Gray speck of oats and marsh spots of peas are caused by:

Options

A. Deficiency of Mn
B. Deficiency of Mn and Mo respectively
C. Deficiency of Mo and Mn respectively
D. Excess of Mo

Answer

To solve the question regarding the cause of gray speck of oats and marsh spots of peas, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Diseases**: The question mentions two specific conditions: gray speck of oats and marsh spots of peas. We need to determine the cause of these conditions.

2. **Research the Causes**: Gray speck of oats is known to be associated with certain nutrient deficiencies. Specifically, it is linked to the deficiency of manganese.

3. **Understand the Symptoms**: The symptoms of gray speck disease include the appearance of irregular and brownish lesions on the leaves of the affected plants. This indicates that the plant is suffering from a nutrient deficiency.

4. **Consider Other Nutrient Deficiencies**: The question also mentions marsh spots of peas. This condition can also be related to nutrient deficiencies, particularly molybdenum. However, the primary cause of gray speck is manganese deficiency.

5. **Eliminate Incorrect Options**:
- The deficiency of molybdenum leads to stunted growth due to the accumulation of nitrates, which is not the cause of gray speck.
- The presence of excess molybdenum can lead to a condition known as molybdenosis, which is also unrelated to the gray speck disease.

6. **Conclude the Correct Answer**: Based on the information gathered, the gray speck of oats and marsh spots of peas are primarily caused by the deficiency of manganese.

### Final Answer:
The gray speck of oats and marsh spots of peas are caused by the deficiency of manganese.

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