SEED BORNE DISEASES

1. SUBMITTED BY RAMESH KUMAR THAKUR
SEED SCIENCE AND TECHNOLOGY.
MANAGEMENT OF
SEED
BORNE DISEASES

2. Management of seed borne
diseases can be done through:
 Crop production practices
 Seed treatment
 Seed certification
 Plant quarantine

3. 1. Management through crop
production practices.
 For production of quality seed the grower has to follow
some practices like:
 Crop should be maintained & inspected carefully to
produce clean seed.
 Additional care should be ensured for genetic purity,
freedom from diseased & weed seeds, etc.
 Seed crop should be grown in regions with minimum
disease pressure.
 Disease resistant varieties has be preferred.

4. Management practices to be considered at
different crop stages are :
1) Before planting the seed
2) During crop establishment
3) During flowering & seed development
4) During seed maturation
5) During harvesting, threshing & processing
6) During storage

5. 1) Management before planting:
a) Selection of site:
 Factors critical for successful seed production are
climatic conditions, previous crop history, weed
population, disease history, isolation, position of
field in relation to other key areas, the nature of the
soil, water & other physical features of that site.
 The disease pressure is often regionally based.
 Risk of disease infection varies widely by crop,
disease & location.
 In India, incidence of Karnal bunt of wheat is
promising in Northern states.

6. b) Sanitation
Destruction of crop residues is done based on
the type of crop, type of pathogen & size of the
crop.
Burying the residues – S. oryzae, X. campestris
pv. malvacearum.
Burning of the debris – sclerotia which is the
primary source of inoculum in perennial
grasses in seed production fields.
Sanitation of pruning implements, inter
cultivators, etc. which may carry viral
infections. Eg: TMV

8. c) Weed & insect control
 In addition to detrimental effect on yield some
weeds also serve as reservoir of many seed borne
pathogens.
 Rice tungro virus, paddy blast, certain rusts
cannot complete their life cycle without alternate
host- where sexual recombination occurs.
 Perennial weeds around the fields act as over-
wintering hosts for harmful viruses
 Insects like aphids, leaf hoppers, trips & beetles
not only feed on plants but also spread many viral
diseases.

9. d) Soil conditions & soil types
Soil type, texture, aeration, acidity or
alkalinity, suppressive-ness, soil
temperature are certain factors responsible
for seed & soil borne diseases.
Covered smut of wheat is more severe in
low soil temperature & high soil moisture.
Soil temperatures <29.5C inhibits soybean
growth, promotes seed rot & damping off,
particularly if soils are wet.

10. e) flooding
 It can reduce weeds, number of fungal
propagules, insects & nematodes in the
soil.
 Flooding reduces Hill bunt (T. laevis)
incidence in wheat.
 Flooding causes destruction of crop debris
& it also carries the propagules of some
pathogens growing in the flood water.

11. f) Fertilization & crop
nutrition
 Excess use of N increases the incidence of rice blast,
bacterial blight in rice, Kernal bunt in wheat &
rhizoctonia seedling blight of pea, beans & vegetables.
 Late application of N in wheat increases leaf blotch.
 Deficiency of N or P results in take-all disease in wheat.
 Excess Ca in soil- reduces bean root rot but favours
head smut of sorghum.
 Ferric chloride- reduces rice brown spot
 Sillica- reduces rice blast.
 Molybdenum- reduces Ascochyta blight on beans &
peas.

12. G) Manuring
Nutrients released from decomposing
residues stimulate the activity of some
pathogens but they don’t have host to attack
& they die.
Soil incorporation of green manure as cover
crops can be used effectively to reduce root
rot pathogens.
Alfalfa is effective in suppressing disease
organisms in soil.

13. h) Crop rotation
Successive planting of different crops in the same
area, sometimes with fallow or resting period
between crops.
 It helps to reduce the buildup of root-rotting
organisms.
 Pepper may not be followed with Solanaceae
crops as these crops share many soil-borne
diseases.
 Crop sequencing of cotton, sunflower and maize
increase the infection of Macrophomina
phaseolina.
 Once in 4 year rotation in lentil helps to reduce
Ascochyta blight incidence.

14. i) Resistant/Tolerant
cultivars
It is the best & cheapest method of disease
control.
The term resistance describes the plant
host’s ability to suppress or retard the
activity & progress of a pathogenic agent
which results in absence or reduced of
symptoms.
Tolerant plants can endure severe disease
without suffering significant loss in yield.

15. conti…..
Black seeded varieties in gram are more
resistant to Ascochyta blight than white
seeded varieties- presence of phenolic
substances inhibitary to the pathogen.
Coloured testa in ripened bean seeds inhibit
C. lindemuthianum.
Anti-microbial substances in seed coat of
bean, pea & sweet pea inhibit seed infection
by C. flacumfacience pv. flacumfacience.

16. 2.MANAGEMENT DURING
CROP ESTABLISHMENT
A. Clean planting material /Disease free seeds
& transplants:
 Use of healthy seeds can help growers to
avoid many costly & environment damaging
fungicides in later season.
Results showed that farmer’s fields used clean
seeds decreased transmission of rice seed-
borne diseases such as brown spot, red stripe,
leaf scald, bacterial leaf blight, sheath rot and
grain discoloration.

17. b) Sowing practices
Change in time of sowing may exploit
weather conditions that are unfavorable to
the pathogen & reduce yield losses.
Deep sowing favours covered smut, flag
smut & Kernal bunt in wheat, & loose smut
in sorghum.
Narrow spacing & dense seedling reduces
aeration & provide humid canopy that
encourages the introduction & spread of
disease.

18. c) Tillage practices
It has indirect effect on spread of disease.
Some forms of inoculum spread
extensively during tillage.
Tillage buries pathogens present on the
top soil deeper where they are less likely
to cause the disease.
Also helps in release of nutrients in soil &
benefits the crop.

19. d) intercropping
Practice of growing more than one crop in
alternate rows.
Reduces disease by increasing the
distance & creating physical barrier
between the plants of same species.
Successful intercropping partly depends
upon combination of crop plants chosen.

20. e) Soil amendments
Organic amendments increases the
activity of competing or predatory
microorganisms in the soil.
They also help in rectifying the problems
related to soil pH & make nutrients
available to plant.

21. f) Irrigation & drainage water
Overhead watering can prolong the leaf
wetness- increases likelihood of germination
& infection by fungal spores.
Excess irrigation – favours Karnal bunt
Frequent irrigation- reduces flag smut of
wheat
Alternate wetting & drying destroys
sclerotia.
Drip irrigation delivers water directly to root
zone & at rate insufficient to disperse
pathogen.

22. g) Trap crop
Trap crop are susceptible plants grown on
land containing pathogens, they become
infected & destroys before pathogen
completes its life cycle- reducing the
amount of inoculum in the area.

23. h) Roguing
Removal & destruction of diseased plants
as soon as disease symptoms are observed.
In sorghum & pearl millet ergot ear heads
are rogued & burnt.
In viral diseases effective roguing reduces
the spread of the pathogen.

24. i) Isolation
The distance between the seed production
& commercial plots is maintained to
reduce disease incidence in seed crop.
This distance varies from region to region
based on weather conditions.
For loose smut of wheat & barley isolation
followed is 150m

25. 3. MANAGEMENT DURING FLOWERING
AND SEED DEVELOPMENT
a) chemical protection in the field:
 Several seed borne fungi, such as Colletotricum
sp., Alternaria, Tilletia sp. etc. and viruses such as
lettuce mosaic virus, bean common mosaic virus,
cucumber mosaic virus etc. become established in
seed during flowering, seed setting and maturation.
 Prophylactic measures using timely application of
appropriate fungicides/chemicals/insecticides or
bio agents, from early blossom to maturity of the
crop at an appropriate stage of the plant growth is
one of the effective management practice.

26. 4. MAGEMENT DURING SEED
MATURATION
 Fungal infection of seed is often more pronounced
during the later stages of maturation, especially in
areas where seed maturation coincides with the
season of high atmospheric humidity.
 The rainfall from maturity to the harvest of the
crop appears to effect the incidence, prevalence
and severity of seed borne fungal pathogens.
 If excessive rainfall occurs during harvest, the
colonization and infection of the pods and seeds by
pathogens and saprophytic fungi cause seed
discolouration.

27. 5. MANAGEMENT DURING
HARVESTING, THRESHING AND
PROCESSING
 Harvesting equipments are adjusted for
minimum kernel or seed damage and maximum
cleaning.
 Timely harvesting and processing avoids the
anthracnose infection which usually occurs on
mature fruits.
 After proper processing, subsequently stored
under low temperature and low moisture content
to avoid contamination in storage.

28. 6. MANAGEMENT DURING
STORAGE
Most storage fungi belong to the genera
Aspergillus, Pencillium, Rhizopus, &
Chetomium.
Storage fungi are frequent where seed
moisture level is above safer level
(>10%).
A. niger attacks seed at moisture content
of 12% at RH 75%.

29. 2. MANAGEMENT THROUGH
SEED TREATMENT
Physical methods:
 Seed dip in water: soaking seed in plain
water at 20°c for 41 hrs- loose smut of
wheat.

30. Hot water treatment:
The seeds are dipped for specific period of
time in hot water to a particular temperature
safe to the seed embryo and deleterious to
the associated pathogen
Useful for low volume high value seed
Effective for internally associated fungi and
bacterial pathogens.
High temperature damage the embryo
Temperature and duration of treatment
differs from crop to crop

31. Hot air treatment
The seed material is exposed to hot air
stream for a specific period, which is
safe for viability of seed.
More effective for the pathogens
associated on to the seed surface.
Eg: Tomato mosaic virus of tomato -3
days at 70 °c

32. Solar heat treatment
Safe and convenient method than hot
water treatment.
J. C. Luthra suggested this method for
control of loose smut of wheat.
Wheat seed is presoaked in water for 4-5
hrs in the shade or in a room and then
dried on ground /concrete floor in a thin
layer in sun for 1 hr usually at noon time
to eradicate the pathogen established
inside the embryo.

33. Biological methods
It aims at eradication and control of the
pathogen through antagonistic activity of
micro organisms which is achieved by
parasitism, predation and commensalism etc.
Some biological agents are :
 Trichoderma spp.
 Trichoderma viride, T virens
 Trichoderma harzianum
 Bacillus subtilis
 Pseudomonas fluorescens etc.

34. Chemical Seed Treatments
Application of chemical to seed is cheapest
method & most effective method for
controlling seed borne pathogens.
Fungicidal seed treatment may kill or inhibit
seed born pathogens by forming protective
covering.
 FORMULATIONS:
Seed treatment chemicals are available in different
formulations.
Dusts
Slurry
Liquid
Fungicidal-insecticidal formulation

36. Benefits of Seed Treatment
 Protects germinating seeds and seedlings
from soil and seed borne pathogens /
insects
 Seed germination enhancement
 Uniform crop stand, even in adverse
conditions (less/high moisture)
Treated Untreated

37. SEED CERTIFICATION &
SEED QUALITY CONTROL
 It was potato seed certification, began in
Germany (1990s) & soon after in US,
with the aim of stooping the spread of
viruses responsible for leaf roll & other
viral disease.
 Certification goes hand in hand with
seed quality control in which the most
important seed qualities are viability,
purity & health.

38.  Certification involves strict procedure for
labeling & sealing seed packs.
 Certification is limited generation system
based on 4 seed classes.
 Certification shall be completed in 6
phases.
 Compulsory requirements to be followed
for certified seed production: application,
field eligibility, isolation, field inspection,
offtypes, weeds, diseases.

39. PLANT QUARANTINE
SERVICES.
 Quarantine is a legislative (regulatory)
attempt to exclude pathogens from
invading into the areas where they do not
exist by monitoring the import and export
of plant, seed or planting material to
prevent spread of diseases and pests.
 It aims to prevent the entry of dangerous
pathogens but not the movement of
biological material.

40. References :
 Seed technology by: Dr. Harpal
SingTomar
Seed science and technology: Subir
Sen& N.Gosh
tnuagriportal.com
Wikipedia
Google