2017 Solved Old Paper (BOT - 201) New
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Ans.
General principles of classification of Fungi:-
A. Nutrition
B. Thallus
C. Flagellation
D. Reproduction
A. Nutrition:-
- All fungi are heterotrophic.
- There are 3 types of nutrition in fingi:-
a. Parasitic Fungi
b. Saprophytic Fungi
c. Symbiotic Fungi
a. Parasitic Fungi:- These are fungi that can invade a living host and obtain nourishment, often causing damage to the function and structure of the host.
- Based upon nature they are of 2 types:
i. Obligate parasites:- A parasite that cannot complete its life-cycle without exploiting a suitable host. Eg. Albugo
ii. Facultative parasites:- A parasite that is normally saprophytic but may occasionally be parasitic under certain conditions. Eg.- Pythium, Fusarium
b. Saprophytic Fungi:- It is the largest group of fungi, grow on dead organic matter such as fallen trees, cow patties, dead leaves, and even dead insects and animals. Saprophytic fungi play an important role in decomposition of organic matters and nutrition cycling.
- Based upon nature they are of 2 types:
i. Obligate saprophytes:- A parasite that relies completely on dead organic matter. Eg.- Mucor, Yeasts, Mushrooms
ii. Facultative saprophytes:- A parasite which becomes saprophytic in the absence of host is called facultative saprophyte. Eg.- Smuts
c. Symbiotic Fungi:- It is the close relationship between fungi and other organism in which both partners share similar habitat and remain depended on each other equally for survival.
Fungi show 2 types of symbiotic relationships:
i. Lichens:- It is a symbiotic association of fungi with algae. Fungi support the algae by providing protection and assist in the absorption of water. In reverse, algae provide food to fungi that lack chlorophyll pigments.
ii. Mycorrhiza:- It is a symbiotic association of fungi with roots of higher plants. Their major role is to enhance nutrient and water uptake by the host plant by exploiting a larger volume of soil than roots alone can do. the large mass of fungal hyphae acts as a virtual root system for the plants, increasing the amount of water and nutrients that the plant may obtain from the surrounding soil. In reverse, the roots provide essential nutrients for the growth of the fungi.
C. Thallus:- There are 2 types of thallus in fungi -
a. Unicellular Thallus:- It is of two type -
i. Holocarpic thallus:- Here the entire cell becomes changed into a reproductive structure. Eg.-Synchytrium, Yeasts
ii. Eucarpic thallus:- Here the the lower part of the cell is differentiated into rhizoid to absorb food material and upper part is differentiated into reproductive structure. Eg.- Chytridium
b Multicellular Thallus:-
Hypha:- One of the long slender tubes that develop from germinated spores and form the structural parts of the body of a fungus.
Mycelium:- It is the mass of interwoven filamentous hyphae that represent the thallus of a fungus.
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Tyes of Hapha:- 2 types based upon absence or presence of septation -
i. Aseptate Hypha:- Hyphae that do not have cross-walls are called as aseptate. These types of hyphae are also called as coenocytic. They represent a more primitive form of fungi. Eg.- Lower fungi
ii. Septate Hypha:-Hyphae that have cross-walls are called as septate. These types of hyphae are also called as cellular. They represent a more advanced form of fungi. Eg.- Higher fungi
C. Flagellation:-
- Flagellum:- It is a hair-like structure that acts primarily as an organelle of locomotion in the cells of many living organisms.
- Flagella are found only in lower fungi. They are completely absent in higher fungi.
- Each flagellum has 9 + 2 arrangement in structure. In this arrangement, 9 fused pairs of microtubules on the periphery forms a cylinder along with the 2 unfused microtubules at the center.
- There are 2 types of flagella in lower fungi:-
a. Acronematic (Whiplash type or Smooth type):- The mastigonemes are absent on the outer surface of flagellum. It is of two types -
i. Blunt ended:- The distal ends of the flagellum is not extended outward.
ii. With end piece:- The distal ends of the flagellum is extended as a terminal, naked, axial filament.
b. Pantonematic (Tinsel type or Rough type or Flimer type):- Two or more rows of mastigonemes are present on both sides of the flagellum.
3 types of reproduction is observed in fungi -
1. Vegetative reproduction:-
i. Fragmentation
ii. Fission
iii. Budding
2. Asexual reproduction:- 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:-
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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
3. Sexual reproduction:-
Types of Sex organs (Gametangia):- 2 type -
a. Isogametangia:- When gametangia are similar in structure and they can not be differentiated into male and female. Eg.- Zygomycetes, Trichomycetes
b. Heterogametangia:- When gametangia are different in structure and they can be differentiated into male and female. These are of 2 types -
I. Male sex organ:- It is always called as Antheridium.
II. Female sex organ:- 2 types -
i. Oogonium:- Found in members of Oomycetes.
ii. Ascogonium:- Found in members of Ascomycetes. It has two shpes -
- Cylindrical:- Trichogyne absent.
- Spherical:- Trichogyne present.
Mechanism of Sexual Reproduction:- It includes 3 main steps -
a. Plasmogamy
b. Karyogamy
c. Meiosis
a. Plasmogamy:- It is a fusion of protoplasms of two-parent cells in which nuclei remain unfused and finally bringing two haploid nuclei in the same cell. The pair of two nuclei is called as dikaryon.
There are 5 methods of plasmogamy in fungi:-
i. Planogametic copulation
ii. Gametangial contact
iii. Gametangial copulation
iv. Spermatization
v. Somatogamy
b. Karyogamy:- It is the fusion of two haploid nuclei and the formation of a diploid nucleus, which is called as synkaryon.
- In lower fungi (Zygomycetes & Oomycetes) karyogamy takes place immediately after plasmogamy.
- In higher fungi (Ascomycetes & Basidiomycetes) there is time gap and space gap between plasmogamy and karyogamy.
Time gap:- It is an interval of time between plasmogamy and karyogamy during which a dikaryophase exists.
Dikaryophase:- This is the phase of fungi in which most of the cells of fungi contain dikaryons that are formed due to plasmogamy. This is seen in higher fungi.
Space gap:- Plasmogamy and Karyogamy occurs at different places. This interval of space is called as space gap.
c. Meiosis:-
- In lower fungi (Zygomycetes & Oomycetes) there is time gap between karyogamy and meiosis. During this time interval synkaryon remain dormant in resting stage.
- In higher fungi (Ascomycetes & Basidiomycetes) meiosis takes place immediately after karyogamy.
Ans.
Role of fungi in industries:-
1. Alcohol Production:- Alcoholic fermentation by fungi is the basis of brewing industry. The enzyme zymase of microorganisms like yeast is responsible for alcohol production. Wines are produced from grapes or other fruits by Saccharomyces ellipsoideus with about 14% alcohol concentration. Beer is brewed from barley malt by Saccharomyces cerevisiae with 3-8% alcohol production.
2. Organic acid Production:- Many fungi are used in the commercial production of different organic acids.
3. Fungi as Food:- Fungi are used as food by humans from a long time ago.
> Fruit bodies of some fungi, like Mushroom and truffles are used as food due to their high protein content (21-30% on dry weight) and have good amount of lysine, an amino acid; minerals like Na, Ca, K and P; Vitamins like B, C, D and K and very little amount of fat. These are recommended as ideal foods for heart patients and diabetes.
> The above-mentioned fungi can grow artificially at the commercial level. Mushroom cultivation has recently gained considerable popularity and has contributed to the national economy in some East Asian
countries.
4. Fungi as Fodder:-
> Yeast that is used as animal feed it is a microbial proteins synthesized by yeast in which digestibility amino acid content higher than an animal routine does has a high biological value as compared to other feed.
> Inactive dry yeast fodder increases bioavailability of protein as they contain essential amino acid.
> Composition of fodder yeast contain 10 essential amino acid. On the content of amino acids fodder yeast similar to proteins of animal origin
> Feed yeast contain Vitamin B (rgulate fat metabolism) rich source of Vitamin D2 (5000-12000 IU/Kg Fd .yst).
> Ash of fodder yeast also contain valuable animals and birds macro and micro elements P, K, Ca, Fe, Mg, S, Na, Cu and others.
> Yeast commonly used commercially strain of Candida utilis,(torula yeast) often called as Torulopsis utilis.
> Other yeast used commerically or studied extensively in laboratory include C.tropicalis and Saccharomyces cerevisea.
Ans.
Mushroom cultivation:-
Mushroom:-
> Mushrooms are the eukaryotic, spore bearing organisms, macro-fungi lacking chlorophyll and
grow on dead decomposed matter as saprophytes.
> They derive nutrients through their mycelia. This mycelium forms the fleshy structures, the fruit bodies, which are generally called the mushrooms.
> There are more then 10,000 verities of mushroom out of which only 200 verities identified as edible variety.
Varieties of Mushrooms:- We can grow four varities of mushroom depending upon the climatic condition as:
i. Oyster Mushroom (Sept-April)
ii. Paddy Straw Mushroom (May-Sept)
iii. Milky Mushroom (Sept-April)
iv. Button Mushroom (Nov-Feb)
Cultivation of Button mushroom:- The most popular kind of mushrooms are button mushrooms, often referred to as white mushrooms, baby mushrooms, and cultivated mushrooms. These mushrooms can be consumed raw or cooked, and are frequently added to salads, soups, and as toppings for pizza. In the sixteenth century, button mushrooms were first grown. Button mushrooms make up 85% of the annual production of mushrooms.
Following is a process to grow mushroom:-
1. Compost:-
> The first stage in cultivating button mushrooms is composting.
> This procedure is carried out in public.
> On neat concrete platforms, button mushrooms are raised.
> Compost is prepared in the two types listed below:
a. Natural compost:-
- Natural compost is produced by nature.
- When producing compost for button mushrooms, some natural ingredients are wheat straw, horse manure, gypsum, and chicken manure.
- The compost yard should be evenly covered with a mixture of all the components.
- After that, moisten the prepared compost with a water sprayer.
b. Synthetic Compost:-
- For synthetic compost, we needed urea, gypsum, wheat straw, bran, and ammonium nitrate / ammonium sulphate.
- To begin, trim the staw to a length of 8 to 20 cm.
- Now cover the compost with a fine layer of cut straws and mist it with water.
- You must now thoroughly combine the bran, calcium nitrate, urea, gypsum, and other ingredients.
2. Filling the compost trays:-
> The compost that has been processed is a deep brown tint.
> The compost shouldn't be too damp or too dry when you put it in trays.
> Spray some water on the compost if it's dry.
> Allow some water to evaporate if it is excessively wet.
> You can choose the size of the compost-spreading trays to suit your needs.
> The depth must be between 15 and 18 cm.
> Make sure the trays are constructed of softwood as well.
> Compost must be poured into the trays to the rim and spread out evenly.
3. Spawning:-
> Spawning is the following stage in the cultivation of button mushrooms.
> It entails planting mycelium in the beds.
> There are two methods for spawning:
i. The first is to distribute compost on the tray bed.
ii. The second is to mix mycelium with compost before spreading it on the tray.
> After sprinkling the tray with water and spawning, you must cover it with newspaper to keep the moisture there.
4. Casing:-
> The tray must now be covered with a heavy layer of dirt.
> This soil can be created by mixing garden soil and decomposing cow manure.
> Casing soil is the term for this soil. This casing soil may hold a lot of water.
5. Harvesting:-
> The cap should be gently torn off during harvest.
> To do this, hold it gently between your forefingers, press it into the ground, and then twist it off.
> Cut off the base of the stalk where mycelial threads and dirt granules adhere.
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:- The methods of formation of heterokaryotic mycelium are described earlier under ‘heterokaryosis.
ii. Nuclear Fusions and Multiplication of the Diploid Nuclei:-
- Nuclear fusion in somatic heterokaryotic hyphae was first noted by Roper (1952) in Aspergillus nidulans.
- Nuclear fusion may occur between genetically similar and dissimilar nuclei, resulting in the formation of homozygous and heterozygous diploid nuclei, respectively.
- Diploid heterozygous nuclei are formed very rarely (at a frequency of one in a million).
- In such hyphae, five types of nuclei are present- 2 types of haploid nuclei, their two types of homozygous diploids, and the one type of heterozygous diploids.
iii. Mitotic Crossing Over:-
- Crossing over is a phenomenon which occurs during meiosis and gives rise to new linkage of genes, gene recombination. A similar mitotic crossing over occurs during the multiplication of the diploid heterozygous nuclei, though at a low frequency of 10-2 per nuclear division.
- However, in some other fungi e.g., Penicillium chrysogenum and Aspergillus niger, the frequency of mitotic crossing over is as high as during meiosis in sexual reproduction. (Both species lack sexual reproduction.) Mitotic crossing over is the most important, or ‘key’ event in the parasexual cycle, as it is during this step that genetic recombination occurs.
iv. Sorting Out of Diploid Strains:- The segregation of the diploid strains occurs when uninucleate diploid conidia are formed. The colonies that are formed by diploid conidia are recognized by various methods, e.g., higher DNA content and bigger size of the conidia and certain phenotypic characters of the colony.
v. Haplodization:-
- The diploid colonies show appearance of sectors on the Petri plate, which produce haploid conidia. This indicates that some diploid nuclei must have undergone haplodization, forming haploid nuclei, which later get sorted out in haploid conidia.
- Some of these haploids are genetically different from the original haploid parental nuclei. This is because of the recombination that occurred during the mitotic crossing over.
- Haplodization occurs at a constant frequency of 10-3 per nuclear division. The haplodization occurs not by a reduction division (meiosis), but by aneuploidy, a phenomenon in which chromosomes are lost during mitotic divisions.
- It happens in the following manner. During mitosis of the diploid nucleus, the chromatids fail to separate (non-disjunction) in the anaphase stage.
- One daughter nucleus gets one chromosome more (2n + 1), while the other gets one chromosome less (2n – 1) than the normal 2 sets of chromosomes (2n). Both the daughter nuclei are called aneuploidy. The deficient aneuploid nucleus (2n – 1) may lose more chromosomes in the successive mitotic division and finally reduce to haploid state (n).
- Mitotic crossing over and haplodization also occur with the diploid homozygous nuclei, but since the two nuclei are similar, crossing-over products or the haploid nuclei formed by haplodization, are genetically no different from the haploid parent nuclei.
- The parasexual cycle, thus, like the sexual cycle, involves plasmogamy, karyogamy and haplodization, but not at a specified time or place. Every step differs drastically.
Significance of Parasexuality:-
- Parasexual cycle is of importance in industrial processes.
- Several fungi which are used in various industrial processes belong to fungi imperfecti or Deuteromycetes and in these fungi only parasexual cycle operates.
- New and better strains of these fungi are obtained by mutation through parasexual cycle.
- The strains of desirable characters can be developed through mitotic recombination.
- Parasexuality can also be applied in the analysis of genetic and physiologicaln processes of perfect and imperfect fungi.
- Parasexual cycle has also been successfully employed in genetic control of pathogenicity and host-range in several species of Fusarium.
Pontecarvo’s (1958) idea of parasexual cycle
Ans.
Fusarium:-
1. Classification:-
Kingdom:- Myceteae
Division:- Amastigomycota
Sub division:- Deuteromycotina
Class:- Deuteromycetes
Sub-class:- Hyphomycetidae
Order:- Moniliales
Family:- Tuberculariaceae
Genus:- Fusarium
2. Habit and Habitat:-
> Fusarium is represented by large number of species which occur both in temperate and tropical regions of the world.
> Majority of the species are saprophytic, some are mild facultative parasite while some species are parasitic and cause serious diseases like wilt or ‘rot’ of economically important plants.
3. Thallus Structure:-
> Mycelium is branched, sepate, hyaline or coloured, inter-or intracellular and uninucleate to multinucleate.
> Hyphae invade the tracheids and vessels of xylem, ramify there, produce toxic substances and block them completely. As a result the plants wilt and die.
4. Reproduction:- It takes place by the formation of asexual spores. These are:
a. Micro conidia
b. Macro conidia
c. Chlamydospores
a. Micro conidia:-
> The micro conidia and macro conidia are produced in same sporodochia. These sporodochia develop on the surface of stem, leaves and other parts of the host plant.
> The fungal mycelium collects near the surface of the host tissue as anpseudoparenchymatous mass. It gets exposed by the rupturing of the epidermis.
> From the fungal hyphae arise many short and cylindrical structures. These are conidiophores.
> The ultimate branches of conidophores which produce conidia are called phialides.
> The phialides are subulate i.e. owl shaped and have some kind of heel (characteristic of Fusarium).
> Micro conidia are small, unicellular or bi-celled, spherial or oval in shape.
> Their size varies from 5×15 µ x2−4 µ.
> They are borne single or in chains on the conidiophores by abstraction method.
> Micro conidia are produced in vast numbers.
> They are easily disseminated by wind and after falling on the suitable substratum, they germinate and infect the host plants.
b. Macro conidia:-
> The macro conidia are long, sickle or crescent shaped, multi-septate (3-5 septa), pointed at the end and broad in the middle.
> They measure 15-50 µ in length and 3-5 µ in breadth.
> Macro conidia are produced in vast numbers.
> They are easily disseminated by wind and after falling on the suitable substratum, they germinate and infect the host plants.
c. Chlamydospores:-
> Under relatively starvation and dry conditions, the mycelial hyphae produce ovoid or spherical thick walled cells. These are called chlamydospores.
> They occur either single or in chains and may be terminal or intercalary in position.
> After maturity they get separated from the parent hyphae and act as resting spores, under favourable conditions they germinate by means of germ tubes to form a fresh mycelium.
> The pseudoparenchymatous mycelium of Fusarium often forms black, compact bodies known as sclerotia. They act as storage organ and also serve as means of perennation and vegetative reproduction.
Ans.
Ergot disease of Bajra:-
Pathogen:- Claviceps fusiformis
Symptoms:-
> Small droplets of pinkish sticky fluid oozes out of the spikelets. The affected spikelets turn black and several such dark sticky patches are seen on the earhead.
> Grain formation is inhibited.
> The honey dew contains large number of hyaline single celled conidia.
> Later infected ovaries get converted into sclerotia.
Management:-
1. Seed treatment:-
> Removal of ergot / sclerotia to prevent primary infection Dissolve 1 kg of common salt in 10 litres of water. Drop the seeds into the salt solution. Remove the ergot and sclerotia affected seeds which
will float. Wash seeds in fresh water 2 or 3 times to remove the salt on the seeds. Dry the seeds in shade.
> Treat the seeds with Thiram @ 2g /kg of seed.
2. Spray of Fungicides:- Spray any one of the fungicides like Carbendazim 500g or Mancozeb
1000g /ha when 5 - 10% flowers have opened and again at 50% flowering stage.
Smut of Bajra:-
Pathogen:- Tolyposporium penicillariae
Symptoms:-
> The disease becomes apparent at the time of grain set.
> A few grains, sporadically distributed on the earhead are replaced by green to black sori, which are much bigger than normal grains.
> The sorus wall is tough, surrounding the powdery mass of smut spores which are in balls.
> Favourable Conditions:- High relative humidity; Successive cropping with pearlmillet.
Management:-
> The only control measures recommended strongly for this disease are the removal of smutted ears, use of clean seeds, hot weather deep ploughing, field sanitation, and crop rotation.
> Attempts are required to raise resistant varieties of this crop against smut disease.
Ans.
Early Blight of Potato:-
Pathogen:- Alternaria solani
Symptoms:-
> It is present in both hills & plains.
> Brown-black necrotic spot-angular, oval shape characterized by concentric rings.
> Several spot coalesce & spread all over the leaf.
> Shot holes on fruits.
Management:-
> Disease free seed tubers should be used for planting.
> Removal and destruction of infected plant debris should be done because the spores lying in the soil are the primary source of infection.
> Very early spraying with Zineb or captan 0.2% and repeating it for every 15 – 20 days gives effective control.
> The variety Kufri Sindhuri possesses a fair degree of resistance.
Ans.
Crop rotations:-
Introducvtion:-
> Crop rotation is the practice of growing a variety of crops in the same area over a number of growing seasons.
> It reduces reliance on a single set of nutrients, pest and weed pressure, and the likelihood of developing resistant pests and weeds.
> It is the process of producing a variety of crops in the same place over the course of several growing seasons.
Criteria for Selection of Crops for Rotation:-
> There should be enough moisture.
> Fertilizer, labour, and machine power are all available.
> Marketing and processing facilities.
> Nutrient availability in the soil.
> The crop's duration—short or long.
Principles of Crop Rotation:-
> Due to fact that legumes fix atmospheric nitrogen into the soil and add organic matter to the soil, they should be planted before non-leguminous crops.
> Crops with tap roots (deep rooted crops like cotton) should be followed by crops with fibrous roots (shallow rooted crops like sorghum or maize). This allows for the proper and uniform use of soil nutrients.
> More exhaustive crops should be followed by less exhaustive crops because crops such as potato, sugarcane, maize, and others require more inputs such as better tillage, more fertilisers, more irrigation, and so on.
Types of Crop Rotation:-
1. One-year Rotation:-
> Crop rotation can be carried out for one year, depending on the size of the available plot of land.
> Following harvest, the soil that is suitable for another specific crop will be planted with that crop for the remaining half of the year.
> One crop would be planted during the first half of the year.
> The planting of maize and then mustard is an example of a one-year crop rotation.
> Another example is the planting of wheat first, then rice.
2. Two Years Rotation:-
> The two-year rotation is essentially identical to the one-year rotation, with the exception that more crop options are available and the crop planting rotation would last for two years instead of one.
> Within the course of a two-year crop rotation, there may be a total of two, three, or four crops planted.
> After the prior crop is harvested, the subsequent crops should have all of the nutrients they need.
> A two-year rotation might involve planting successive crops of corn, mustard, sugarcane, and fenugreek as well as subsequent crops of corn, potatoes, sugarcane, and peas.
3. Three Years Rotation:-
> A three-year rotation, as the name suggests, calls for a number of crops to be planted over the course of three years while addressing all of their nutrient needs.
> On the same piece of land, the crops will be planted one after the other in succession.
> The subsequent crop's nutritional needs will be satisfied by the previously planted crops.
> Some examples of three-year crop rotations include:
i. Rice, wheat, mung, and mustard in succession.
ii. Sugarcane and berseem in succession.
iii. Cotton, oat, sugarcane, peas, maize, and wheat in succession.
Advantages of Crop Rotation:-
i. Improves Soil Condition:- Utilizing various crops, especially those with fibrous or tap roots, can improve the soil's chemical, biological, and physical composition. This increases the amount of organic matter and nutrients in the soil as well as its ability to store water.
ii. Improves Soil Structure:- Rotation helps to preserve and improve soil structure. Crops have various root structures and grow to different depths. Rotating exposes the soil not only to shallow depth crops, but also to deep diggers, which gradually deepen the topsoil.
iii. Reduces Soil Erosion and Water Runoff:- Crop rotation can reduce erosion by enhancing the microbial populations and soil tilth. Surface runoff is reduced as a result of the more stable soil structure created.
iv. Reduces Pests and Weeds:- Pests, plants, and insects can't live without their host for very long. Those pests have no chance if you move your crops around and improve the soil structure at the same time.
v. Control of Insects:- Insects tend to enter your plants' leaves and vines as they prepare to reawaken in the spring in search of their favourite meal. When you rotate, these insects come into contact with a plant that they do not feed on.
vi. Disease Prevention:- Plant diseases can over winter enter in plant leaves, roots, and vines beneath your soil. Crop rotation helps to keep these diseases from returning the following year.
vii. Improvement in Water Quality:- Water quality can be improved by reducing sediment loss, as well as dissolved and sediment-attached nutrient and pesticide losses.
viii. Provides Diversification:- Some crops demand less labor and equipment than others. This implies that the workload can be distributed throughout the year. Additionally, it increases the range of the products that can be sold, preventing from having to "place all your eggs in one basket."
ix. Nutrient Uptake Regulation:- As various crops require different nutrients in different quantities, crop rotation aids in boosting the nutrient uptake by plants from the soil. Crop rotation helps the various crops that are planted within the rotation make the most of all the nutrients in the soil, including the nutrients left over from the previous crop that was planted.
Disadvantages of Crop Rotation:-
i. Involves Risk:- Crop rotation requires a significant financial investment each season to purchase various seedlings of the various crops that will be grown.
> Moreover, particular crops demand specific sorts of equipment, thus farmers may have to invest in different types of machinery.
> This implies that the upfront fees can be higher. However, the success of each crop kind is not assured, and one may wind up losing a harvest.
ii. Requires More Skill & Knowledge:- Crop rotation calls for a broader range of abilities and information regarding each type of crop collected because it involves a variety of crops.
> It also calls for various machinery, the operation of which also takes skill. This implies that learning and perfecting this agricultural method will require more time and effort on the part of farmers.
iii. Difference in Growing Conditions:- For monoculture, or a particular type of crop, some places and their temperatures are better suited.
> The specific type of temperature and soil conditions cannot support the growth of any other crops than that particular type of crop.
iv. Obligatory Crop Diversification:- It is mandatory to plant different crops each time for crop rotation to be effective. However, it prevents a farmer from specializing in a particular crop.
Ans.
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.
