Text for UF/IFAS/Plant Pathology “Plant Pathogen Groups” PowerPoint

Slide / Text: The text below is supplementary to what is presented on the slide itself
1 / Topics that will be discussed in this powerpoint.
2 / Abiotic plant problems are not caused by plant pathogens, but rather are caused by environmental factors, either natural or man-made.
3 / This is no different than with human problems. Many times what we refer to as human diseases have no pathogen causing the “disease”. These are a few examples of human problems that would be considered “abiotic”.
4 / It is extremely important to know, especially when trying to diagnose the plant problem, that both biotic and abiotic problems can affect the plant at the same time. Sometimes they are interacting with each other, but at other times, they are completely independent of each other.
5 / The photos of the palm trees are examples of lightning strikes directly to the trees. Palms are often the tallest element in the landscape, and they contain more water than hardwood trees. This is why we believe they are often hit by lightning. Our beloved pet dog often damages Turfgrass when they urinate. But, we still love them!
6 / We love our tropical plants, like bananas, but they are not always well-adapted to our southern temperate or sub-tropical climates in Florida. In some situations, it is not the actual temperature that is so damaging, but the sudden, quick drop in temperature.
7 / Sunburned palm leaflets and a sunburned red pepper fruit.
8 / A common problem of orchids and other fleshy-leaves plants is oedema. “Water, water everywhere” is not usually conducive for plant growth.
9 / Just as too much water can be problematic, so can too little water. Wilting plants is a common symptom of drought, but leaf necrosis (dead tissue) is an even better indicator of drought stress.
10 / Six examples of nutrient deficiency symptoms. Some plants, such as palm trees, are more likely to die from nutrient deficiencies than from diseases, and often the nutrient deficiency is due to improper fertilization.
11 / It is not only herbicides than can damage plants, improper use of fertilizers can cause problems also.
12 / Diseases are biotic plant problems, as there is a second organism (and sometimes 2 or 3) that are infecting the plant and disrupting its normal appearance and growth.
13 / A major concept in plant pathology is referred to as the Plant Disease Triangle. It has been expanded upon, but it still helps to explain why diseases occur. The idea is that a specific disease will not occur unless the susceptible host and the pathogen are interacting within a favorable environment.
14 / A crude drawing to illustrate the Plant Disease Triangle. The point is that only when all 3 components of a disease overlap does disease develop.
15 / This slide illustrates that if all 3 components of a disease do NOT overlap, disease does NOT occur. We will bring in the vector component of some plant pathogens later in the workshop. For now, we will keep it simple.
16 / This is the list of plant pathogens – a wide variety of sizes and lifestyles!
17 / First, we will discuss fungi and Oomycetes. As scientists learn more about an organisms, we reclassify what kingdom it belongs to and expand the number of kingdoms representing life.
18 / Fungi and oomycetes represent many lifestyles. These are the major ones pertinent to plant pathology.
19 / This chart illustrates the differences between oomycote and the “true” fungi. If you want to learn more about these differences, links are provided in the slide.


20 / These are cool videos of zoospores, which are unique to Oomycota. The top one is 55 seconds. The bottom one is 90 seconds (cool music with this one, so have sound on if possible).
(55 sec)
(90 sec)
21 / These are the diseases caused by some Oomycetes.
22 / Fun fungal factoids. While fungi are highly abundant on earth and are the major cause of plant diseases, there are only a few fungi that are known to cause plant diseases.
23 / More fun fungal factoids. Again, not all fungi associated with plants are pathogens.
24 / Endophyte example, which like many relationships, can be good for one organism, but bad for another. Two examples of beneficial fungal symbiosis.
25 / These are the main fungal groups – not all contain plant pathogens. For example, the arbuscular mycorrhizae of the Glomeromycota are not pathogens.

26 / These are the four fungal phyla that contain plant pathogens.
27 / Most plant pathogens are in the Ascomycota phyla. Sex and the Fungi! It can become very confusing when we start talking about fungal names in the Ascomycota. In the past, we often used one name for the asexual state and an entirely different one for the sexual state.
28 / Sordaria is not a plant pathogen, but these photos are good illustrations of 8 ascospores in the ascus (bottom photo), with the asci (plural for ascus) emerging from the ascocarp. The photos on the right illustrate ascospores within asci (top photo) and individual ascospores of the palm fungus Serenomyces.
29 / These are examples of conidia (asexual spores) of different fungal species. All different shapes and sizes, with and without appendages. Pestalotiopsisconidia have3 appendages at one end and a short, single one at the opposite end. Lasiodiplodia conidia start as hyaline (colorless), single-cell structures, but as they age, they darken and become 2-celled structures. Exserohilum produces large, cigar-shaped conidia. Some Phomopsis species produce these boomerang-like conidia. Most Fusarium oxysporum pathogens produce two different types of conidia – macroconidia (the larger one) and microconidia (the smaller ones). Cylindrocladium produces a very uniform 2-celled, hyaline spore with nice rounded ends.
30 / The Basidiomycota phyla of true fungi primarily contains rust fungi, smut fungi and fungi that rot wood. The rust fungi are very interesting. They have a multi-spore life cycle and can have a multi-host life cycle. These are some of the most devastating diseases worldwide and control has normally relied on breeding for resistance.

31 / We have already been introduced to the smuts.
32 / Most, but not all, wood decay fungi that are plant pathogens are in the Basidiomycota phylum. These are two examples of wood decay pathogens that commonly occur in Florida.
33 / There are not very many Chytridiomycota fungi that are associated with plant diseases, but all are obligate fungi (they need the plant host for survival). This is an example of two chytrids – one which causes a disease of potato and one which transmits (vectors) a virus that causes a disease of lettuce.
34 / Bacteria cause diseases of plants, but not nearly as many diseases as fungi and viruses.

35 / There are a special group of bacteria, fastidious bacteria, that are especially important in Florida. One group are called phytoplasmas, which do not have cell walls. Lethal yellowing and Texas Phoenix Decline of palms are caused by phytoplasmas. Citrus greening (Huanglongbing) is caused by a fastidious bacterium. All of these fastidious bacteria are moved from plant to plant by an insect vector.

36 / These are photos of a phytoplasma, spiroplasma and Xylella.
37 / Viruses are unique and one discussion that you can have with students starts with the question: Are viruses living organisms? What do you think?


38 / Illustration of the size difference of virus particles. The one on the left has a size bar of 75 nm. The size bar for the photo on the right is 500 nm.
39 / All viruses are spread by movement – either passive or active. Most are moved by arthropods. Since mites are one vector, we technically can’t state “insects”.
40 / An even smaller “organism” that causes plant diseases is a viroid.

41 / Size is not important when causing a disease. Even viroids cause devastating diseases.
42 / Nematodes are multicellular animals, but we do include them as plant pathogens.


43 / Characteristics of plant parasitic nematodes. An endoparasitic nematode does live within the plant cell for part of its life, whereas an ectoparasitic lives on the outside of the plant and simply attacks from the outside. Nematodes not only attack roots, but they can occur on above ground plant parts too. Florida is ideal for nematodes as they need water to survive.
44 / Which Plant Pathogen Are YOU?
45 / Now, it is time to answer that question. This personality test was developed by APS, but adapted from the ASM personality test. There are a series of questions to answer that will lead you to a number which corresponds to a pathogen and the disease(s) that it causes.

46 / There is a “card” for each pathogen/disease. For most, but not all pathogens and diseases, next to the credit for the photo (bottom left corner), there is a letter + number listed. This corresponds to a publication about the pathogen/disease in the UF/IFAS Electronic Data Information System (EDIS). When you go to the EDIS home page ( , type in the letter/number in the search box.
47 / There are 30 cards representing 30 pathogens/diseases. Again, most, but not all, will have an EDIS document, which means that the disease does occur in Florida or has the strong possibility of occurring in Florida. Others are very common or very important diseases elsewhere in the world, but not in Florida. For example, coffee rust is included, as some of us in our coffee every day!
EDIS publications are reviewed at least every 3 years to keep the information as current as possible. They are written by the experts in their field of science. You are very welcome to use the information and the photos in EDIS documents, but please acknowledge where the information and photos are obtained.
48 / Now, which plant pathogen are YOU!

Text for Plant Pathology PowerPoint “Plant Pathogen Groups”, Page 1