a) Wind:

• The dispersal of pathogens by wind is known as anemochory.
• Wind acts as a potent carrier of propagules of fungi, bacteria and viruses.

Fungi:

• Usually the fungal pathogens are light in weight and are well adapted to wind dispersal.

• Ex: Powdery mildew, downy mildew, rusts, smuts etc.

Both short and long distance dissemination is possible by means of wind.

i) Spores adopted for short distance dissemination- sporangia of downy mildew fungi, conidia of powdery mildew fungi and basidiospores of rust fungi.

ii) Spores adapted to long distance dispersal –uredospores of rust fungi Chlamydospores of smut fungi and conidia of Alternaria, Helminthosporium and Pyricularia.

Dispersal distance:

• If the uredospores reach an altitude of 5000 feet, their distance dispersal in a 30 mile per hour wind could be about 1100 miles, without loosing viability.

Nematodes:

• Ex: Cysts of the nematode Heterodera major, which causes molya disease of wheat and barley, are carried by dust storms from Rajasthan to Haryana

Bacteria:

• Some pathogenic bacteria are carried along with the infected material to short distances by wind.
• Ex: Erwinia amylovora, the causal agent of fire blight of apple and pear, produces fine strands of dried bacterial exudates which may be broken off and are transmitted by wind.

Viruses and phytoplasmas are not directly transmitted by wind, but the insect and mite vectors that carry the viruses move to different directions and distances based on the direction and speed of the air.

b) Water:

• Transmission of plant pathogens by water is called as hydrochory.
• Water dissemination occurs mainly through surface running water and rain splash.
• The mycelial fragments, spores or sclerotia of fungi, Colletotrichum falcatum (red rot of sugaecane), Fusarium, Ganoderma, Macrophomina, Pythium, Phytophthora, Sclerotium, etc., are transmitted through rain or irrigation water.
• Dissemination by rain splash is also called as splash dispersal.
• Ex: Bacterial leaf spot of rice (Xanthomonas campestris pv. oryzae), Bacterial leaf streak of rice (Xanthomonas campestris pv. oryzicola), Green ear of bajra (Sclerospora graminicola).
• Water not only plays an important role in the dissemination of plant pathogens, but also helps in the growth and spore discharge of many fungi.