ETIOLOGY OF PLANT DISEASES

ETIOLOGY OF DISEASE Study of causation or origination Study of causation or origination -Greek word “aitiolologia” -Greek word “aitiolologia” means “giving reason for” or “cause’ Sum of all factors contributing Sum of all factors contributing to the occurrence of disease 1.Susceptibility of Host 2.Pathogen 3.Favorable Environment Pathogen Susceptible Host DISEASE Environment

TYPES OF PLANT DISEASE

1. ABIOTIC PLANT PROBLEMS

ABIOTIC PLANT DISEASES Abiotic plant problems are caused by environmental factors, either natural or man-made non-infectious, non-living (abiotic = without life) Abiotic plant problems are caused by environmental factors, either natural or man-made non-infectious, non-living (abiotic = without life) 1.Nutrient imbalances 2.Water availability 3.Temperature extremes 4.Light extremes 5.Chemical toxicity 6.Physical injuries 5

1. NUTRIENT IMBALANCES Often nutrient abnormalities show up as discoloration of foliage Often nutrient abnormalities show up as discoloration of foliage Common discoloration symptoms include: Common discoloration symptoms include: Yellowing Yellowing Chlorosis Chlorosis Necrosis

2. WATER AVAILABILITY Both water deficiency and excess can cause injury to plants short-lived (acute; several hours) or long-lived (chronic; days or weeks) May recover from short-term injury,

3. TEMPERATURE EXTREMES Excessively high or low temperatures can be detrimental to plants. The injury and severity sustained by plants depends on plant species or age, the duration of the temperature event, the time of year, or the interaction with other stresses.

4. LIGHT EXTREMES High light intensity is usually not a problem but low light conditions, High light intensity is usually not a problem but low light conditions, especially for indoor plants, lead to etiolation (tissue are yellowish) Pale color, small leaves and poor growth in addition to failure to flower and long, thin stems Yellowing of new foliage or the lower plant leaves Too much light can sicken or kill plants and affect flowering

5. CHEMICAL TOXICITY Also called phytotoxicity. Also called phytotoxicity. It includes application of 1. 1.Herbicides, cause root stunting or swelling, necrotic spots 2.curling and cupping 2.Insecticides, causes curling and cupping 3. 3.Fungicides, causes bronzing and other symptoms 4. 4.Plant-growth regulators, cause temporary chlorosis in ornamentals 5. 5.De-icing salts, cause burn and chlorosis symptom of leaf blades, 6. 6.Air pollution, cause bronzing, chlorosis and necrosis and cause stunting and distortion

6. PHYSICAL INJURIES Symptoms of broken limbs, flattened tree tops or torn bark on tree trunks are easy indicators of mechanical damage. It includes 1. 1.Storm damage 2. 2.Equipment injury 3. 3.Girdling damage 4. 4.Animal damage

2. BIOTIC PLANT PROBLEMS

BIOTIC PLANT PROBLEMS Biotic plant problems or diseases require a second organism that will infect the plant and disrupt its normal appearance and growth – infectious, living Biotic plant problems or diseases require a second organism that will infect the plant and disrupt its normal appearance and growth – infectious, living 1.Fungi 2.Bacteria 3.Viruses 4.Nematodes 5.Phytoplasmas 6.Parasitic seed plants

1. FUNGI Fungi are the most abundant group of plant pathogens. Fungi are the most abundant group of plant pathogens. Powdery mildew is one example of a disease in which fungal mycelia is visible. Powdery mildew is one example of a disease in which fungal mycelia is visible. Common symptoms include Common symptoms include leaf spots, wilts, blights, cankers, fruit rots, and dieback. Fungal diseases including Fungal diseases including 1.Powdery mildew, 2.Damping off 3.Root rot

2. BACTERIA About 200 types of bacteria are known to cause plant diseases. About 200 types of bacteria are known to cause plant diseases. Common symptoms include Common symptoms include leaf spots, blights, cankers, galls, wilt, dieback, and soft rots Common diseases include Common diseases include 1.Bacterial wilt and 2.Fire blight 3.Crown gall

3. VIRUSES Common symptoms include Common symptoms include mottling, mosaic, leaf distortion, stunting, poor fruit set, mosaics and leaf curls and chlorosis Two common viral diseases are Two common viral diseases are 1.Rose rosette and 2.Tomato spotted wilt

4. NEMATODES Common symptoms include Common symptoms include chlorosis, root galls, damaged roots, stunting, dieback, and reduced yields Common plant parasitic nematodes include Common plant parasitic nematodes include 1.Soybean cyst nematode and 2.Foliar nematode

5. PHYTOPLASMAS Phytoplasmas are extremely small bacteria-like plant pathogens Phytoplasmas are extremely small bacteria-like plant pathogens Common symptoms include’ Common symptoms include’ Virescence, Virescence, bushy appearance,bushy and leaf yellowing and abnormal floral organ Common diseases include Common diseases include 1.Aster yellows phytoplasma 2.Little leaf disease

6. PARASITIC SEED PLANTS Lack the ability to produce all of the nutrients or water they require Lack the ability to produce all of the nutrients or water they require Rely on host plants Rely on host plants Common symptoms include Common symptoms include reduced vigor and dieback Most common parasitic plant is Most common parasitic plant is 1.European Mistletoe 2.Dwarf Mistletoe

PLANT DISEASE DIAGNOSIS

Diagnosis-process used for the identifications of problems Diagnosis-process used for the identifications of problems Preliminary considerations Preliminary considerations Know normal appearance of plant Know normal appearance of plant 1.Proper plant identification 2.Recognize healthy plant appearance 21

STEPS FOR PLANT DISEASE DIAGNOSIS

1.Consider the possible agents abiotic or biotic 2.Consult literature resources for diseases 3.Observe patterns 4.Review culture practices 5.Review environmental conditions 8.Check host specificity 9.Check for sign and symptoms 10.Laboratory examine and testing 11.Final diagnosis 12.Develop control recommendations

PRINCIPLES OF PLANT DISEASE CONTROL

Avoidance—prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection. Exclusion—prevent the introduction of inoculum. Eradication—eliminate, destroy, or inactivate the inoculum. Protection—prevent infection by means of a toxicant or some other barrier to infection. Resistance—utilize cultivars that are resistant to or tolerant of infection. Therapy—cure plants that are already infected.