host plant and/or eradicate an existing infection.
> Pesticides typically cannot “cure” heavily diseased plants.
> Types of pesticides:- fungicides, bactericides, nematicides, insecticides, biocides.
> Contact fungicide:- effective only at the site of application (protectant) must be applied before pathogen infects the plant; new growth emerging after application is not protected. examples: mancozeb, coppers, chlorothalonil, captan.
> Systemic fungicide:- absorbed & translocated (moved from application site) by the plant locally systemic = moves short distances (towards leaf margin) within the plant from the site of application (e.g., benomyl, triforine) systemic = moves further within the plant from the site of application (e.g., metalaxyl moves from roots up to shoots and foliage).
Methods:-
a. Seed treatment:- With fungicide before transplanting.
i. Soil treating chemicals:- It is used for controlling such soil borne diseases which attack on seeds or seedlings. The examples of such chemicals are – Formaldehyde, Captan, Thiram, Zineb, Organo-mercurials, PCNB, Ethylene dibromide, vapam etc.
ii. For Externally seed borne diseases, chemicals such as formalin, copper carbonate, captan, organo-mercurials (Agrosan GN and Ceresan) are used for seed treatment.
iii. For Internally seed borne diseases (i.e. loose smut), hot water treatment and solar treatment are used.
iv. Systemic Organic Compounds are effective chemicals for controlling both externally and internally seed borne diseases eg. Oxanthin derivatives (Plantvax and Vitavax), Benlate, Bavistin, Demosan.
v. For controlling air borne diseases, foliar application of chemicals is more effective.
vi. The common copper fungicides are: Perenox, Perelan, Blitox, Cuprokyt, Cuprosanand Fytolan. Its use is comparatively better than that of Bordeaux mixture.
b. Seed dressing:- With organomercurials and systemic fungicides.

Plant Disease control by Biological methods:- Biological control involves the use of one living organism to control another. 
Biological Control Agents:-
a Parasitoids 
b. Pathogens 
c. Predators 
d. Antagonists of Plant Diseases 
a Parasitoids:-
> Each parasitoids requires only one host, which it kills for its development into a free living adult. 
> Parasitoids are of the same size as the hosts , or sometimes even smaller. 
> Mechanism:-
- The Female parasitoid lays eggs inside or on an insect host. 
- Legless larva on hatching feed on the hosts internally or externally. 
- Many adult parasitoids feed on nectar or pollen and serve as important pollinators. 
> Examples:- Trichogramma,Ichneumoid,Scelionoid,Braconid, Encryrtid,Eulophid,Chalcid wasps and Tachinid Flies.
> Revolution of Trichogramma chilonis:-
- Trichogramma chilonis has been successfully released in Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, Gujrat , Uttrakhand , Uttar Pradesh, Bihar , Karnataka, Tamil Nadu ,Maharashtra and few other states. 
- It has given 56-82% protection against the sugarcane tissue borers.
b. Pathogens:-
> Pathogens are disease causing organisms e.g. Bacteria, Fungi, Viruses ,Protozoa and Nematodes in Insect Pests which kill their host or debilitate the future generation. 
> Mechanism:-
- The infected insects are unable to feed properly ,remain stunted, lose their body colour and get paralysed. 
- Dead insects are often found hanging on the plants, or a fungal growth on the body of dried insect could be easily located in the field. 
- Caterpillar, Pseudoplusia includens , killed by entomopathogenic fungus Nomuraea rileyi , white-disease in soybean crop.
c. Predators:-
> These are free living and larger in size than their prey, requiring several preys to complete their life cycle. 
> Some smaller predators release a powerful poison, use a trap or hunt in groups to be more effective. 
> Mechanism:- 
- Green lacewings (very common and important predator of crop pests). 
- The female lays small pale green, oval shaped eggs at the end of long silken stalks, which ultimately turns grey.
- The larva have well developed legs and pincer like jaws with which they suck the body fluids from the prey.
d. Antagonists of Plant Diseases:- The microorganisms used in biological suppression of plant diseases which grow in association with plant diseases are termed as antagonists. 
An antagonist microorganism adversely affects the disease causing organism by following:- 
i. Competition:- The competition which takes place between two organisms in terms of nutrients etc. 
ii. Antibiosis:- An association between organisms that is injurious to one of them. Antibiosis, is provided by marigold (Tagetes species) roots, which release terthienyls, chemicals that are toxic to several species of nematodes and fungi.
iii. Hyperparastism:- The parasitic habit of one species upon another parasitic species which is harmful to one of them. 
iv. Mycoparasitism:- A parasitism of a fungus(host) by another fungus(mycoparasite). Trichoderma harzianum, used as seed treatment against pathogenic fungus(Sclerotium rolfsii) on chickpea and sugarbeet.

Plant Disease control by Resistant varieties:- Using resistant varieties is the most efficient way of controlling vegetable diseases. Make an effort to buy resistant varieties when they are available. 
> The following terms are important in a discussion of crop resistance:
i. Immunity
ii. Resistance
iii. Tolerance
> Immunity is the rule in the plant kingdom; most plants are immune to most pathogens. Therefore, one does not have to worry that the black spot on roses will appear next year on the garden tomatoes.
> Resistance, strictly speaking, refers to the lower disease levels seen in some cultivars or varieties of a particular crop species compared to other susceptible cultivars. Always choose resistant varieties when available.
> Tolerance refers to varieties or cultivars that appear to be just as heavily diseased as standard varieties, but which manage to be more productive or vigorous.

Ans.
Pathogen:- A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes.
Major Types of Plant Pathogens:- The breath of diversity among plant pathogens is truly marvellous. You can largely group them into four main categories:
i. Bacteria:- Gram-positive and gram-negative bacteria like _Pseudomonas_, _Xanthomonas_ are prime examples.
ii. Fungi:- They are maybe the most common plant pathogens. _Fusarium_, _Verticillium_, and _Rusts_ fall under this category.
iii. Viruses:- These tiny pathogens cause significant damages like Tobacco Mosaic Virus.
Parasitic Plants: Some plants tend to be parasitic, for example, _Dodder_. 
iv. Nematodes:- Nematodes are thread-like roundworms that live in a wide range of environments including soil and fresh and salt water. There are species of nematodes that feed on fungi, bacteria, protozoans, other nematodes, and plants. They can also parasitize insects, humans, and animals.