Model Answer
0 min readIntroduction
Plant diseases pose a significant threat to global food security, causing substantial yield losses in agriculture. Crucifers (like cabbage, cauliflower, and mustard) and sugarcane are economically important crops, and their susceptibility to diseases like white rust and red rot, respectively, can have devastating consequences. White rust, caused by *Albugo candida*, is a widespread disease affecting cruciferous plants, while red rot, caused by *Colletotrichum falcatum*, is a major constraint in sugarcane production. Understanding the symptoms, causal organisms, and control measures for these diseases is crucial for effective crop management and ensuring sustainable agricultural practices.
White Rust of Crucifers
White rust, caused by the oomycete fungus *Albugo candida*, is a serious disease affecting cruciferous vegetables and oilseed crops. It is characterized by the formation of white, powdery pustules on the undersurface of leaves.
Symptoms
- Early Stage: Small, chlorotic (yellowish) spots appear on the upper surface of leaves.
- Advanced Stage: Corresponding to these spots, white, blister-like pustules develop on the underside of the leaves. These pustules are initially small but enlarge and coalesce, covering large areas.
- Severe Infection: Leaves become distorted, brittle, and may eventually die. The disease can also affect stems and flower stalks.
- Systemic Infection: In severe cases, the fungus can invade the vascular system, leading to systemic symptoms.
Causal Organism
*Albugo candida* is an obligate parasite, meaning it can only survive and reproduce on living host plants. It produces zoospores, motile spores that spread the disease through water splashes.
Control Measures
- Resistant Varieties: Using resistant varieties is the most effective control measure.
- Seed Treatment: Treating seeds with fungicides like tricyclazole or metalaxyl.
- Crop Rotation: Rotating cruciferous crops with non-host plants.
- Sanitation: Removing and destroying infected plant debris.
- Fungicides: Application of systemic fungicides like tricyclazole or metalaxyl during early stages of infection.
- Biological Control: Utilizing bio-control agents like *Trichoderma* species.
Red Rot of Sugarcane
Red rot, caused by the fungus *Colletotrichum falcatum*, is a widespread and destructive disease of sugarcane, causing significant yield losses. It affects all parts of the plant, including the setts (seed pieces), stalks, and leaves.
Symptoms
- Sett Back: Reddish-brown discoloration of the setts before planting, leading to poor germination.
- Early Stage (Stalks): Reddish-brown streaks appear on the outer surface of the stalks, often starting from the nodes.
- Advanced Stage: The streaks deepen and become sunken. The internal tissues of the stalk become reddish-brown and hollow.
- Leaf Symptoms: Reddish-brown lesions appear on the leaves, often with a yellow halo.
- Top Rot: In severe cases, the top of the sugarcane plant may rot, leading to stunted growth and reduced sugar content.
Causal Organism
*Colletotrichum falcatum* is a hemibiotrophic fungus, initially behaving as a biotroph (obtaining nutrients from living host cells) and later becoming a necrotroph (feeding on dead tissues). It produces conidia, asexual spores, which are spread by wind, rain, and infected setts.
Control Measures
- Disease-Free Setts: Using setts from healthy, disease-free plants.
- Sett Treatment: Treating setts with fungicides like carbendazim or propiconazole.
- Crop Rotation: Rotating sugarcane with non-host crops like rice or wheat.
- Sanitation: Removing and destroying infected stalks and plant debris.
- Resistant Varieties: Cultivating sugarcane varieties resistant to red rot.
- Biological Control: Utilizing bio-control agents like *Trichoderma* species and *Pseudomonas fluorescens*.
- Balanced Fertilization: Providing balanced nutrition to enhance plant vigor and resistance.
Comparative Table: White Rust vs. Red Rot
| Feature | White Rust (Crucifers) | Red Rot (Sugarcane) |
|---|---|---|
| Causal Organism | *Albugo candida* (Oomycete) | *Colletotrichum falcatum* (Ascomycete) |
| Affected Plant Parts | Leaves, stems, flower stalks | Setts, stalks, leaves, top of plant |
| Primary Symptoms | White, powdery pustules on underside of leaves | Reddish-brown streaks on stalks, hollow stalks |
| Spore Type | Zoospores | Conidia |
| Mode of Spread | Water splashes | Wind, rain, infected setts |
Conclusion
Both white rust of crucifers and red rot of sugarcane represent significant challenges to agricultural productivity. Effective management strategies rely on a combination of preventative measures, including the use of resistant varieties, disease-free planting material, and appropriate sanitation practices. Integrated disease management approaches, incorporating biological control agents and judicious use of fungicides, are crucial for minimizing yield losses and ensuring sustainable crop production. Continuous monitoring and research are essential to develop new and improved control strategies in response to evolving pathogen populations.
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.