• Abnormal functioning of an organism.
• A change in the form, functions or physiology of the plant that results in the expression of symptoms.

• Relating to life, as disease caused by living organisms.
  Iinfectious, pathogen, epidemics(epiphytotics; an epidemic in a plant population).

• Pertaining to the absence of life.
• Diseases are not caused by living organisms, but by chemical and physical factors
  Non infectious

• A degree or measure of pathogenicity(ability to cause disease)

• Disease results from an interaction of the virulence of the pathogen, susceptibility of the host and conduciveness of the environment.

• Indication of disease by reaction of the host. ex;cankers, leaf spot, wilt.

• Indication of disease from direct observation of a pathogen or its parts.

• Pathogen or its parts, capable of causing infection when transfered to a favorable location.

• A parasite that typically kills and obtains its energy from dead host cells.

• To make prone to infection and disease.

• An organism that can live and multiply only on another living organism

Biotrophs

• An asexual nonmotile fungal spore that develops externally or is liberated from the cell that formed it.

• A shelf-like, typically hardened basidiocarp of a wood-decaying fungus, usually a polypore(a group of fungi that form fruiting bodies).

• Site in or on a host plant where infection can occur

• Asexual form in the life cycle of a fungus, when asexual spores(such as conidia) or on spores are produced.

• The sexual form in the life cycle of a fungus

• Failure of chlorophyll development, caused by disease or a nutritional disturbance.
• Falding of green plant color to light green, yellow or white.

• Represents the 3 fundamental elements required for disease in plants.

1. a susceptible plant (host)
2. a pathogen capable of causing disease (virulent)
3. a favorable environment (predisposing)

• If any of these 3 elements is missing, no disease occurs

• Conditions which favor plant growth and health commonly favor disease!!

Anthracnose Disease; caused by acervuli-forming fungi and characterized by dark, sunken lesions and necrosis

• Disease of leaves and twigs.
  Produce conidia(spores) in acervuli
• Symptoms; leaf spots, blights, cankers and twig dieback.
  Vein associated symptoms
  Irregular spreading necrotic blotches
  Blight
  Fungi over-summer in dead twigs on the tree.

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Canker disease; a disease characterized(in woody plants) by death of cambium tissue and loss and/or malformation of the bark, or(in woody plants) by the formation of sharply delinated, dry, necrotic, localized lesions on the stem.

• Trees with disease caused by Dothiorella are predisposed by drought in previous yrs.
• Cankers are deep, easily invading the wood.
• Fruiting bodies are very difficult to see because they are covered in dirt.
  There are both pycnidia and perithecia of this fungus present on the cankered branches.
  DNA sequencing is underway at UCR as well as pathogenicity testing.

Vascular Wilt diseases; a xylem disease that disruots normal uptake of water and minerals, resulting in wilting and yellowinf of foliage.

• Symptoms; browning of vascular tissue(xylem)
• One branch death is common.

Rots; softening, discoloration and often disintegration of plant tissue as a result of fungal or bacterial infection.

• Root rots; Armillaria mellea common name Oak root fungus. Signs; mushroom, mycelial fans. Mushroom with an annulus, gills not running down stipe, gregarious and variable in color and size. Symptoms; decline, leaf loss, dieback, basal cankers, bleeding, trunk flat sides and death of the tree.
• Phytophthora spp. various root rots.
  Anoxic conditions; flooding, natural gas leakage.
  Rots caused by water molds, these are actually highly evolved algae, they no longer photosynthesize, bu now parasitize plants. Common in the hort industies and landscapes. Microscopic.

• Results from not one, but many causes
• May involve abiotic and biotic diseases
• Often involves the injurious practices of ppl
• Reduced growth
• Chronic symptoms
• death

• Overwatering and underwatering plants both exacerbate disease.
• Predisposition is the environmental modification of plant resistance making the plant more susceptible to disease.

• A disease-producing organism or agent

Kinds of pathogens; Fungi

• Powdery mildews; ascomycete fungi. A compound interest disease. Obligate biotrohs, overwinter in leaf litter. ASexual conidial stage is Oidium.
• Heart rot; Ganoderma, Laetiporus. Often associated with a decline in vigor. Associated with wounds to roots or the main stem. Wood decay organisms result in wind damage and breakage in trees. Monocyclic didease, the spore enters a wound and invades rays, vessels and fiber coils.

• Plant disease is best manages through an integrated management strategy that includes;

1. cultural practices
2. epidemiology (time for spores to reproduce to intercede and stop the disease)
3. resistant strains (resistance breeding)
4. Chemical pesticides
5. Biological controls (one biological agent against another)

• A major approach to disease control is inoculum reduction.
  Clipping off and disposing of diseased parts, plants or other debris.
  Stopping movement of inoculum; sterilizing clippers, water, soil, etc.
  Stopping vectors od inoculum
  Inhibiting the pathogen from inoculum production.

• Epidemics of introduced (invasive) species are more severe than epidemics od endemic species.
  -Introduction of pathogens is at an all time high in recoded history of the US

Bacterial diseases; Crown gall; soil borne bacteria, infects through wounds, graft unions and can also occur on above ground parts.
-Fireblight; Erwinia amylovora, warm and wet, infects flowers, spread by bees. Infection court floral nectaries. Prune it out
-Bacterial canker; pathogen Pseudomonas syringae. Major disease of all stone fruits. Symptoms, bleeding.
-Bacterial leaf Scortch disease; caused by strains of Xylella fastidiosa vectored by the glassy winged sharpshooter. Symptoms; yellowing, necrosis, total death.

• Quarantine is often the best methos of combating exotic disease.
  -And sometimes the least effective as quarantines are ignored by many including the regulators who institute them.

Nematodes; reduce yield, stuning, loss vigor, wilting, necrosis, death, endoparasitic and ectoparasitic.

• Do no Harm!
  -An understanding of why diseases form and develop gives us a new responsibility to prevent disease through proper horticulture.

Parasitic seed plants; Leafy mistletoe Phoradendron tomentosum.
-Dwarf mistletoe, Arceuthobium

-Dodder

Viral diseases

• Symptoms; vein clearing, mosaics may be vectored by aphids, ringspots, necrosis, stunting, no symptoms.
• Weeds are common viral hosts. Malva as a weed host of lettuce infectious yellow virus.

• Trees in decline undergo a spiraling loss of vigor.
• There are; inciting, sustaining and contributing factors.

• Soil moisture status is the most common predisposing factor to tree declines and disease.
• Drought or overwintering can contribute
• Some fungi (sooty canker) are encouraged by drought.

How do pathogens survive w/o a host?

• Pathogens require survival structures usually spores as they have a thik cell walls, melanization(spores/hyphae/fruiting bodies). Protection within other fungal structures(fruiting bodies).
• Many pathogens lay dormant in the decayed remains of past hosts.

Nematode survival

• Many nematodes survive as fully developed worms inside an egg which may be inside the body or old body(cyst) of the adult female.
• Cryptobiosis; a state of suspended metabolic activity during unfavorable environmental conditions. Survival strategy of some plant pathogenic nematodes.

Fungi survival

• Melanin is the universal protectant for fungi. It cuts down degradation from UV light, it prevents enzymatic degradation of other fungi and slows the loss of water from internal mycelium or spores.
• Biotrophic fungi alternate hosts

• While bacteria do not form structures or exotic spores stages, they can concentrate in Bacterial ooze that can dry down and remain viable for years in old plant materials

• Biotrophic pathogens require a living host and may survive in weeds or suboptimal hosts until they can move over onto a preferred host.

• Leaf surface organisms

• the coordinated development of parasites and their hosts based on degree-days and other environmental factors such that parasites can successfully infect their hosts; eg., the production and release of ascospores of Venturia ineaquilis, the apple scab pathogen, from fallen leaves from previous season, when new apple leaves are expanding

• movement or growth of an organism in response to changing concentration of a chemical stimulus, often in relation to food or for mating.

• Inhibition of fungal growth, sporulation, or spore germination but not death. Used to describe the nonspecific phenomenon in natural soils where spore germination is inhibited, often overcome by rhizosphere nutrients.

• Swollen flattened portion of a fungal filament that adheres to the surface of a higher plant, providing anchorage for invasion by a fungus.
• Infection peg, enzymes

• Abnormal increase in the size of cells in a tissue or organ, often resulting in the formation of galls or tumors.

• Abnormal increase in the number of cells, often resulting in the formation of galls or tumors.

• A molecule produced by the host (or pathogen) that induces a response by the pathogen (or host).

• A site that recognizes and binds an elicitor; any organ or molecular site that is sensitive to a distinct signal molecule

• Unable to cause disease
• Gene in a pathogen that causes the pathogen to elicit an incompatible(defense) response in a resistant host plant and may enhance pathogen virulence in a susceptible host plant. The outcome of the interaction of an avirulence gene product with its corresponding plant resistance(R) gene product is usually a hypersensitive response.

Avirulent

Avirulence (avr) gene

• Gene in bacterial pathogen required for elicitation of the hypersensitive (HR) reponse in resistan plants and causation of disease in susceptible plants; encodes a protein in the type III secretion system.