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UPSC MainsBOTANY-PAPER-I201650 Marks
Q15.

Give the name of the causal organism, symptoms and control measures of any four important crop diseases caused respectively by a mycoplasma

How to Approach

This question requires a detailed understanding of plant pathology, specifically focusing on diseases caused by mycoplasmas. The answer should systematically address each part of the question – causal organism, symptoms, and control measures – for four different crop diseases. A tabular format will be highly effective for organizing the information. Focus on providing specific details about each disease, including the scientific name of the mycoplasma involved. The answer should demonstrate knowledge of agricultural practices and disease management strategies.

Model Answer

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Introduction

Mycoplasmas are wall-less bacteria belonging to the class Mollicutes, and are significant plant pathogens causing a wide range of diseases in various crops globally. These diseases are often characterized by yellowing, stunting, and phyllody (flower-like growth of leaves). Their small size and lack of a cell wall make them difficult to culture and identify, leading to significant economic losses in agriculture. Understanding the causal organisms, recognizing the symptoms, and implementing effective control measures are crucial for mitigating the impact of these diseases on crop production. This answer will detail four important crop diseases caused by mycoplasmas, outlining their characteristics and management strategies.

Mycoplasma-Caused Crop Diseases: A Detailed Overview

The following table summarizes four important crop diseases caused by mycoplasmas, detailing their causal organisms, symptoms, and control measures.

Disease Causal Organism Symptoms Control Measures
Little Leaf of Brinjal Phytoplasma auburnense
  • Excessive vegetative growth with small, yellowed leaves.
  • Stunted plant growth and reduced fruit set.
  • Phyllody – floral parts transform into leaf-like structures.
  • Premature flower drop.
  • Removal and destruction of infected plants.
  • Control of leafhopper vectors (Nephotettix spp.) using insecticides.
  • Use of disease-free seedlings.
  • Crop rotation.
  • Yellow sticky traps to monitor and control vector populations.
Sandy Shoot of Sugarcane Phytoplasma saccharum
  • Yellowing and drying of shoot tips, giving a ‘sandy’ appearance.
  • Stunted growth and reduced cane yield.
  • Proliferation of tillers.
  • Internal discoloration of the cane.
  • Use of disease-free planting material (setts).
  • Control of leafhopper vectors (Pyrilla perpusilla) through biological control (Encarsia insignis) and insecticides.
  • Ratooning should be avoided in severely affected fields.
  • Removal and destruction of infected clumps.
Witch’s Broom of Lemon Candidatus Phytoplasma citri
  • Excessive proliferation of shoots, forming a broom-like appearance.
  • Yellowing and distortion of leaves.
  • Reduced fruit size and quality.
  • Decline in tree vigor.
  • Pruning and removal of infected branches.
  • Control of psyllid vectors (Diaphorina citri) using insecticides and biological control agents.
  • Use of certified disease-free planting material.
  • Application of systemic insecticides.
Aster Yellows of Sunflower Phytoplasma asteris
  • Yellowing and distortion of leaves, particularly the upper ones.
  • Stunting of plant growth.
  • Phyllody – flower parts transform into leaf-like structures.
  • Reduced seed set and yield.
  • Control of leafhopper vectors (Macrosteles fascifrons) using insecticides.
  • Use of resistant sunflower varieties (where available).
  • Removal and destruction of infected plants.
  • Early sowing to avoid peak vector populations.

Understanding Mycoplasma Transmission

Mycoplasmas are primarily transmitted by phloem-feeding insect vectors, such as leafhoppers, planthoppers, and psyllids. These insects acquire the mycoplasma from infected plants and transmit it to healthy plants during feeding. The efficiency of transmission depends on factors such as vector species, mycoplasma strain, and environmental conditions.

Challenges in Disease Management

Managing mycoplasma diseases is challenging due to several factors. The lack of a cell wall makes mycoplasmas resistant to many conventional antibiotics. Furthermore, the systemic nature of the infection means that symptoms may not be apparent until the disease is well established. Accurate diagnosis is also difficult due to the slow growth rate and small size of these organisms.

Recent Advances in Detection and Control

Recent advances in molecular techniques, such as PCR and real-time PCR, have improved the accuracy and speed of mycoplasma detection. Research is also underway to develop resistant crop varieties and to identify effective biological control agents for vector management. Furthermore, understanding the molecular mechanisms of mycoplasma pathogenicity is crucial for developing novel control strategies.

Conclusion

Mycoplasma-caused crop diseases pose a significant threat to agricultural productivity. Effective management requires a comprehensive approach that includes the use of disease-free planting material, vector control, crop rotation, and timely removal of infected plants. Continued research into the biology of these pathogens and the development of new diagnostic and control tools are essential for mitigating their impact on food security. Integrated pest management strategies, combining chemical, biological, and cultural control methods, offer the most sustainable solution for managing these challenging diseases.

Answer Length

This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.

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Additional Resources

Key Definitions

Phyllody
Phyllody is a plant disease where floral parts are modified into leaf-like structures. It is a common symptom of mycoplasma infections, resulting in reduced or absent flower formation and seed set.
Phloem-limited bacteria
Mycoplasmas are classified as phloem-limited bacteria because they primarily reside and multiply within the phloem tissues of plants, disrupting nutrient transport and causing various disease symptoms.

Key Statistics

Globally, crop losses due to plant diseases, including those caused by mycoplasmas, are estimated to be around 40% annually, impacting food security and economic stability.

Source: FAO, 2019 (Knowledge Cutoff: 2021)

Studies indicate that the economic losses due to Aster Yellows in sunflower can range from 10% to 50% depending on the severity of the infection and the region.

Source: American Phytopathological Society, 2017 (Knowledge Cutoff: 2021)

Examples

Little Leaf of Brinjal in India

Little Leaf of Brinjal is a widespread disease in India, causing significant yield losses in brinjal cultivation. The disease is particularly prevalent in regions with high leafhopper populations and warm, humid climates.

Frequently Asked Questions

▶Can mycoplasma diseases be cured?

Currently, there is no known cure for mycoplasma diseases in plants. Management strategies focus on preventing the spread of the disease and minimizing its impact through vector control and the use of disease-free planting material.

Topics Covered

BotanyAgriculturePlant diseasesMycoplasmaCrop protection
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