Transcript CHAPTER 3
CAUSES OF PLANT DISEASES CHAPTER 2 Factors Affecting Abiotic Biotic • Climatic, temperature & other physical factors • Insects, nematodes, mites, fungus, bacteria &virus Abiotic Factors Caused by non living factors such as: Nutritional abnormalities Pesticide exposure Environmental pollutants Extreme weather conditions 1. Nutritional Abnormalities Often nutrient abnormalities show up as discoloration of foliage Common discoloration symptoms include: Yellowing Chlorosis Nutrient Deficiencies Plants require several major (N, P, Ca, Mg) and minor (iron, copper, Zn) elements for normal growth. Deficiency or lack of any of these essential nutrients results in disease symptoms in the plant. The symptoms in this photo occur due to a lack of molybdenum (minor plant nutrient) Mineral Toxicity Presence of excessive available amounts of certain minerals in the soil can lead to mineral toxicity to the plants. The extent of injury depends on the mineral, its concentration, & the species of the plant. The plant in this photo has received too much copper, which has proved toxic and led to yellowing. 2. Pesticide Exposure Some pesticides, if improperly used, can cause serious damage to plants. However, the most common type of chemical injury to plants is due to soil residues or spray drift of herbicides. Examples of pesticide toxicity are: 2,4-D damage to beans and tomatoes glyphosate (Roundup) damage to fruit trees The common symptoms of herbicide exposure are curling and cupping This plant was exposed to the herbicide 2,4-D 3. Environmental Pollutants High levels of fluoride in water or fluorine gas in the air can cause symptoms like this. The damage is concentrated towards the margins of the leaf where fluorine tends to accumulate. Air Pollution Certain chemicals, such as O3, SO2, and NO2 are released into the air from factories, power plants, and automobile exhausts. These chemicals can accumulate in the atmosphere insufficient concentration to cause damage to plants. Ozone damage appears in the form of chlorosis, spots, and bleaching of young leaves. This is common in certain regions of the country where there is a high ozone concentration in smog Some of the air pollutants responsible for acid rain cause damage to vegetation in certain regions. Ozone Damage on Morning Glory Plant Ozone Damage of marijuana leaves 4. Extreme Weather Conditions Extremes of weather can also lead to plant injury Cold injury Low temperatures, like frost or freeze, can damage the exposed or sensitive organs (buds, flowers, young fruits) or may kill the entire plant. As the new branch tips began to expand, a period of cold was severe enough to kill the growing tips Heat injury In this case the temperature was high enough and damage the plant tissue When plants or plant parts are exposed to high temperatures for prolonged periods, symptoms of scorching or scalding may develop High/Low Soil Moisture Due to excessive watering, poor drainage or flooding may cause plants to turn yellow and be stunted. Potted indoor plants may show poor development or root rots. At the other extreme, low moisture or drought conditions can lead to poor development, wilting, and death of plants High/Low Light Intensity High light intensity is usually not a problem but low light conditions, especially for indoor plants, can lead to etiolation (tissue are yellowish) A normal and an etiolated shoot under sun and artificial lighting Biotic Factors Caused by living factors such as : Fungi Bacteria Viruses Nematodes Parasitic Plants 1. Fungi Largest pathogen group More than 8000 pathogenic species Vegetative growth through production of hyphae Reproduce via spores Fungal Hyphae 2. Bacteria About 200 pathogenic species Can be seen with a light microscope Simple, unicellular Reproduce by binary fission 3. Virus Can only be seen using an electron microscope Extremely simple- nucleic acid with a protein coat Reproduce by taking over host reproductive machinery Often associated with insect vectors 4. Nematodes Parasitic worms Very complex compared to other pathogens Usually seen only with a light microscope Reproduce by eggs 5. Phytoplasmas A prokaryotic organism that lack a cell wall and survive in the phloem of plant Round or elongate Usually seen only with an electron microscope Reproduce by binary fission