Seed healthy : Seed healthy El-Sayed El_azazi
2012 What is seed health? : What is seed health? seed health refers to the presence or absence of disease-causing organisms such as fungi, nematodes, bacteria, viruses and insects, and to the status of seeds in a seedlot. Seed status is also affected by the presence of non disease-causing contaminants in the particular seedlot. These include contaminants like weed seeds that compete with the target seed for nutrients. Other seeds, plant parts other than the target seeds, soil particles and insect eggs that can overwinter can degrade the quality of the seedlot. The importance of seed health : The importance of seed health Why is seed health important?
Planting value (germination, vigor, short longevity,…)
Food/ feed quality ( infection, mycotoxin, aflatoxin)
Germplasm conservation ( G%, V%, GR,….)
Yield reduction (…..up to 100%) Example on role of Infected seed : Example on role of Infected seed Ascochyta fabae
0.2 % infected seed 15 %infected plants.
Ascochytae rabiei (chickpea)
7.7% infestans 100 % infected plants
Phytophara infestans (potato)
1 lesion 1 billion lesions/ season.
PV 1 infected seed /16000 100% infected plants The importance of seed exchange : The importance of seed exchange Seed is an important exchange material for farming, seed production and research at national, regional and international level. At international levels, seed exchanges help create new varieties of crops and materials for research. The worldwide exchange of germplasm has played a key role in the development of modern agriculture. Germplasm with good agronomic traits have been introduced into crops to improve them. An example of this is rice. Risks of seed exchange : Risks of seed exchange However, with seed exchange comes the danger of introducing pests and pathogens. Seed has the ability to harbour microorganisms for considerable periods of time, especially pathogens, microorganisms that can cause disease. Today, we recognize that seed is highly effective in introducing and disseminating pathogens from one area to another. In addition, seed provides a good environment for pathogens to survive from one season to the next. These hazards may accompany, adhere to, or be inside the seed.
Loss of germplasm due to seed and seedling death
Spread of seed-borne diseases in the field and across national or international boundaries Methods of detecting pests and pathogens : Methods of detecting pests and pathogens Seed-health standard
Examine a representative sample of seeds for the presence of pathogens using one or more of the following methods. Usually, a sample of 400 seeds in replication of 100 seeds each is drawn for
examination. Sample size can be decreased for small seed lots.
If the percentage of seeds infected is greater than 5%, the seed lot can be considered unsuitable for conservation. Visual examination : Visual examination The simplest method to detect diseases and pests is to examine dry seeds with the naked eye or under a low-powered microscope.
This method reveals freely moving insects, eggs, mites, fungal
fructifications like sclerotia, galls, smut balls, bacterial masses and infected plant debris. Examination of dry seeds under ultraviolet or near-ultraviolet light reveals infections of certain fungi and bacteria through emission of fluorescence. Seed-washing technique : Seed-washing technique This is useful for testing surface-borne, contaminating fungi such as smuts, bunts, downy mildews, powdery mildews and rusts.
1. Place 2 g of the seed sample in a test tube, add 2 ml of sterile water and mix well for five to ten minutes.
2. Centrifuge the supernatant solution at 200 rpm for ten minutes and observe the sediments under a microscope for fungal structures. Incubation methods : Incubation methods Blotter test
Blotter tests are similar to germination tests in that seeds are placed on moistened layers of absorbent paper and incubated under conditions that promote fungal growth.
1. Line the base of sterilized Petri dishes with three layers of
absorbent paper moistened with sterile water.
2. Drain off excess water and place 20–25 seeds manually with
3. Evenly space the seeds to avoid contact.
4. Incubate the seeds under near-ultraviolet light in alternating
cycles of 12 hours light/darkness for seven days at 20°+2°C.
5. Examine the Petri dishes under a stereo-binocular microscope
for fungi developing on the seeds.
Profuse seedling growth may make interpretation difficult. This
may be overcome by adding 2,4-D sodium salt to provide a 0.2%
moistening solution. Seed treatments : Seed treatments Fumigation – with phosphine at 2 g/m2 to destroy storage insects
Fungicide treatment – with benomyl and macozeb to control fungal pathogens that are surface-borne on the seed and internally seed-borne
Hot water treatment 52°C to 57°C for 15 minutes after presoaking in cold water for 3 hours to control white tip (Aphelenchoides besseyi), a disease caused by nematode
Sodium hydrochloride seed wash – to control kernel smut (Tilletia barclayana)
Low temperature treatment (-18 or -20 for 7 days Pre-shipment treatments To : Pre-shipment treatments To Fumigation – all seeds must be fumigated
Fungicide treatment – all seeds must be treated with fungicide
Hot water treatment - if seeds are infected by nematode
Low temperature treatment…. If seeds infested Slide 18: HOT WATER TREATMENT Advantages:
Kills disease on both inside and outside of seed
Can fully eradicate heat-sensitive pathogens
requires an investment
Requires careful handling, can damage seed
Can’t be done as easily during harvest, so often requires wetting and re-drying seed Slide 19: Hot Water Requirements 42-50°C (118-122°F)
Seed fully immersed, typically in cotton bags
NEED a setup with temperature control
Budget option is deep fryer (~$50-150)
Better option is lab-grade water bath incubator (~150-800 on ebay) Slide 20: Shaking Water bath Slide 21: Bleach Treatment Advantages:
Fast, easy, requires little to no special equipment
Can be done during washing of wet-seeded crops
Good for reduction but not eradication of disease
Only organic option for large-seeded crops that can’t be hot water treated
Not likely to completely eradicate disease
Requires careful handling, can damage seed coat
Kills disease only on seed coat, not internally Slide 22: Bleach Requirements Soak seed in a 5-10% bleach solution
usually 5-10 minutes
Can be done by adding bleach to final wash on wet seed harvest Documentation : Documentation Suggested descriptors to document accession-level information on
seed health-testing include the following:
• Source of the material for testing
• Type of material (leaf, stem, root, seeds)
• Number of plants sampled and tested per replicate
• Number of replicates
• Organisms tested for
• Method of testing
• Date of test
• Duration of test, if appropriate
• Diseases identified
• Incidence of each disease (%) Thank you +email@example.com@moe.gov.qa : Thank you +firstname.lastname@example.org@moe.gov.qa