The correct answer is Option 4: 1, 2 and 3.

Viruses are infectious agents that can replicate only inside the cells of a host organism. They can infect a wide range of hosts, including bacteria, fungi, and plants.

1. Bacteria: Viruses that infect bacteria are called bacteriophages or simply phages. Bacteriophages are the most abundant viruses on Earth and play a crucial role in regulating bacterial populations in various ecosystems. They have a specific host range and can infect and replicate within a particular type or species of bacteria. Bacteriophages are widely used in research and biotechnology applications, including in the development of antibiotics and genetic engineering.

2. Fungi: Viruses that infect fungi are known as mycoviruses. Mycoviruses are found in various fungal species, including those that cause plant diseases, and can affect fungal growth, reproduction, and virulence. Some mycoviruses can also be beneficial to their fungal hosts by providing them with a competitive advantage over other fungi, or by inducing changes that promote symbiotic relationships with other organisms.

3. Plants: Viruses that infect plants are called plant viruses. Plant viruses are responsible for a wide range of diseases in crops, which can result in significant economic losses in agriculture. Plant viruses can be transmitted by insects, nematodes, or through infected seeds, soil, or plant debris. They can cause symptoms such as stunted growth, yellowing, necrosis, mosaic patterns on leaves, and reduced crop yield. Plant viruses pose a major challenge to global food security and require various management strategies, including crop rotation, use of virus-free planting materials, and vector control.

In conclusion, viruses can infect not only bacteria but also fungi and plants. This makes Option 4: 1, 2 and 3 the correct answer. It is important to understand the wide host range of viruses and their impact on different organisms to effectively manage viral infections in various fields such as agriculture, medicine, and biotechnology.