Nematodes, microscopic roundworms, are also responsible for plant damage. Bacterial Pathogens Bacterial pathogens are single-celled organisms that require warmth and moisture to survive and reproduce. Bacteria are not capable of penetrating host plants and enter through wounds or natural plant openings. Bacterial pathogens can enter host plants through splashed water, insects, contaminated tools and equipment, or contact with diseased plants.
Symptoms associated with bacteria include leaf spots, soft rots, scabs, wilts, and galls.
Fungal Pathogens Fungal pathogens can grow on living or dead host plants. Many fungi are able to penetrate host tissue using enzymes. Fungi grow wherever environmental conditions are favorable. Fungi reproduce by producing spores that can be either sexual or asexual in nature. Many fungi require high humidity or free water for germination of spores.