Model Answer
0 min readIntroduction
Rust fungi, belonging to the order Uredinales, are obligate plant pathogens causing significant economic losses in agriculture. *Puccinia graminis*, the black stem rust of wheat, is a notorious example. The teleutosorus is a crucial structure in the life cycle of these fungi, representing the overwintering stage and facilitating sexual reproduction. It is a specialized sorus containing teleutospores, dikaryotic cells that undergo meiosis to produce basidiospores. Understanding the morphology of the teleutosorus is fundamental to comprehending the disease cycle and developing effective control strategies.
T.S. of Teleutosorus of *Puccinia* – A Detailed Description
The teleutosorus is a dark-colored, often elongated or cylindrical structure formed on the host plant, typically towards the end of the growing season. A transverse section (T.S.) reveals a complex arrangement of cells. The following describes the key features observed in a T.S. of a mature teleutosorus:
1. Structure and Layers
The teleutosorus is embedded within the host tissue and consists of several layers:
- Peridium: The outermost protective layer, formed from host cells, providing a barrier against environmental stresses.
- Teleutospores: The main component, consisting of numerous, dark-colored, thick-walled, binucleate (dikaryotic) cells. These are the overwintering spores.
- Sterigmata: Hyphal branches that support the teleutospores. They arise from the underlying fungal tissue.
- Subhypodermis: A layer of host cells beneath the peridium.
- Mesophyll: The underlying host tissue providing nutrients.
2. Teleutospores – Morphology and Function
Teleutospores are typically dark brown or black due to the presence of melanin in their thick walls. They are generally oval or spherical in shape and possess a prominent pore (germ pore) at one end. This pore facilitates the emergence of the basidium during germination.
3. Basidium Formation and Basidiospores
Upon exposure to favorable conditions (moisture and temperature), the teleutospore germinates, forming a four-celled basidium. Meiosis occurs within the basidium, resulting in the formation of four haploid basidiospores. These basidiospores are forcibly discharged and dispersed by wind, initiating the next stage of the fungal life cycle.
4. Diagram of T.S. of Teleutosorus
Key: 1. Peridium, 2. Teleutospores, 3. Sterigmata, 4. Subhypodermis, 5. Mesophyll
5. Significance in Disease Cycle
The teleutosorus plays a critical role in the completion of the *Puccinia* life cycle. It allows the fungus to survive unfavorable conditions (winter) and undergo sexual reproduction, generating genetic diversity through meiosis. The resulting basidiospores infect alternate hosts, continuing the disease cycle.
Conclusion
The teleutosorus of *Puccinia* is a complex structure essential for the survival and reproduction of rust fungi. Its detailed morphology, including the peridium, teleutospores, and sterigmata, reflects its function in overwintering and initiating the sexual phase of the life cycle. Understanding this structure is crucial for developing effective disease management strategies aimed at disrupting the fungal life cycle and minimizing crop losses. Further research into the genetic mechanisms governing teleospore formation and basidiospore production could lead to novel approaches for rust disease control.
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.