OBJECTIVE QUESTION

Here are the questions and their correct options:

(a) Fungi are always:
(iv) Heterotrophic

(b) Mycology is the study of-
(ii) Fungi

(c) Sexual reproduction takes place in:
(ii) Basidiomycetes

(d) Which of the following diseases is caused by a fungus?
(ii) Rust of wheat

(e) Mycology is the study of-
(ii) Fungi

SUBJECTIVE QUESTIONS

Here are detailed answers to your questions:

2. Describe the Life Cycle of Puccinia

Puccinia is a genus of fungi that includes many plant pathogens, notably those causing rust diseases in crops such as wheat, barley, and oats. The life cycle of Puccinia typically involves multiple stages and a variety of hosts, which can be summarized as follows:

• 1. Spore Germination: The life cycle begins with the germination of urediniospores, which are the asexual spores. These spores are released from the host plant during favorable conditions, such as warm, moist weather. Upon landing on a suitable host plant, they germinate and form hyphae, which penetrate the plant tissues.
• 2. Asexual Reproduction: Once the hyphae establish themselves within the host, they produce more urediniospores through asexual reproduction. These spores can spread to other parts of the same plant or to nearby plants, leading to further infection. This stage can continue throughout the growing season, resulting in numerous cycles of infection and spore production.
• 3. Sexual Reproduction: Under certain environmental conditions, such as the onset of winter or drought, Puccinia switches to sexual reproduction. This involves the formation of specialized structures called telia, which produce teliospores. Teliospores are thick-walled and can survive unfavorable conditions.
• 4. Overwintering: The teliospores can survive through harsh winter conditions. When conditions become favorable in spring, the teliospores germinate to produce basidiospores. This stage marks the transition from the asexual to the sexual phase of the life cycle.
• 5. Basidiospore Dispersal: The basidiospores are released and are typically wind-dispersed. They infect alternate hosts, commonly members of the genus Berberis (barberry plants). In these alternate hosts, the basidiospores germinate and form new hyphae, completing the sexual cycle.
• 6. Infections in Alternate Host: On the alternate host, Puccinia undergoes a different stage of reproduction, forming structures called aecia, which produce aeciospores. These spores can then infect primary hosts (such as wheat), thus completing the life cycle of Puccinia.

This complex life cycle, which involves both asexual and sexual reproduction and multiple hosts, enables Puccinia to adapt to changing environmental conditions and establish itself as a significant plant pathogen.

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3. Citrus Canker

Citrus canker is a bacterial disease caused by the pathogen Xanthomonas citri subsp. citri. This disease affects various citrus species, including oranges, lemons, and limes, leading to significant economic losses in citrus production. Here are the key aspects of citrus canker:

• Symptoms: Citrus canker is characterized by the appearance of raised, corky lesions on the leaves, stems, and fruit of infected citrus plants. These lesions can be yellowish to dark brown in color and may eventually cause premature leaf drop, fruit deformity, and reduced fruit quality.
• Disease Cycle: The bacterium enters the plant through natural openings, such as stomata or wounds caused by insects or mechanical damage. Once inside, it multiplies and spreads through the plant’s vascular system. The disease is particularly favored by warm, humid conditions and can spread rapidly, especially during rainy weather.
• Transmission: Citrus canker spreads primarily through water splashes and wind-driven rain, which disperse bacteria from infected to healthy plants. Insects, such as leafhoppers and aphids, can also act as vectors, facilitating the spread of the disease.
• Management: Managing citrus canker involves several strategies, including:
• Cultural Practices: Implementing good sanitation practices, such as removing infected plant material, helps reduce the spread of the disease.
• Chemical Control: Copper-based bactericides can be used to manage the disease, although their effectiveness can vary depending on the disease stage.
• Resistant Varieties: Developing and planting disease-resistant citrus varieties is a long-term strategy for managing citrus canker.
• Impact: Citrus canker significantly impacts citrus production, reducing yield and fruit quality. In severe cases, it can lead to the abandonment of infected orchards, causing economic losses for growers.

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4. Late Blight of Potato

Late blight of potato is a devastating plant disease caused by the oomycete pathogen Phytophthora infestans. This disease is notorious for causing massive crop losses, particularly during the growing season. Here’s a detailed overview:

• Symptoms: Late blight manifests as dark green or brown lesions on leaves and stems, which can rapidly expand and lead to the death of the plant. Infected tubers may develop dark, sunken lesions and can rot, making them unmarketable.
• Life Cycle: The life cycle of Phytophthora infestans includes both asexual and sexual reproduction:
• Asexual Reproduction: The pathogen primarily reproduces asexually by producing sporangia, which can germinate to form zoospores. These zoospores swim in water, allowing them to infect healthy plant tissues.
• Sexual Reproduction: Under certain conditions, Phytophthora infestans can also undergo sexual reproduction, forming oospores, which can survive in the soil and contribute to disease outbreaks in subsequent growing seasons.
• Environmental Conditions: Late blight thrives in cool, wet conditions. High humidity and prolonged leaf wetness are conducive to disease development. This makes the disease particularly problematic during rainy seasons or in regions with high moisture levels.
• Spread and Transmission: The disease can spread rapidly within fields and between fields through infected seed potatoes, water, wind, and mechanical means. Farmers often see late blight outbreaks in years with conducive weather conditions.
• Management Strategies: Effective management of late blight involves:
• Cultural Practices: Crop rotation, removal of infected plant debris, and proper spacing to improve air circulation can help reduce disease incidence.
• Resistant Varieties: Planting resistant potato varieties is an effective long-term strategy to combat late blight.
• Chemical Control: Fungicides are commonly used for disease management, particularly when weather conditions are favorable for disease development. Regular monitoring and application of fungicides can help protect crops.
• Historical Impact: The late blight outbreak in Ireland during the 1840s led to the Great Famine, resulting in significant social and economic consequences. This highlights the importance of understanding and managing this pathogen effectively.

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5. What are the Functions of Mycorrhiza?

Mycorrhiza refers to a symbiotic association between fungi and plant roots, which is crucial for the health and growth of many plants. There are two primary types of mycorrhizal associations: arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM). The functions of mycorrhiza include:

• Nutrient Uptake: Mycorrhizal fungi enhance the absorption of essential nutrients, particularly phosphorus, nitrogen, and micronutrients. The extensive hyphal network of the fungi increases the surface area for nutrient absorption beyond the root system, allowing plants to access nutrients that are otherwise unavailable.
• Water Absorption: Mycorrhizae improve water uptake, especially during drought conditions. The fungal hyphae can extract water from the soil more effectively than plant roots alone, helping plants maintain turgor pressure and reducing water stress.
• Soil Structure Improvement: The presence of mycorrhizal fungi helps improve soil structure by binding soil particles together, enhancing soil aggregation. This leads to improved soil aeration, drainage, and water retention, benefiting plant growth.
• Disease Resistance: Mycorrhizal associations can enhance plant resistance to soil-borne pathogens and diseases. The fungi may produce antimicrobial compounds or induce systemic resistance in the host plant, helping to protect against infections.
• Plant Growth Promotion: Mycorrhizal fungi can produce growth-promoting hormones that stimulate plant growth. This symbiotic relationship often results in improved plant vigor, increased biomass, and enhanced root development.
• Carbon Sequestration: Mycorrhizal fungi play a role in carbon cycling by aiding in the sequestration of carbon in the soil. They contribute to the formation of stable soil organic matter, which is essential for soil health and fertility.
• Biodiversity Support: Mycorrhizal associations contribute to plant community diversity by facilitating the establishment of various plant species. Healthy mycorrhizal networks can support the coexistence of multiple plant species, enhancing ecosystem stability.

In summary, mycorrhizae are essential for plant health and growth, providing numerous benefits that enhance nutrient and water uptake, improve soil structure, and promote overall plant vigor. The symbiotic relationship between fungi and plant roots plays a vital role in maintaining healthy ecosystems and agricultural productivity.