Upload
lani
View
72
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Potato Science Lecture 7 Potato diseases – foliar, soilborne , viruses, and tuber rots. . What is plant disease?. Anything that causes disfunction Many (most?) are caused by “infectious biological agents” that are parasitic Others are physiological or “abiotic” (Lecture 15) - PowerPoint PPT Presentation
Citation preview
Potato Science Lecture 7 Potato diseases – foliar, soilborne, viruses, and tuber rots.
What is plant disease? Anything that causes disfunction Many (most?) are caused by “infectious
biological agents” that are parasitic Others are physiological or “abiotic”
(Lecture 15) We will discuss several important
infectious diseases of potato
Causal agents of disease Viruses
Viroids Prions?
BacteriaActinomycetes phytoplasmas fastidious bacteria
Fungi Nematodes
HostPathogen
Environment
Disease Triangle
Disease!
Disease Triangle Plant Pathology is about interactions Host can be altered by choice of variety Use of certified seed reduces pathogen Alter irrigation or drainage changes
environment Usually these factors can’t be
controlled very well Disease is the result
Epidemic Susceptible host Large population of virulent pathogen Very favorable environment Over a large area Usually wind-borne Can be very expensive Even deadly
Important Terms Primary inoculum Secondary inoculum Symptom Sign Incubation period Latent period
Symptom Sign
Infection Many pathogens require a wound Some use “natural openings”
Stomates Lenticels
Some penetrate directly Mechanical Enzymatic Combination
Infection Some require a “vector” Provides mobility Provides wound
Insects (aphid, thrip, leafhopper) Fungi (powdery scab vectors PMTV) Nematode (Stubby root vectors TRV)
Causal agents of disease Viruses
Viroids Prions?
BacteriaActinomycetes phytoplasmas fastidious bacteria
Fungi Nematodes
Plant PathologyG. Agrios
Bacterial Diseases
Bacteria: Characteristics Very small Require microscopic techniques to see Biochemical techniques also needed Rapid generation times (20 minutes!?) Prokaryotic Rigid cell walls Phytoplasmas = no cell wall =
ameoboid
Bacteria: Characteristics Damage often due to enzymatic activity Some may clog vascular system
Specific Bacterial Diseases
Disease: Soft rot / BlacklegOrganism: Pectobacterium carotovorum
(=Erwinia carotovora)Symptoms: Foliar blackleg appears as a black
stem rot starting at the seed that kills the stem. Soft rotted tissues appear creamy and very soft, can become discolored and odiferous
Source and Spread: Inoculum originates from multiple sources and spreads during handling, field spread is in water
Key Features
Are everywhere Very opportunistic secondary invader Thrives with or without O2 Facultative anerobe Storage rot – major player Seed piece decay – major player Aerial stem rot
Soft rot bacteria
Disease: Bacterial Ringrot (BRR)Organism: Clavibacter michiganensis
subsp. sepedonicusSymptoms: Plants can show wilting and
leaf rolling, tubers show a slimy yellow exudate in the vascular ring
Source and Spread: Seed tubers provide inoculum which spreads during seed cutting and handling
Bacterial Ring Rot “BRR”
Key Features
Almost exclusively seed borne Zero tolerance in seed Confined to vascular tissues Can spread during seed cutting Survives on equipment and in storages
Bacterial Ring Rot
Disease: Common scabOrganism: Streptomyces scabiesSymptoms: Corklike scabby areas or pitted
depressions on the tuber surfaceSource and Spread:
Endemic to many soils or introduced on seed, infects upon contact with tuber skin
Key Features
Superficial only Only develops while tuber is growing Progress stops in storage “Cosmetic” disease
Common Scab
Fungal Diseases
Plant PathologyG. Agrios
Fungi: Characteristics Most plant diseases caused by fungi Larger, some can be seen with naked eye Also require microscopic techniques Biochemical techniques also needed Complex life cycles in some
Fungi: Characteristics Eukaryotic Multicellular Main body is thread-like “hypha” Many “hyphae” = “mycelium” Many form spores and other structures Spores sexual or asexual Overwintering and dispersal structures
Fungi: Characteristics Wind, soil, water, seed, equipment Single or multicycle Many ways of entering plant Foliar, tuber or both affected
Fungi: Characteristics Wind, soil, water, seed, equipment Single or multicycle Many ways of entering plant Foliar, tuber or both affected
Specific Fungal Diseases
Disease: Late BlightOrganism: Phytophthora infestansSymptoms:
Leaf and stems lesions, foliage destruction, tuber rot
Source and Spread:Seed, cull piles and volunteer potatoes provide inoculum, sporangia move with wind and water
Key Features
Most important disease of potatoes Responsible for Irish famine Very rapid disease development Spores windborne Must have wet conditions Effects foliage and tubers Recent changes in capabilities
Late Blight
Disease: Early blightOrganism: Alternaria solaniSymptoms:
Brown to black leaf lesions (bullseye) appear first on the older leaves, leaf death and defoliation, sunken surface tuber lesions
Source and Spread:Inoculum in soil overwinters on debris, moves onto the plants is from splashing water, additional spore movement in air and water , tubers infected during harvest
Early blight
Early blight
Early blight
Late blight
Key Features
Attacks senescing tissues May show up on lower leaves first Favored by alternating wet and dry Mostly foliage but tubers can be affected
Early Blight
Disease: Verticillium wiltOrganism: Verticillium dahliae or albo-atrumSymptoms:
Wilt of stems and leaves, early death of foliage, necrotic stem vascular streaking
Source and Spread:Inoculum occurs naturally in the field and overwinters on refuse, disease moves with seed and soil, only plants in infested fields are infected
Verticillium wilt
Verticillium wilt
Key Features
Soil borne disease One major reason for fumigation Some varieties worse than others Mostly wilt but some SED is possible
Verticillium wilt
Disease: Rhizoctonia CankerOrganism: Rhizoctonia solaniSymptoms:
Reddish brown lesions on underground stems and stolons that occasionally result in girdling or “damping off”, black “scurf” on the surface of mature tubers
Source and Spread: Overwinters in soil or on seed tubers as sclerotia which invade developing sprouts or stolons in the spring.
Rhizoctonia
Rhizoctonia
Key Features
Seed and soil borne Cankers girdle new shoots More susceptible before emergence Yield unchanged, quality affected Cosmetic = “dirt that won’t wash off”
Rhizoctonia
Disease: Fusarium tuber rot “dry rot”Organism: Fusarium coeruleum and sambucinumSymptoms:
After a period in storage brown lesions form under the tuber periderm, infection area enlarges and becomes sunken, tuber eventually mummifies
Source and Spread: Inoculum source is primarily seed tubers and is spread during seed handling, hyphae invade wounds
Fusarium sambucinum
Dry rotFusarium coeruleum
Key Features
Seed and soil borne? Must have a wound to infect tubers Cut seed tubers = huge wounds Seed piece decay Storage rot
Fusarium dry rot
Disease: Pink rotOrganism: Phytophthora erythrosepticaSymptoms:
Field infection can cause wilting but is primarily a tuber rot, spreads quickly and uniformly through the tuber, flesh rubbery but intact and turns pink upon exposure to air
Source and Spread: Endemic to some soils, spores infect tubers through stolons, lenticels, or buds
Pink rot
Key Features
Tissues remain relatively firm Rubbery texture Rot usually progress in straight line Tissues turn pink upon exposure to air Can be seen in field and storage
Pink rot
Disease: Leak, Pythium Watery wound rotOrganism: Pythium ultimumSymptoms:
Solely a tuber rot, starts as a discolored area around a wound, rot moves quickly through the flesh with a dark line demarcating line between infected and healthy tissue
Source and Spread: Endemic to most soils, enters tubers at wound sites during harvest and handling
Key Features
Must have a wound Associated with high pulp temperatures Very rapid decay Often rots center of tuber, leaving shell Tissues very soft Readily “leaks” clear fluid
Pythium leak
Diseases not discussed Powdery scab White mold Black dot Phoma Southern bacterial wilt Compendium of Potato Diseases
Disease Management Principles
Management Usually aimed at populations Single individuals not important EXCEPT Trees, other perennials
Management Diseases difficult to cure Most management aims at
protecting
Control Strategies Regulatory Cultural Biological Physical Chemical
Regulatory Aimed at excluding a pathogen from host or geographic area
Cultural Avoiding contact between plant
and pathogen Create unfavorable environment
or avoid favorable conditions Eradication or reduction of
inoculum
Biological Host resistance Microorganisms
antagonistic to pathogen
Physical and Chemical Protection from inoculum Curing an infection
Control Methods Exclusion Eradication Resistance Direct protection Integrated control
Guidelines for making disease management decisions
Before Planting Use only certified seed Fall fumigation? Spring not as good
At Planting Avoid unfavorable conditions Use a seed piece treatment
Fusarium dry rot Rhizoctonia stem canker/black scurf Late blight?
Single drop or healed seed In furrow fungicide applications
Growing season Fertility and water management Scouting, forecasting Fungicide applications may be needed for:
Early blight Late blight White mold
Insecticide for PLRV (virus - insect vector)
Vine Kill and Harvest Adequate time for skin set before harvest Wound-obligate pathogens Post harvest fungicides for some diseases
Phosphorus acid (late blight, pink rot) Biologicals (bio-save) (dry rot New post harvest under development
Storage Wound healing period Pesticides applied in storage? Tools for the storage manager
Air flow Temperature Humidity
Virus Diseases
Plant PathologyG. Agrios