Seed Pathology Overview Agron 338, Seed Science and Technology • Dr. Gary Munkvold • Professor of Plant Pathology [email protected]515-294-7560 • Seed pathology (Agarwal & Sinclair, 1997) – the study of seedborne diseases and pathogens (includes other propagative materials) • Seed pathology (Munkvold, 2008) – the study and management of diseases affecting seed production and utilization; disease management practices applied to seeds Seed pathology - terms • Seed health refers primarily to the presence or absence of disease-causing organisms, such as fungi, bacteria and viruses, and animal pests, such as eelworms and insects, but physiological conditions such as trace element deficiency may be involved. Seed health testing deals with detection and identification of seed-borne microorganisms. • Seed quality is a concept made up of different attributes, namely purity, moisture content, and germination. Seed pathology - terms Source: Danish Seed Health Centre: http://www.dshc.life.ku.dk/ Seed Quality Characteristics • Germination ability • Vigor • Analytical (mechanical) purity • ‘Pure live seed’ = (%purity × %germination)/100 • Varietal (genetic) purity • Seed health (absence of seedborne/seed- transmitted pathogens) Encyclopedia of Seeds, 2006 Seed Quality Characteristics cont. • Moisture content • Uniformity Additional seed quality parameters: • Seed size • Visual appearance • Seed treatment quality (dose and uniformity) Encyclopedia of Seeds, 2006 1. Plant pathology review • What is plant disease? • Biotic vs. abiotic disease vs. injury • Types of pathogens • Disease triangle • Effects of diseases on plants
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Seed Pathology Overview Agron 338, Seed Science and Technology
• Seed health refers primarily to the presence or absence of disease-causing organisms, such as fungi, bacteria and viruses, and animal pests, such as eelworms and insects, but physiological conditions such as trace element deficiency may be involved. Seed health testing deals with detection and identification of seed-borne microorganisms.
• Seed quality is a concept made up of different attributes, namely purity, moisture content, and germination.
Seed pathology - terms
Source: Danish Seed Health Centre: http://www.dshc.life.ku.dk/
“…when the ability of the cells or part of a plant to carry out one or more essential functions is interfered with by a pathogenic organism or adverse environmental factor, the activities of the cell are disrupted, etc.,… the cells malfunction or die…”
Agrios, 2005
What is plant disease?
• Normal cell or plant functions are disrupted (efficiency is reduced)
• Caused by a prolonged interaction with another organism or abiotic factor
• A process, not a physical entity
Disease triangle
Temporal, quantitative
Plant pathogens
• Fungi & Oomycetes
• Bacteria
• Viruses and viroids
• Phytoplasmas
• Nematodes
• Parasitic plants
Agrios, 2005
Fungi
• Kingdom Mycota
• Microscopic, filamentous or single-celled, eukaryotic
• Cell walls composed of chitin & other compounds
• No chlorophyll
• Spore-producing
Bacteria
• Kingdom Procaryotae
• Microscopic, single-celled,
prokaryotic
• Cell membrane and cell walls
• Reproduction by fission
• Phytoplasmas
• Lack cell walls
Viruses
• Nucleic acid strands + coat
protein
• Obligate parasites
• Reproduce by utilizing host
biosynthesis processes
Nematodes
• Kingdom Animalia
• Microscopic, unsegmented
worm-like organisms
Lance Nematode
Stunt Nematode
Nematodes
Agrios, 2005
Agrios, 2005
Agrios, 2005 Stem rust disease cycle
Pythium disease cycle
Agrios, 2005
2. Seed Pathology
• Seeds implicated in plant disease for millennia
• Seed treatment suggested in 1733
• “Seed pathology” initially consisted of detecting and identifying seedborne organisms
• Paul Neergaard – first seed pathology publications and textbook
2. Seed Pathology overview
• Disease management in seed production
• Seed conditioning
• Seed infection processes
• Seed storage
• Seed health testing
• Seed transmission
• Seed treatment
• Seedling diseases
Environments for Seed – Pathogen
Interactions
SEED PRODUCTION FIELD
PLANTED FIELD
HARVESTING
PROCESSING
STORAGE
INFECTION DISEASE DEVELOPMENT
TRANSMISSION
SPREAD SURVIVAL
Cultural practices
Disease resistance
Chemical control
Inoculum thresholds
Cultural practices
Disease resistance
Seed health tests
Seed treatment
Seed conditioning
Environmental control From McGee, 1995
Disease management in seed
production – why is it different? • Crop value
• Seed quality –Performance
–Appearance
• Quarantine issues
• No flexibility in genotype
choice
• Limited location flexibility
•Limited crop rotation
•Environment
Association of pathogens
with seeds • Seedborne
• Pathogen – accompanying, external, or internal
• Seed-transmitted • Pathogen passes from seed to plant • Transmitted vs. transported or
disseminated
• Seed as a pathway • Seedborne or seed-transmitted • Pathogen can be introduced and
established through seed
Classes of Seedborne
Microorganisms 1. Pathogens for which seed is the major
inoculum source, and when seed infection is
controlled, the disease is controlled.
2. Important pathogens of a crop, but the infected
seed is a minor inoculum source.
3. Seedborne microorganisms that have never
been shown to cause disease as a result of
their presence on seeds.
4. Pathogens that can infect seed either in the
field or in storage, and reduce quality.
1
3
2
4
• Hand sorting – Discard insect-damaged and diseased
ears
• Drying and shelling – Arrest fungal development; discard
glumes and damaged kernels
• Air screen cleaning – Discard glumes and damaged kernels