Question

The gene-for-gene relationship between a host and its pathogen was originally proposed by H. H. Flor on the basis of work done on-

• A. Leaf rust of wheat
• B. Late blight of potato
• C. Rust of linseed
• D. Wilt of pigeon pea

Hint:

Always associate:
H.H. Flor $\rightarrow$ Gene-for-Gene Hypothesis $\rightarrow$ Linseed Rust (Melampsora lini).
This is one of the most frequently asked history questions in plant pathology.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The gene-for-gene hypothesis is a fundamental concept in plant pathology.
It states that for each gene conditioning resistance in the host plant, there is a complementary, specific gene conditioning avirulence in the pathogen.

Step 2: Detailed Explanation:
Harold Henry Flor proposed this hypothesis in the 1940s based on his genetic studies of the host-pathogen interaction between flax/linseed (Linum usitatissimum) and flax rust.
The flax rust disease is caused by the biotrophic basidiomycete fungus Melampsora lini.
Flor crossed different host varieties of flax displaying varying levels of resistance, and crossed different physiological races of the rust fungus displaying varying levels of virulence.
By analyzing the F2 segregating generations of both host and pathogen simultaneously, he discovered that:
- Host resistance is typically governed by single dominant genes ($R$).
- Pathogen avirulence is governed by complementary single dominant genes ($Avr$).
This co-evolutionary genetic model remains the foundation of modern molecular plant-microbe interactions.
Options (A), (B), and (D) are incorrect because while they are major host-pathogen systems, they were not the experimental model system used by Flor to formulate his hypothesis.

Step 3: Final Answer:
The gene-for-gene relationship was proposed based on H.H. Flor's work on flax/linseed rust (Melampsora lini).
Therefore, the correct option is (C).