The organisms that cause these symptoms include fungi, bacteria, nematodes and viruses. Fungi reproduce mainly by means of spores. Bacteria are microscopic, single-celled organisms. They cause diseases such as galls, leaf spots, soft rots, scabs and systemic disorders. Bacteria are a significant cause of plant disease, because they can multiply very rapidly when proper environmental conditions are present.
Bacteria are as damaging to plant propagation operations as are fungi.
C. Nematodes are very small round worms, usually invisible to the naked eye. They cause galls on roots, root lesions, injure root tips and sometimes cause excessive root branching. They reproduce by eggs. D. Viruses are pathogenic particles that infect most higher plants and animals. Virus can multiply only in living cells.