Rice Blast Disease Overview
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Rice Blast Disease Overview

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Questions and Answers

What is the primary cause of rice blast in rice plants?

  • Bacteria
  • Nematode
  • Fungus (correct)
  • Virus

    • Which part of the rice plant is commonly affected by rice blast lesions?

  • Flowers
  • Stems
  • Roots
  • Leaves (correct)

    • Which of the following fungi is NOT associated with causing rice blast?

  • Pyricularia oryzae
  • Rhizoctonia solani (correct)
  • Magnaporthe oryzae
  • Magnaporthe grisea

    • What shape are the lesions most commonly associated with rice blast?

    <p>Diamond</p> Signup and view all the answers

    What is the significance of rice as a crop worldwide?

    <p>It is a staple food for hundreds of millions.</p> Signup and view all the answers

    Which of the following options correctly identifies the host plant for rice blast?

    <p>Oryza sativa</p> Signup and view all the answers

    What type of crop failures does rice blast pose a threat to?

    <p>Any type of crop</p> Signup and view all the answers

    Which part of the rice plant is least likely to show symptoms of rice blast?

    <p>Sheaths</p> Signup and view all the answers

    What is the primary structure formed from the appressorium during the infection process in rice?

    <p>Infection peg</p> Signup and view all the answers

    Which environmental conditions most favor the outbreak of rice blast disease?

    <p>Moderate temperatures and high moisture</p> Signup and view all the answers

    During what time period do the first visible lesions typically appear after planting rice?

    <p>45 to 55 days</p> Signup and view all the answers

    What primarily contributes to the severity of rice blast disease?

    <p>The amount of primary inoculum</p> Signup and view all the answers

    What is a common source of primary inoculum during the overwintering phase?

    <p>Volunteer plants</p> Signup and view all the answers

    How does rice typically grow in flooded fields?

    <p>Partially submerged in water</p> Signup and view all the answers

    What happens to infested seeds left on the soil surface after mechanical planting?

    <p>They can produce spores for several weeks.</p> Signup and view all the answers

    Which practice is primarily used for planting rice in the United States?

    <p>Planting as seed by machine</p> Signup and view all the answers

    What structures produce the sexual spores in Magnaporthe oryzae?

    <p>Perithecia</p> Signup and view all the answers

    Which mating system does Magnaporthe oryzae utilize for sexual reproduction?

    <p>Heterothallic with bipolar locus</p> Signup and view all the answers

    What is the common name for the asexual stage of Magnaporthe oryzae?

    <p>Pyricularia oryzae</p> Signup and view all the answers

    What shape are the ascospores produced by Magnaporthe oryzae?

    <p>Hyaline and fusiform</p> Signup and view all the answers

    Under what conditions do conidia of Magnaporthe oryzae typically liberate from lesions?

    <p>After several hours of high humidity</p> Signup and view all the answers

    Where are conidia formed in Magnaporthe oryzae?

    <p>On lesions and culture</p> Signup and view all the answers

    Which of the following rice pathogens is distinct from Magnaporthe oryzae?

    <p>Magnaporthe grisea</p> Signup and view all the answers

    How many septa do the conidia of Magnaporthe oryzae typically have?

    <p>Three</p> Signup and view all the answers

    What condition is associated with the most severe incidence of rice blast disease?

    <p>Moderate daily temperatures with over-fertilization</p> Signup and view all the answers

    How does the extent of rotten neck relate to yield loss in rice?

    <p>1% rotten neck causes 0.5% yield loss</p> Signup and view all the answers

    Which of the following factors does NOT influence the number of spores produced on an individual lesion?

    <p>Age of the rice plant</p> Signup and view all the answers

    What is the result of infection on the neck of the rice plant?

    <p>Reduced seed set on the entire panicle</p> Signup and view all the answers

    What is the main symptom caused by spores infecting the collar of the flag leaf?

    <p>Collar rot</p> Signup and view all the answers

    Which of the following cultivars is considered susceptible to rice blast disease?

    <p>Newbonnet</p> Signup and view all the answers

    What type of discoloration is generally observed with infections of the neck and panicle?

    <p>Nondescript grayish discolorations</p> Signup and view all the answers

    What is a significant consequence of spores produced near the end of the growing season?

    <p>Infection of collar leading to collar rot</p> Signup and view all the answers

    What is one cultural strategy recommended for managing rice blast disease?

    <p>Maintaining flood levels in rice fields</p> Signup and view all the answers

    How can overuse of nitrogen fertilizers affect rice production?

    <p>It increases the level of rice blast without improving yields</p> Signup and view all the answers

    What is the primary challenge when using genetic resistance to control rice blast?

    <p>New races of the pathogen can develop over time</p> Signup and view all the answers

    Which practice is highly recommended to help in the prevention of rice blast disease?

    <p>Prioritizing genetic resistance in rice cultivars</p> Signup and view all the answers

    What happens to rice cultivars containing a single resistance gene over time?

    <p>They may become susceptible to new pathogen races</p> Signup and view all the answers

    Why is crop rotation advised as a strategy to manage rice blast?

    <p>It separates viable spores from new seedlings</p> Signup and view all the answers

    What is the consequence of under-irrigating rice fields?

    <p>It can lead to more severe rice blast outbreaks</p> Signup and view all the answers

    What is one of the key reasons for utilizing high-quality, disease-free seeds in rice cultivation?

    <p>To prevent the transmission of pathogens from the soil</p> Signup and view all the answers

    Study Notes

    Rice Blast Disease

    • Rice blast is a severe plant disease that affects rice (Oryza sativa), a staple food crop for millions globally.
    • The disease is caused by the fungus Magnaporthe oryzae (formerly known as Pyricularia oryzae).

    Symptoms and Signs

    • Rice blast causes lesions on various parts of the rice plant, including leaves, stems, panicles, seeds, and even roots.
    • The most common and diagnostic symptom is diamond-shaped lesions on the leaves.
    • The pathogen produces sexual spores (ascospores) in structures called asci, classifying it as an ascomycete.

    Sexual Reproduction

    • The sexual, or teleomorphic, stage of the pathogen can be produced in the laboratory but has not been observed in the field in the United States.
    • The pathogen exhibits a bipolar mating system controlled by two different alleles at a single locus, with additional genes influencing the sexual cycle.

    Asexual Reproduction

    • The asexual stage of Magnaporthe oryzae is represented by the Pyricularia oryzae form, the most common spore form in the USA.
    • These spores, called conidia, are produced abundantly on lesions and are easily dispersed by wind.

    Infection Process

    • Infection occurs when conidia land on rice tissues and germinate, forming a germ tube and an appressorium.
    • The appressorium, a melanized structure, develops an infection peg that penetrates the tissue, leading to rapid growth within susceptible tissues.

    Disease Cycle & Epidemiology

    • Rice blast thrives in moderate temperatures (24°C) and periods of high moisture, conditions commonly found in flooded rice fields.
    • The overwintering sources of spores include grasses, volunteer plants, infested refuse, and infected seed on the soil surface.
    • The disease severity is linked to the amount of infested material, leading to more severe disease in plots with higher amounts of primary inoculum.

    Disease Management

    • Rice blast management involves a comprehensive approach combining various techniques, including:
      • Cultural strategies:
        • Crop rotation to separate spores from seedlings
        • Proper fertilization to avoid excess nitrogen
        • Maintaining proper flood levels
        • Using high-quality, disease-free seed
      • Genetic resistance:
        • Utilizing rice cultivars with genes conferring resistance to specific races of the fungus
        • The challenge is the emergence of new races that overcome existing resistance genes.

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    Related Documents

    Rice Blast 2007 PDF

    Description

    Explore the critical information about rice blast disease, caused by the fungus Magnaporthe oryzae. This quiz covers symptoms, signs, and the reproductive stages of the pathogen. Test your knowledge on this significant disease affecting rice crops worldwide.

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