Crop Diseases | Agriculture Optional Notes for UPSC PDF Download

Introduction

Crop diseases, which can negatively impact the yield, growth, and long-term viability of crops, can be caused by various microorganisms such as bacteria and fungi. It is essential to identify and address these diseases in field and horticultural crops through specific management measures.

The field of plant/crop pathology is dedicated to the study of plant/crop diseases. Crop pathology involves the examination and classification of pathogens responsible for these diseases, as well as the understanding of disease cycles. It is vital in the identification and management of diseases affecting field and horticultural crops, including well-known examples like powdery mildew and late blight in potatoes.

Crop Diseases

Crop diseases are conditions that affect crops, leading to reduced yield or changes in their appearance. A crop is considered diseased when it exhibits deviations from its normal physiological processes.

Causative Agents: Crop diseases are caused by various agents, including fungi, bacteria, viruses, mycoplasma, viroids, nematodes, and parasitic flowering plants.

Classification of Crop Diseases:

• Based on the Causative Agent:
  • Infectious diseases are caused by microorganisms like fungi, bacteria, viruses, nematodes, and parasitic plants. These agents can reproduce within or on the host and spread rapidly.
  • Non-infectious diseases result from unfavorable environmental conditions, such as extreme temperatures or abnormal mineral concentrations.
• Based on Occurrence and Geographic Distribution:
  • Endemic diseases are consistently present in a particular region, like wart disease in potatoes.
  • Epidemic diseases spread rapidly to a larger proportion of hosts in a given region within a short time, such as rust.
  • Sporadic diseases occur irregularly and in small numbers, like leaf blight and wilt.
• Based on Infection Level:
  • Localized diseases affect specific parts of the crop.
  • Systemic diseases spread throughout the entire crop, affecting various stages of its life cycle.
• Based on Pathogen Generation:
  • Monocyclic diseases, also known as simple interest diseases, occur in a single generation within one crop season, such as loose smut in wheat.
  • Polycyclic diseases, or compound interest diseases, appear in more than one generation during a crop season, for example, late blight in potatoes.
  • Polyetic diseases are polycyclic diseases that recur over multiple crop seasons, completing their disease cycle in one or more years, like apple cedar rust.
• Based on Symptoms:
  • Smuts diseases are often caused by fungi, like loose smut in wheat caused by Ustilago nuda tritici.
  • Rots diseases affect the underground parts of plants and can be caused by bacteria, fungi, or nematodes.
  • Leaf spot diseases, such as those in wheat, are commonly caused by bacteria like Xanthomonas campestris.
  • Powdery mildew diseases, like the one affecting wheat, can damage stems, flowers, and fruits, as seen in grapes and cucumbers.

Diseases of Field and Horticultural Crops and Their Management

Here are various diseases that affect field and horticultural crops, along with the preferred and widely accepted methods for their management:

• Greening by phloem-limited bacteria (Liberobacter asiaticum) in citrus fruits:
  • This disease can be controlled through the use of pesticides.
• Powdery mildew, caused by Oidium mangiferae (also known as Acrosporum mangiferae):
  • Dusting the affected plants with sulfur is an effective method for managing this common field and horticultural crop disease.
  • High humidity is a significant factor contributing to its prevalence.
• Moko disease, caused by Pseudomonas solanacearum or Burkholderia solanacearum in bananas:
  • Management involves removing infected plants and exposing the soil to sunlight to control the disease.

Crop diseases caused by Nematodes: Nematodes are unsegmented roundworms that often thrive in soil and target the small roots of plants. Some nematode species also feed on buds, stems, leaves, or flowers. Plant-parasitic nematodes obtain their nutrition by extracting plant juices.

Prevention: To prevent crop diseases, it is essential to identify the host plant, distinguish between biotic (living organisms) and abiotic (non-living factors) causes of diseases, and regularly inspect crops for symptoms and signs.

Conclusion

Diseases in plants have the potential to negatively affect their yield, growth, and long-term viability. Therefore, it is vital to diagnose the disease, identify the causative pathogen, and implement effective measures for disease control and management to maintain crop health. The symptoms observed on the plant's surface are key indicators for recognizing and addressing the disease.