Plant Pathology Pre-class Survey

The correct answer is "Living" because disease-causing agents, also known as pathogens, are typically microorganisms such as bacteria, viruses, fungi, or parasites that are living organisms. These pathogens can invade and replicate within a host organism, causing various diseases and health problems.

Obligate biotrophs are pathogens that rely entirely on a living host plant for their growth and survival. They cannot grow in artificial culture or in the soil, and they do not require oxygen. These pathogens establish a close relationship with their host plants, obtaining nutrients from them without causing significant damage. They have evolved specialized mechanisms to suppress the plant's defense responses and manipulate its physiology to create a favorable environment for their growth.

The correct answer is H2, P2, E2. This combination represents a susceptible host (H2), a virulent pathogen (P2), and a conducive environment (E2). In the disease triangle concept, all three components must be present for a disease to occur. A susceptible host is necessary for the pathogen to infect, a virulent pathogen is necessary to cause the disease, and a conducive environment provides the conditions for the disease to develop and spread. Therefore, the combination of H2, P2, E2 fulfills all the requirements for the disease triangle.

Viruses are the smallest plant pathogens, followed by bacteria, fungi, nematodes, and parasitic plants, which are the largest.

Fungi and bacteria can be disseminated from one place to another through various means. Wind can carry their spores or particles, allowing them to travel through the air. Water can transport them, especially in the case of aquatic environments or during rainfall. Infected plant material, such as leaves or fruits, can carry these microorganisms and spread them when moved or transported. Infested farm equipment, like tools or machinery, can also transfer fungi and bacteria from one area to another. Lastly, these microorganisms can be present in or on seeds, leading to their dissemination when the seeds are dispersed or planted elsewhere.

The correct answer includes all of the appropriate plant disease management strategies for fungal diseases. Resistance (host genetics) refers to breeding plants that are resistant to fungal infections. Eradication (eliminate pathogen) involves removing or destroying infected plants to prevent the spread of the fungus. Protection (chemicals) involves using fungicides to control fungal infections. Exclusion (quarantines) involves isolating infected plants to prevent the spread of the fungus. Avoidance (unfavorable conditions) refers to creating conditions that are unfavorable for fungal growth and infection. Therapy (curative injections) involves treating infected plants with injections to cure the fungal infection.

Wheat stem rust is an example of a polycyclic disease. Polycyclic diseases are those that have multiple cycles of infection and reproduction within a single growing season. Wheat stem rust is caused by a fungus called Puccinia graminis and is characterized by the formation of reddish-brown pustules on the stems and leaves of wheat plants. The fungus produces spores that can spread and infect other plants, leading to multiple cycles of infection and disease development throughout the growing season.

Plant virus genomes are composed of single-stranded RNA. This means that they can directly function as mRNA (messenger RNA) as soon as they are uncoated in the plant cell. Unlike double-stranded DNA, which needs to be transcribed into mRNA before it can be translated into proteins, single-stranded RNA can be immediately utilized for protein synthesis.

A haustorium is a feeding structure found in parasitic plants. It is a specialized organ that allows the parasite to extract nutrients from the host plant. The haustorium penetrates the host plant's tissues and forms a connection, through which the parasite absorbs water, minerals, and other essential substances. This feeding structure is crucial for the survival and growth of the parasite, as it enables them to obtain the necessary resources from the host plant.

Primary pathogens are capable of surviving in a dormant state during both winter and summer seasons. They cause original infections in the spring or autumn when favorable conditions for growth and reproduction are present. Secondary pathogens, on the other hand, rely on a host already infected by a primary pathogen to cause infection. Tertiary pathogens are not commonly recognized terms in the context of pathogens. Repeating spore stage does not accurately describe the behavior of a pathogen surviving dormant in winter or summer.

Bacterial ooze and fungal structures are both signs of a plant disease. Bacterial ooze refers to the presence of a slimy substance that is produced by bacteria as a result of infection. Fungal structures, on the other hand, are visible structures produced by fungi during their life cycle, such as spores or fruiting bodies. These signs indicate the presence of pathogens and can help in diagnosing and treating plant diseases. Necrosis, chlorosis, and wilting are symptoms of plant diseases, rather than signs, as they are the visible effects or changes that occur in the plant due to the disease.

The given answer includes all the appropriate plant disease management strategies for bacterial diseases. Resistance (host genetics) refers to breeding plants that are resistant to the bacteria. Eradication (eliminate pathogen) involves removing or killing the bacteria from the plants or the environment. Protection (chemicals) refers to the use of chemicals such as pesticides to protect plants from bacterial diseases. Exclusion (quarantines) involves isolating infected plants to prevent the spread of the bacteria. Avoidance (unfavorable conditions) refers to creating conditions that are unfavorable for bacterial growth. Therapy (curative injections) involves treating infected plants with curative injections to help them recover from the bacterial disease.

The given answer, "R1: Avr1," illustrates the GENE-FOR-GENE concept because it shows that the host plant with the resistance gene R1 can recognize and respond to the avirulence gene Avr1 in the pathogen. This recognition triggers a defense response in the host plant, leading to resistance against the pathogen. This interaction demonstrates the specific recognition and response between a resistance gene in the host and an avirulence gene in the pathogen, which is the central concept of the GENE-FOR-GENE theory.

Necrosis, chlorosis, and galls are all symptoms of plant diseases. Necrosis refers to the death of plant tissue, often resulting in black or brown discoloration. Chlorosis is the yellowing of plant leaves due to a lack of chlorophyll. Galls are abnormal growths on plant tissues caused by pathogens, such as bacteria or fungi. These symptoms indicate that the plant is affected by a disease and can help diagnose the specific problem.

Horizontal resistance refers to the resistance exhibited by a plant against a wide range of pathogens or pests. Quantitative resistance and polygenic resistance are examples of horizontal resistance. Quantitative resistance is a type of resistance controlled by multiple genes and provides partial protection against a pathogen or pest. Polygenic resistance is also controlled by multiple genes and provides broad-spectrum resistance against a range of pathogens or pests. Both types of resistance are considered horizontal because they are effective against multiple strains or races of pathogens or pests. Single-gene resistance and race-specific resistance, on the other hand, are examples of vertical resistance, which are effective against specific strains or races of pathogens or pests.

Fungi can infect plants through various means. They can enter through wounds in the plant's tissue, such as cuts or injuries. Fungi can also directly penetrate the plant's cells and tissues, breaking through the outer barriers. Additionally, natural openings in plants, such as stomata or lenticels, can provide entry points for fungal infection. Lastly, fungi can be transmitted to plants through vectors, such as insects or other organisms that carry and spread fungal spores.

A definition of PLANT DISEASE should include the concepts of disruption of normal functioning, constant irritation, biotic agent, and abiotic agent. This means that a plant disease involves a disturbance in the normal functioning of a plant, causing constant irritation to the plant. It can be caused by either a biotic agent, such as a pathogen or pest, or an abiotic agent, such as environmental factors like temperature or nutrient deficiencies.

Bacteria can infect plants through wounds, natural openings, and vectors. When a plant is wounded, such as by a cut or insect feeding, bacteria can enter through the damaged tissue. Natural openings, such as stomata and lenticels, can also provide entry points for bacteria. Additionally, vectors such as insects or other organisms can carry bacteria and introduce them to plants when they feed or come into contact with plant tissues. These various pathways allow bacteria to infect plants and cause diseases.

Nematodes can infect plants through various means. They can enter through wounds in the plant tissue, such as cuts or injuries. They can also directly penetrate the plant's cells and tissues, gaining access to the plant's internal structures. Additionally, nematodes can exploit natural openings in the plant, such as stomata or root hairs, to invade and infect the plant. Finally, nematodes can be transmitted to plants by vectors, such as insects or other organisms, which carry and introduce the nematodes into the plant.

Facultative fungi and bacteria can survive in between cropping cycles by utilizing various sources. Crop residue provides organic matter and nutrients for their survival. Soil acts as a reservoir, providing a suitable environment and nutrients. Within vectors, such as insects or animals, these microorganisms can hitch a ride and survive. Reservoir hosts, which are organisms that can harbor and transmit the microorganisms, also contribute to their survival. Overall, the combination of crop residue, soil, vectors, and reservoir hosts allows facultative fungi and bacteria to persist during cropping cycles.

Viruses can infect plants through wounds and vectors. Wounds provide an entry point for the virus to enter the plant's tissues, allowing it to infect and spread within the plant. Vectors, such as insects or other organisms, can carry the virus from one plant to another, transmitting it through their feeding or contact with the plants. Both methods contribute to the spread and infection of viruses in plants.

The correct answer for the question is Resistance (host genetics), Eradication (eliminate pathogen), Exclusion (quarantines), and Avoidance (unfavorable conditions). These strategies are appropriate for managing viral diseases in plants. Resistance refers to using host genetics to develop plants that are resistant to the virus. Eradication involves eliminating the pathogen from the affected plants or the entire area. Exclusion involves implementing quarantines to prevent the entry and spread of the virus. Avoidance focuses on creating unfavorable conditions for the virus to thrive, such as altering environmental factors. These strategies can help prevent and control viral diseases in plants.

The appropriate plant disease management strategies for nematode diseases include resistance (host genetics), eradication (eliminate pathogen), exclusion (quarantines), and avoidance (unfavorable conditions). Resistance refers to using plants that are genetically resistant to the nematode disease. Eradication involves eliminating the nematode pathogen from the affected area. Exclusion involves implementing quarantines to prevent the spread of nematodes. Avoidance involves creating unfavorable conditions for nematode growth and reproduction. Therapy (curative injections) and protection (chemicals) are not appropriate strategies for managing nematode diseases.