Question

Arrange the stages in the life cycle of "Puccinia graminis" in correct order of their occurrence, starting from Triticum aestivum
A. Teliospores appear as black raised streaks along leaf sheaths and stems of infected plants.
B. Basidiospores are discharged by an explosive mechanism and disseminated by wind.
C. Uredinospores germinate on wheat and spread the disease rapidly, under favorable conditions.
D. Basidiospores germinate on the leaves of the alternate host.
Choose the correct answer from the options given below:

• A. B, A, C, D
• B. D, B, C, A
• C. C, A, B, D
• D. D, B, A, C

Hint:

Remember the host association for {Puccinia} spores: Urediniospores and Teliospores are on the primary host (wheat). Basidiospores infect the alternate host (barberry). Aeciospores (from barberry) infect the primary host (wheat). The red rust (Uredinia) always precedes the black rust (Telia) on wheat.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The question asks to arrange the stages of the life cycle of {Puccinia graminis} (the black stem rust fungus) in the correct order, beginning with the infection on its primary host, wheat ({Triticum aestivum}). This fungus has a complex life cycle involving two hosts (wheat and barberry) and five spore stages.
Step 2: Detailed Explanation:
Let's trace the life cycle starting on wheat:

Stage on Wheat (Summer): The disease first appears on wheat as reddish-brown pustules, which contain urediniospores. These spores are responsible for the repeating stage of the infection, spreading rapidly from one wheat plant to another during the growing season. This matches statement C.

Stage on Wheat (Late Summer/Autumn): As the wheat plant matures, the fungus switches to producing teliospores in the same pustules, which now turn black. These teliospores are the overwintering stage. This matches statement A.

Stage after Overwintering (Spring): In the spring, the diploid teliospores undergo meiosis and germinate to produce a basidium, which bears four haploid basidiospores. These basidiospores are then released. This matches statement B.

Stage on Alternate Host (Barberry): The basidiospores are unable to infect wheat. They are carried by the wind and must land on and infect the alternate host, the barberry plant ({Berberis} sp.). This matches statement D. (On the barberry, the fungus will produce pycniospores and then aeciospores, which will then infect wheat to start the cycle again).
Step 3: Final Answer:
The correct chronological sequence starting from the main disease stage on wheat is C (Urediniospores) \(\rightarrow\) A (Teliospores) \(\rightarrow\) B (Basidiospore discharge) \(\rightarrow\) D (Basidiospore germination on alternate host). This corresponds to option (C).