This document discusses seed borne plant pathogens and their role in quarantine. It begins with an introduction to seed pathology and examples of historically significant seed borne diseases. It then describes the different types of seed infections (internal, external, admixture) and paths of seed infection. Detection methods are outlined, including dry seed inspection, seed washing tests, and incubation methods. The document stresses the importance of detecting seed borne pathogens prior to import/export to identify disease risks and ensure seed quality and health.

1. SEED BORNE NATURE OF PLANT PATHOGENS:
ROLE IN QUARANTINE
Presented By:-
Subash Thapa
L-2019-A-119-M
Department of Plant Pathology
Punjab Agricultural University, Ludhiana

2. Introduction
Effects of seed infection
History
Paths of Seed Infection
Detection and Management
Quarantine
Conclusion
SEQUENCE OF PRESENTATION

3. INTRODUCTION
Seed
Any plant parts which is used for commercial
multiplication of a crop
Seed is the product of fertilized ovule that
consists of embryo, seed coat and cotyledon
Out of total 90% of food crops grown in the
world are propagated through seeds(Schwinn
1994)
 Victims and vehicle of pathogens propagules
 Fungi, bacteria, viruses and even nematodes are
carried in the seed, on the seed or with the seed

4. Seed Pathology
Term Seed Pathology first used by
Paul Neergaard and Mary
Noble(1940)
Study of seed-borne diseases
Seed Pathology is a part of Plant
Pathology dealing with seed
diseases, their detection and
management
.

5. Why Seed Borne Pathogens are important?
1. Late blight of potato caused by Phytophthora infestans was responsible
for Irish famine during 1845
2. Brown spot of rice caused by the seed borne Helminthosporium oryzae
was responsible for Bengal Famine during 1942.
3. The loss by Downy mildew of pearl millet in Rajasthan in 1962-64 was
estimated to be 20 million rupees.
4. Occurrence of tobacco bud blight in soybean caused 66.43% yield loss.
(Dhingra and Chenulu 1980)
5. Philippines, losses due to blast may be more than 50%
Socio-economic impact

6. Alteration in Physical Properties of
Seeds
Physical properties such as
 Density
 Shape
 Size
 weight
fungal species such as Alternaria,
Fusarium and Phomopsis

7.  Production of Toxin
• Infection of seed by fungus leads to
production of different toxins
• Unsuitable for consumptions as feed
• Aflatoxin in peanut infected by Aspergillus
flavus
• Liver damage in case of feeding of rice grains
infected with Penicillium islandicum
• Hypertrophy in swine by Gibberella zeae
infected maize grains
• Abortion in cattle in case of feeding of
Claviceps purpurea infected grains
Infected Groundnut kernel with
Aspergillus

8. Discolouration and Shrivelling
Discolouration can indicate undesirable
physical qualities, the presence of toxic
metabolites or other unfavourable seed
characteristics
Loss in Germination and Vigour
e.g. Bipolaris oryzae (brown spot)-infected
rice seeds have been found to be lower in
germination than healthy seeds, Karnal bunt
infected seeds of wheat, 31-35% reduction in
germination in Alfalfa seeds infected by
alfalfa mosaic virus

9.  Inoculate Fusarium graminearum in different seeds like pea, lupine,
soybean, bean etc (10mL (1× 10 ^6 conidia per mL)
 Reduced germination energy by 2.56% and 7.79% respectively in pea and
lupine
(low germination energy = high susceptibility to infection)
Rasiukeviciute and Kelpsiene 2018

10.  Economical losses
Chronic yield losses by harmful organisms in rice in
tropical Asia
Savary et al 2000

11. Year Event
1755 Tillet, a French botanist, showed that stinking smut or hill bunt of wheat was caused by poisonous
substance on seed surface i.e. parasitic fungus
1883 Frank, described the internally seedborne nature of a fungus in bean seed
1892 Beach, in New York, proved the seedborne nature of a Bacterial pathogen Xanthomonas
axonopodis pv. phaseoli in common bean
1940 Noble, Scottish seed pathologist coined the term “seed pathology” (Paul Neergaard)
1942 Mayer, proved virus transmission through seed
1969 Chatrath, successful control of loose smut of wheat by seed dressing with carboxin
2007 H S Shetty, an outstanding Indian seed pathologist honoured with “Seed Health Award” for
immense contribution in the area of seed health and seed quality control for developing countries
Brief History

13. Delegates to the 1st Seed Pathology Workshop Seed Testing Station,
Cambridge, UK, 1958

14. Seed-borne Pathogens
Seedborne pathogens are defined as any infectious agent
carried on the seeds, internally or externally, that has the
potential to cause disease in either seeds or the developing
plants.
Seed-borne pathogen are classified into three different
groups:-
 Internally seed-borne pathogen
 Externally seed-borne pathogen
 Admixture

15. Externally Seed-borne Pathogens
On the surface of the seed in the form of conidia, mycelium or any
kind of resting spore e.g. Smut of pearl millet, flag smut of wheat,
common bunt, covered smut of barley
Anthracnose (Colletotrichum graminicola) of sorghum Karnal bunt infected seed of wheat

16. • Pathogen is present anywhere inside the seed. Can be
present below the seed coat, embryo or in endosperm
• e.g. Dormant mycelium in case of loose smut of wheat,
dormant mycelium of Botrytis anthophila in seed coat causing
blossom blight of red clover
 Internally Seed-borne Pathogens
Batts 1955

17. Admixture
Pathogen present along with the seed as a contamination
In the form of fruiting body of the pathogen like sclerotia
of Claviceps fusiformis causing ergot of pearl millet mixed
up the seeds (Pathak et al 1984)
Ergot of pearl millet

18. Major out breaks of seedborne diseases
in India
1) Ergot disease of pearl millet(Claviceps fusiformis) in 1956,
Maharashtra
2) Sunflower downy mildew (Plasmopara halstedii) in Maharashtra,
Potato Golden Nematode (Globodera rostochinensis) in Nillgiri Hill,
Wart disease of potato in Darjeeling
3) Late blight of Potato out break
4) Karnal bunt and rice bunt (Nevossia horrida)
5) Ripe rot of chili (Colletotrichum capsici) in Central part of MP

19. Seed Infections
The infestation/contamination of the seed may occur during harvesting,
threshing and processing. The pathogen may, thus, be carried with the seeds
in three ways :-
Harvesting Threshing Processing

20. Infection Process/Ability to gain
access to seed
 Active infection
- within seed
 Passive infection
- present on seed surface
- contaminant in seed lot

21. Routes of Active Infection
e.g.: Cladosporium
variabile(spinach), Botrytis spp.
(onion)
Weak necrotrophs:
• Botrytis cinerea infected petals remain
attached to developing fruit
Aggressive necrotrophs:
• Attack floral parts directly, e.g.,
Ascochyta pisi, Alternaria brassicicola
Penetration through ovary wall

22. Continue….
E.g.: Vascular wilt fungi,
endophytes
 Many viruses, e.g.:
• PSbMV on pea
• LMV on lettuce
• AMV in alfalfa
 Some fungi, e.g.:
• Vascular wilts (Verticillium dahliae, Fusarium
oxysporum)
some downy mildews
 Few bacteria, e.g.:
• X. campestris pv. Campestris, X. Campestris pv.
phaseoli
Systemic infection via vascular system

23. Continue….
e.g.: Ustilago nuda(grains)
 Pathogen moved from infected plants to Flowers
 follow pollen pathway to embryo sac
 Examples:
• pollen borne viruses – LMV, CMV
• Nepoviruses
• Loose smut of wheat(Ustilago tritici)
• Loose smut of Barley(Ustilago nuda)
Maude 1996
Penetration through floral parts

24. a. Healthy embryo(left) and embryo with hyphae of U. nuda
b. intercellular hyphae in scutella tissue
c. Shoot apex of 4-day old seedling with hyphae in the scutellum
d. Hyphae growing into the shoot apex
e. Shoot apex and leaf primordia colonized by hyphae (10–14 days after sowing)
f. Invasion of ear primordium (30 days after sowing) Wunderle et al 2012
Embryo Infection

25. • infection shortly before, during, and two days after the flowering period
• the spores quickly germinate and grow down the stigma and pistil–the
female parts of the flower–to invade the young embryo
• the mycelium of the smut fungus again becomes active and grows systemically
into the young shoots to the growing point
• spikelet's in an infected wheat head are completely transformed, except for a
pericarp membrane, into a dusty mass of teliospores
Abrahim 2019

26. List of seed borne pathogens
Fungal
Fusarium graminearum
Alternaria solani
Ustilago tritici
Alternaria triticina
Ustilago nuda
Bipolaris oryzae
Magnaporthe grisea
Fusarium moniliforme
Colletotrichum truncatum
Cercospora sojina
Bacterial
Xanthomonas campestris
pv. carotae
Xanthomonas campestris
pv. citri
X. oryzae pv. oryzae
X. oryzae pv. oryzicola
Virus and Nematodes
Tobacco ring spot virus
Bean common mosaic
Lettuce Mosaic Virus
Tobacco Mosaic Virus
Bean Yellow Mosaic
Potato X virus
Potato Y virus
Cucumber Mosaic Virus
Anguina tritici
Heterodera glycines

27. Detection of Seed Borne Pathogens
Seed borne pathogens plays important role in
import and export of seeds
Different detection methods to certify the lots
prior to import/export
 identifies potential disease problems and
allow steps to be taken to reduce the disease
risk
Involve lab testing as infected seed may not be
having visible disease symptoms
 ISTA, ISHI and NSHS are three primary organizations
that publish standardized seed health test methods
(Munkvold 2009)

28. Upadhyay et al 2019
Techniques for Detection
Conventional Serological Nucleic Acid Based
 Naked eye dry seed inspection
 Seed wash test
 Whole embryo count test
 Incubation tests
 Grown on test
 Infectivity test
 X-ray radiography
 Histopathological test
 Seedling symptom test
 ELISA
 DIBA
 SADI
 ISEM
 Immunofluorescence
 DA
 ELFA
 RFLP analysis
 PCR
 Nested PCR
 Rep-PCR
 BIO-PCR

29. Detection of seed borne pathogens methods
 Non-incubation methods
1. Dry seed inspection (visual examination)
2. Seed washing test
Incubation methods
1. Blotter test
2. Agar test
3. Seedling symptoms test
Detection of seed borne pathogen is the first line approach in
managing seed borne diseases of plants (Hajihasani et al 2012)
Kumar 2020

30. 1. Dry seed inspection
 qualitative test through visual observation
Different parameters like discolouration,
abnormal shape & size
Sclerotia, fungal mycelium growth
 Inspection Procedure
• Acquire sample
• Careful observation(sclerotia, smut balls,
spores etc)
• Hand held lens
• E.g. ergot of sorghum, bunt of wheat,
wheat seed gall

31. 2. Seed washing test
 Solely for fungal seed borne pathogen
 Seed suspended in known amount of
distilled water
 Procedure
• 50g seed in 100mL distilled water in Erlenmeyer
flask and 1 drop of tween 20
• Shake(5min) and sieve
• Observe under microscope adding one drop of
shears solution
• E.g. downy mildew of sunflower( Plasmopara
halstedii), pear millet( Sclerospora graminicola)

32.  Blotter test
 Incubation of seed for 7 days at 20-22°C
 Procedure
 Incubate seed(10-25 per plate) in petri
dishes bedded with sterile distilled water
soaked filter papers(Blotters)
 Incubate it for 7 days at 20-22 °C
 Examination of seeds under microscope
after 7 days
 E.g. Alternaria solani, Fusarium
oxysporium, Colletotrichum
lindemuthianum

33. Seedling symptoms test
 Seeds are planted in sterile soil or in
paper towels
 After germination of seed provided with
normal condition for germination,
seedlings are observed for characteristic
symptoms e.g. Fusarium spp. In cereals
and Ascochyta spp. in pea
 Basically done through
• Paper towel test
• Growing on test

34. General features of seed detection assays including the time required for completion,
sensitivity, ease of application, specificity, and applicability for the detection of fungi, bacteria
and viruses
Walcott 2003

35. Maximum Permissible Limits and Method for Detection of Seed Borne
Diseases
Source :- Seed Standards
https://seednet.gov.in/

36. Role in Quarantine

37. • Primary source of infection for
several destructive diseases
• Excellent carrier for the
spread of pathogens to long
distances
• International trade and exchange of plant
germplasm
• Global movement of seed material is
associated with the risk of introduction of new
pathogens into the country of import
• Leading to serious yield losses

38.  The Irish famine of 1845, due to total failure of potato
crop because of late blight pathogen introduced from
Central America, forced the people to migrate from
Europe
 Sri Lanka in 1875 and by 1889, coffee rust caused by Hemileia
vastatrix appeared, reducing coffee production by >90%
 Entered India in 1876 from Sri Lanka
 Lacking appropriate phytosanitary measures and the
indiscriminate germplasm exchange by international agencies
Khetarpal et al 2006

39. Quarantine
• Latin words quarantum
• Quarantine = 40 days
• Plague epidemic in Europe (1347-53)
Plant Quarantine Centre

40. Plant Quarantine
 Legal restriction on movement of agricultural commodities
 Exclusion, prevention or delay in the establishment of plants, pests and
diseases in the area where they are not present
 Safeguard against harmful pests/pathogens
Worldwide invasion history of Plasmopara viticola Fontaine et al 2020

41.  The first plant quarantine was passed 1660, France(wheat stem rust)
 Federal quarantine service established in Australia – 1909
 Directorate of Plant Protection, Quarantine and Storage(DPPQS)
established in 1946 located at Faridabad, Haryana
 First Plant Quarantine and Fumigation Station Dec 25,1951
 National Bureau of Plant Genetic Resource (NBPGR) August, 1976
 Division of Plant Quarantine with Entomology, Plant Pathology and
Nematology sections 1978
 Plants, Fruits and Seeds (Regulation of import into India)
PFS October , 1988
HISTORY
Rai Vijay Lakshmi et al 2014

42. Domestic Quarantine
• Legal restriction within state to state
• To prevent the spread of introduced exotic pest or an indigenous
key pest to pest-free areas within the country
• Examples of restricted inter-state movement diseases:-
 Banana bunchy top virus(Assam, Kerala, TN and W.B.)
 Banana mosaic virus(Maharashtra and Gujarat)
 Potato cyst nematode(Nilgiri district of TN)
 Potato wart (Darjeeling district)
 Apple scab (JK and HP)

43. Pests and Diseases introduced in India from other
countries Chand et al 2017

44. PHYTOSANITORY CERTIFICATE
 What is a Phytosanitary Certificate?
A Phytosanitary Certificate is an official document
- Issued by the Horticulture and Plant Health Division of the Department of
Agriculture, Food and the Marine to indicate that consignments of plants, plant
products or other regulated articles meet specified phytosanitary import meets the
requirements of the National Plant Protection Organisation (NPPO) of the Importing
Country
(http://www.agriculture.gov.ie/farmingsectors/planthealthtrade/)
When should a Phytosanitary Certificate be required?
 Importing Countries should only require phytosanitary certificates for regulated
articles. These include commodities such as plants, bulbs and tubers, or seeds
for propagation, fruits and vegetables, cut flowers and branches, grain, and
growing medium

46. Seed treatments
Pathogens Plant parts Temperature Time
Nematodes Flower bulbs 44°C 240 min
Chrysanthemum 48°C 25 min
Potato tubers 45°C 5 min
Viruses Grape vine 45°C 120-180 min
Sugarcane setts 50°C 120 min
Potato tubers 50°C 17 min
Fungi Celery seed 50°C 25 min
Wheat seed 52-54°C 10 min
Hot water treatment

47. Solar Heat Treatment (Luthra and Sattar 1953)
Soaking Drying
Storage
Salt water treatment: brining (bunt)

48. Microwave Radiation:-
• Applied microwave radiation to red lentil seeds
• Subjected at different level of exposure time
• Infected seeds decreased from 17 to 9% at exposure time of 51 second
Taheri et al 2019

49. Chemical treatments
• Systemic fungicides:-
Carboxin for control of smuts; Benomyl
for control of Ascomycetes; Metalaxyl for
control of Oomycetes
• Non-systemic fungicides:-
Copper compounds for control of
bacteria and fungi; Captan, Difolatan and
Maneb broad spectrum

50.  Coating with biological control agents( Pseudomonas, Bacillus,
Trichoderma, Phomopsis, Gliocladium etc)
 Biological fungicides are a relatively new tool available
• Trichoderma viride sensu (Trade Name:- F-Stop) for seed
treatment in tomatoes
• e.g. Loose smut of wheat (cv. HD 2189), caused by Ustilago
segetum var. tritici, was controlled almost completely through
seed treatment with any of the biological agents like
Trichoderma viride, T. harzianum, Pseudomonas fluorescence and
Gliocladium virens in combination with vitavax (carboxin) at
0.125%
 Biological Treatment

51. Rajput and Rao 2019

52. Mishra et al 2015

53. Conclusion
Seed transmission of pathogens is the most important mode of carry
over from season to season and easy mode of long distance
dissemination
Distribution of pathogens, new strains or physiological races of
pathogens along with the introduction of germplasm to new countries
or areas
Proper diagnostic methods and treatments(effective and
efficient)
Great need to revisit the existing domestic quarantine scenario for
strengthening interstate quarantine check-posts
Molecular techniques for detection of pathogens in quarantine
assume great significance but need to be improved for high
throughput and user-friendliness