Survival Mechanisms of Plant

Pathogens

&

Disease Management

Disease Triangle

Source: http://www.finegardening.com/10-ways-keep-your-garden-healthy

Survival mechanisms of pathogens

1. Survival by means of specialized resting structures

2. Survival as saprophytes

3. Survival in vital association with living plants

4. Survival in association with nematodes and fungi

5. Survival in association with insects

6. Survival on agricultural materials

7. Survival on surface water

Survival on agricultural materials

• Some pathogens can survive,

• Inside air dried tissues of diseased plants, establishing an epiphytic population

• as dried slime on machinery or containers.

• e.g. :Clavibacter michiganensis subsp. michiganensis

(causative agent of bacterial wilt and canker of tomato)

• survive in air-dried conditions for 7 to 8 months on the surface of wooden stakes and boxes or wires

• Survive for 15 months in air-dried tissues of diseased tomato plants.

Source: http://bacmap.wishartlab.com/organisms/512

Clavibacter michiganensis subsp. Sepedonicus

(causative agent of potato ring rot)

• survive and remain infectious on potato bags, barn walls, machinery and other equipment.

• Survives inside of an infected tubers

Source: http:// www.pinterest.com/pin/515169644851653467

Disease Management

• Using disinfectants ,such as quaternary ammonia, chlorine, iodine or phenol-containing compounds applied to equipment and other contaminated surfaces.

• Removing or isolating diseased crops debris can be helpful to reduce the rate of infection

• Burial of diseased debris is often useful along with crop rotation

Survival in association with insects

• Facilitate transmission from one host to another

• No harm to the insect act as carriers / vectors

• Lives in a symbiotic relationship

Pathogen protection from adverse weather conditions

Insect supply digestive enzymes

Most of the pathogens do not reproduce inside the vector

e.g.

1) Erwinia amylovora honey bee

Fireblight

2) Pectobacterium & Dickeya sp. Fruit flies

soft rot plant tissues

Some pathogens multiply within the host

e.g.

Pathogen vector

1). Xylella fastidiosa

leaf hopper

2). Ca. liberibacter

psyllid

• Multiply in the gut & the salivary glands.

through wounds

Pathogens Plant

inside the insect due to biting, chewing, piercing

Disease management by controlling theinsect/vectors

Chemical control

• insecticides

• horticultural oils e.g. stylet oil

• insect repellents

Resistant crop varieties

• Resistance that prevents feeding or repels the insects can prevent transmission of pathogens spread by feeding

cultural control

• elimination of weed hosts of vectors

• Adjusting planting dates can minimize crop exposure to vectored pathogens

Survival of plant pathogens on surface water

• Till contact the specific host • Inoculum-Individual itself • Stage of life cycle (E.g.: Vegetative body, Dormant

mycelium, Asexual Spores, Sexual spores ) capable of causing disease

• Vectors

Bacteria1. Erwinia carotovora2. Xanthomonas campestris

Erwinia carotovoraSource: http://www.usu.edu/westcent/microstructure_food/Erwinia.htm

• Viruses Tomato bushy stunt viruszoospores of Olpidium virulentus - vector of the lettuce big vein virus

• FungiPhytophthora species (oospores,zoospores)

Olpidium virulentus (zoospores)

• NematodesIndividuals Ditylenchus hemicycliophoraCysts Heterodera

Olpidium virulentusSource:https://www.paceturf.org/photo/member-galleries/p1585-olpidium.html

Management Of Pathogens

Using Resistant crop varieties Treatment of waste water Treat the water - slow sand filtration ,

using Heat, ultraviolet light, ozone, and chlorination

Improve water drainage Using other varieties of crops Chemotherapy( E.g. fungicides)

FungicidesSource: http://pnwhandbooks.org/plantdisease/pesticide-articles/fungicides-disease-control-home-landscape

Slow Sand filtrationSource: http://greendesert.org/sandfilter.html

Reference:• Hong, X. C. and Moorman, W. G. (2005). Plant Pathogens in Irrigation Water. Challenges and

Opportunities-Critical Reviews in Plant Sciences.24-3: 189-208.

• http://pnwhandbooks.org/plantdisease/pesticide-articles/fungicides-disease-control-home-landscape (18.09.2015)

• http://greendesert.org/sandfilter.html (19.09.2015)

• http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/pythium (19.09.2015)

• http://www.usu.edu/westcent/microstructure_food/Erwinia.htm (19.09.2015)

• https://www.paceturf.org/photo/member-galleries/p1585-olpidium.html (19.09.2015)

• http://www.apsnet.org/edcenter/intropp/pathogengroups/pages/bacteria.aspx • (19.09.2015)

• http://www.eppo.int/QUARANTINE/bacteria/Clavibacter_m_sepedonicus/CORBSE_ds.pdf ( 19.09.2015)

• Gleason,M.L., Barun,E.J., Carlton,W.M. and Peterson,R.H. 1991. Survival and Dissemination of Clavibacter michiganensis subsp.michiganensis in Tomatoes. Journal paper J-14244 of the Iowa Agriculture and Home Economics Experiment Station 81: 1519-1521.

• http://www.finegardening.com/10-ways-keep-your-garden-healthy (19.09.2015).