Question

Choose the correct statements regarding Nonhost resistance (NHR) and Host resistance in plants:
A. Type I Nonhost resistance does not have visible symptoms
B. Type II Nonhost resistance is always associated with hypersensitive reaction
C. Neither Type I nor Type II Nonhost resistance is useful for resistance breeding
D. Type II Nonhost resistance and Host resistance involve the same signal transduction pathway
E. Only Type I Nonhost resistance is useful for resistance breeding

• A. C and E only
• B. A and C only
• C. D and E only
• D. A, B and D only

Hint:

Remember the core difference:
- Type I NHR = No visible symptoms (early-stage arrest).
- Type II NHR = Visible symptoms, primarily Hypersensitive Response (HR) localized cell death (late-stage arrest).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Nonhost resistance (NHR) is the most common form of disease resistance exhibited by an entire plant species against all isolates of a specific pathogen species.
NHR is broadly categorized into two types based on the cellular response and presence of visible symptoms.
Detailed Explanation:
Let us analyze each statement:
Statement A is correct:
Type I Nonhost resistance does not result in any visible symptoms on the host.
The pathogen is arrested at an early stage, such as during pre-invasion or pre-haustorial stages, without triggering cell death.
Statement B is correct:
Type II Nonhost resistance is characterized by a hypersensitive response (HR) resulting in localized cell death.
The pathogen is recognized post-invasion, triggering rapid programmed cell death to restrict pathogen progress.
Statement C is incorrect:
Both Type I and Type II NHR are highly durable and represent extremely valuable targets for transgenic and molecular plant breeding programs to engineer broad-spectrum disease resistance.
Statement D is correct:
Type II NHR and host-specific resistance (often mediated by R-genes) rely on overlapping immune receptors and signal transduction pathways.
These include the activation of salicylic acid pathways, reactive oxygen species generation, and MAPK cascades.
Statement E is incorrect:
Both forms of NHR can be exploited for crop improvement, not just Type I.

Step 2: Final Answer:
Statements A, B, and D are scientifically accurate.
Therefore, the correct option is (D).