The most well studied bacterial- plant relationship is that of

Options

A. Gall formation on certain angiosperms by Agrobacterium
B. Nodulation of Sesbania stems by nitrogen fixing bacteria
C. Plant growth stimulation by phosphate– solubilising bacteria
D. Cyanobacterial symbiosis with some aquatic ferns

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for the most well-studied bacterial-plant relationship. This indicates we need to identify a specific interaction between bacteria and plants that has been extensively researched.

2. **Evaluating the Options:**
We have several options to consider:
- Gall formation on certain angiosperms by Agrobacterium.
- Nodulation of Sesbania stems by nitrogen-fixing bacteria.
- Growth stimulation by phosphate solubilizing bacteria.
- Cyanobacteria symbiosis with some ferns (e.g., Azolla).

3. **Analyzing Each Option:**
- **Gall formation by Agrobacterium:** This is known to involve Agrobacterium tumefaciens, which causes tumors (galls) in dicot plants through its tumor-inducing (TI) plasmid. This relationship is well-studied and has significant implications in genetic engineering.
- **Nodulation of Sesbania:** While this involves nitrogen-fixing bacteria, it is not as extensively studied as the Agrobacterium relationship.
- **Growth stimulation by phosphate solubilizing bacteria:** This relationship is important but lacks the depth of study compared to Agrobacterium.
- **Cyanobacteria symbiosis with ferns:** This is a notable relationship but does not have the same level of research focus as Agrobacterium.

4. **Identifying the Correct Answer:**
Based on the analysis, the most well-studied bacterial-plant relationship is the gall formation on certain angiosperms by Agrobacterium tumefaciens.

5. **Conclusion:**
Therefore, the answer to the question is: **Gall formation on certain angiosperms by Agrobacterium.**

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