1. SARAH ASHFAQ
BSADP-BT51F21
BS 6th Sem. ADP Replica
Presented To : Prof. Dr. Najam Ul Sehar
Topic: Apple Scab Disease
Institute of Botany , University of the Punjab 1
3. Introduction
Apple scab is a common disease of plants in the rose family Rosaceae that is
caused by the ascomycete fungus Venturia inaequalis. The earliest official
reports of apple scab were made in 1819 by Swedish botanist, Elias Fries.
Apple scab occurs everywhere in the world where apples are grown and results
in more losses than any other apple disease. It is most serious in areas that have
cool and wet spring weather.
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5. Symptoms
1. Apple scab infections are initiated in early spring on emerging and young leaves.
2. Early lesions appear 10 days later as lighter green areas compared to the
surrounding leaf tissue.
3. Lesions increase in size and become olive-colored and velvety as a result of
asexual spore production (conidia).
4. Fruit lesions are generally blistered and "scabby" in appearance, with a distinct
margin.
5. fruit distortion.
6. Petioles, flowers, sepals, pedicels, young shoots, and bud scales can also
become infected.
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6. Figure 1. Early lesions are olive-colored (A)
and velvety with no distinct margins (B).
Figure 2. Affected leaves
become distorted and puckered
Figure 3. Fruit lesions appear blistered and
scabby(A) with distinct margins (B).
Figure 4. Infections of young
fruit cause distortion as fruit mature.
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8. Step 1. Pseudothecial
initial develops into
a pseudothecium. Arrows
show hyphae,
which may represent the
two mating types.
Step 2. Asci and ascospores form
inside a
pseudothecium. Asci and
ascospores may
be stained (not shown) for
enhanced viewing.
Step3. Asci of Venturia
inaequalis containing
eight ascospores.
Arrows highlight
individual ascospores.
SEXUAL REPRODUCTION
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9. Step 4.The ascospores are
brown, two-celled spores,
and have a characteristic
"footprint" shape .
Step 5.During wet conditions,
mature pseudothecia swell and
protrude from the surface of fallen
leaves Ascospores are released
and carried to blossoms and
leaves by rain and wind.
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10. Asexual Reproduction
• It reproduces asexually by spores called conidia.
• Conidia are single-celled, uninucleate, and narrower at one end
than the other.
• Conidia are produced by specialized short hyphae called
conidiophores.
• Conidiophores are formed on a dense mat of mycelia that pushes
up through and ruptures the leaf cuticle.
• The mass of conidia and conidiophores causes the velvety
appearance of young scab lesions.
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11. Cont…
• Conidia are produced nine to thirty days after initial leaf infection,
depending upon temperature.
• They are disseminated by wind and by wind-driven rain.
• Both ascospores and conidia require a period of wetness in order to
germinate.
• The germination hypha penetrates the cuticle and establishes a new
infection.
• There can be many cycles of conidial production and infection within
a single growing season.
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12. Figure 6. Conidia are asexual,
single-celled spores
Fig 7.Cross section through a leaf
infected with apple scab. Arrow
indicates the leaf cuticle, which
has been ruptured and pushed
back by the mass of erupting
conidia and conidiophores.
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14. Disease Management
1.Contact fungicides require
complete, uniform coverage. Leaf
appears to
be completely covered with residue.
2.An air blast sprayer being used to
apply fungicides in a commercial
orchard.
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15. Apple blossoms
• Blossom infections usually develop into small, dark green
lesions at the base of flowers, on sepals, and on stem pedicels
before and during bloom.
• Developing fruit may drop from infected pedicels, resulting in
lower fruit yield.
• Reduced and late-return bloom can result from infections that
had occurred in preceding years.
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16. Biological Control
• Scab-resistant or more appropriately scab-tolerant apples and
crabapples are widely available.
• Susceptible cultivars are still widely grown due to popularity and
consumer demand.
• cab-resistant flowering crabapples provide greater bloom
potential because there is no risk for defoliation.
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17. Importance
• The disease can reduce the quality and size of fruit.
• It can also cause premature fruit drop, defoliation and poor development of
fruit buds in the next season.
• Under favourable conditions and without control measures, apple scab can
cause total crop failure.
• The disease can cause high crop losses and is thus of economic import to
apple growers.
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18. Conclusion
• Apple scab is the most economically damaging pathogen in temperate and
humid apple-producing regions worldwide. Management of this disease is
essential to provide increased and sustainable apple production throughout
the world. The apple scab fungus has several host-specific strains that can
cause disease on one type of plant but not any other.
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19. References
• Beckerman, J. 2009. Managing scab-resistant apples (BP-76-W). Purdue University. Purdue Extension
Education Store. Available for download from: https://edustore.purdue.edu/
• Fungicide Resistance Action Committee. www.frac.info.
• Gessler, C., and Pertot, I. 2012. Vf scab resistance of Malus in: Trees (2012) 26:95. Doi 10.1007/s00468-
011-0618-y.
• Jones, A. L., Lillevik, S. L., Fisher, P. D. and Stebbins, T. C. 1980. A microcomputer-based instrument to
predict primary apple scab infection periods. Plant Dis. 64:69-72.
• Merwin, I. A., Brown, S. K., Rosenberger, D. A., Cooley, D. R., and Berkett, L.P. 1994. Scab-resistant apples
for the Northeastern United States: New prospects and old problems. Plant Disease 78:4-10.
• MacHardy, W. E. 1996. Apple Scab Biology, Epidemiology, and Management. APS Press St. Paul 545 pp.
• MacHardy, W. E. and Gadoury, D. M. 1989. A revision of Mills’ criteria for predicting apple scab infection
periods. Phytopathology 79:304-301.
• Morton, V., and Staub, T. 2008. A short history of fungicides. Online. APSnet Features. Doi
10.1094/APSnetFeature-2008-0308.
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