Out of the four options provided, the correct answer is Option 4: 1, 2, 3 and 4. All of these factors can contribute to the spread of plant diseases, either directly or indirectly.

1. Birds: Birds can spread plant diseases by feeding on infected plant material and then depositing the disease-causing agents on healthy plants through their droppings. Some birds, such as sparrows, can also carry fungal spores on their feathers and beaks, which can be transferred to healthy plants upon contact.

2. Dust blowing: Dust blowing can also spread plant diseases indirectly. Dust particles can carry fungal spores or bacteria from infected plants and deposit them on healthy plants. This is especially true in arid regions, where wind erosion is a significant problem.

3. Rain: Rain can also spread plant diseases by splashing infected soil or plant debris onto healthy plants. This is particularly true for fungal diseases that thrive in moist conditions.

4. Wind blowing: Wind blowing can spread plant diseases in a similar way to dust blowing. Wind can carry fungal spores or bacteria from infected plants and deposit them on healthy plants. This is especially true for diseases that affect leaves and stems, as these are the parts of the plant that are most exposed to the wind.

It`s important to note that plant diseases can also be spread through other means, such as insects, contaminated tools, and infected seeds or seedlings. Therefore, it`s crucial to practice good sanitation practices and crop rotation to prevent the spread of plant diseases in agriculture.