Transmission (Dissemination) of Bacteria
The bacterial diseases are mainly disseminated through the agency of seed, air and water.
Xanthomonas campestris pv. oryzae ( in Paddy), X.campestris pv. malvacearum ( in cotton) are carried either externally or internally through seed. Corynebacterium sepedonicum and pseudomonas solanacearum (in sugarcane) are spread through vegetative plant parts used for propagation.
Phytopathogenic bacteria live as saprophytes on plant residues in the soil and when suitable host plants are sown they become active pathogens. They are disseminated from place to place by means of cultivation operations, tool of cultivation and related agencies- human and animal and also through irrigation water, rain water and wind E.g of disease spread: Bacterial blight of cotton ( X. campestris pv. malvacearum).
Bacteria surviving on fallen leaves etc and in soil are carried in the wind for long distance and deposited on the host plants.
4. Rain and Water:
Rain drops falling on bacterial pustules or oozo present on the host surface distribute the bacteria in fine droplets to to other portions of the plant. The motile ones can move short distances in drops of water on plant parts and gain entry into the plant tissues. Rain water especially when accompanied by wind, forms an important agent for rapid spread of the pathogens. Bacteria in soil are carried via rain or irrigation water. E.g of disease spread: leaf blight of rice Xanthomonas campestris pv. oryzae.
Insects play a major role in the dissemination of bacteria. They act as carries of bacterial cells as well as help in infection through wounds E.g disease spread through insects: Fire blight of apple (Erwinia amylovora).
Use of contaminated tools and bags during cultural operations and movement of infective material by implements and other agencies during various field operations also play an important role in the spread of bacterial disease e.g of disease spread : Brown rot of potato (Pseudomonas solanacearum)
Man is the agent behind the long distance dissemination which takes place chiefly through infected seeds and vegetative propagating material. E. g of disease spread: Leaf blight of paddy (Xanthomonas. compestris pv. oryzae), brown rot of potato ( Psudomonas solanacearum).