Potato diseases description

Introduction
• Potato is an important crop which its production is
hampered by many fungal diseases (Uwamahoro et al.,
2018).
• Some of the major fungal diseases include: late blight,
early blight, black scurf, fusarial wilt/dry rot, wart,
powdery scab, and charcoal rot (Obidiegwu, Flath and
Gebhardt, 2014).
• Brief description, impacts, distribution and control
measures for black scurf, wart as well as charcoal rot
disease will be discussed in below context.

1. Black scurf on potato
Common name
• Rhizoctonia damping off, blight and rot, white blight,
Target spot, Rhizoctonia canker.
• This disease is present in all potato-growing areas.
a) Causal organism
• Rhizoctonia solani ( Anamorph)-Kuhn.
• Thanatephorus cucumeris(Teleomorph)-A.B Frank Donk.

1.Black scurf on potato…..
• In 1858, Julius Kuhn observed and described a
fungus on diseased potato tubers and named it
R.solani.
• Rhizoctonia is Greek word.
Rhiza means root and
Ktonos means murder.
• Solanum is the latin word it means night shade.

• Hussain et al., (2012) succeeded to isolate the bluckscurf
organism from the potato crop.

b)Taxonomy
• Kingdom: Fungi
• Phylum: Basidiomycota
• Class: Agaricomycetes
• Order: Ceratobasidiales
• Family: Ceratobasiaceae
• Genus: Rhizoctonia
• Species: R.solani

c) Symptoms per phenological stages
and physiological change
Black scurf is induced at the phase of tuberization. of stem
canker. Infection by the seed and soil-borne fungus leads to
the development of black scurf on tubers at the end of the
growing season and during storage(El Bakali et al., 2006).
1. Black scurf on tubers: On the skin there is dark, crust- like
structure. It is developed after haulm killing and continue
during storage.

1. Black scurf on potato…..
2. Damaged young sprouts, poor crop: The are
distinct sunken lesions on the young sprouts,
reddish-brown to grey.

3. White fungus sheets and lesions on stems and stolon: The
reddish-brown to brown lesion is formed at the base of the
stems and stolon. The low part contacting near the soil, the
white fungus is observed (Tseror at al., 2005).
.

4.Tuber formation near the stem and nests of small,
deformed tubers

5.Stunting and resetting of plant tops

6. Aerial tubers: The interference of carbohydrates
movement cause the formation of aerial tubers in the leaf
axils of stems.

7. Scab-like lesion on tubers, deformed and eyeless tubers,
dry core symptoms:

E) The impact and yield loss
• The rhizoctonia solani cause the considerable damages to
the crop. After emergence infected sprouts may die and as
a consequence crop stand will be poor (Tseror et al., 2005).
• The significant loss in yield reduction is based on the stage
of the disease.
• Some of these consequences are major yield losses from
25% to 100%(Wharton et al., 2007). .

F) Geographical distribution and control
• The rhizoctonia solani can be found across areas of world
wide but the united states is the particular case of this
fungus (Wharton et al., 2007)..
E) The control
 Planting screlotia free seed potatoes
 Rhizoctonia free fields, crop rotation
 Treating seed potatoes with fungicides
 Biological control agents like V. biguttatum, Trichoderma
harzianum have been successful to suppress R. solani.

2. Potato Wart (Synchytrium endobioticum)

2. Potato wart (Synchytrium endobioticum)
• Wart occurs in Africa, Asia, New Zealand, Europe,
North and South America (Franc, 2007).
• It caused great damage to potato in Europe until
immune varieties were introduced (Przetakiewicz J,
2008).

2. Potato wart (Synchytrium…
• According to Van den Boogert et al., (2005). , the isolation
of wart (Synchytrium endobioticum) sporangia from
potato flesh and dry tissues occurred.
• Using the light microscope, the resting spores were seen.

a) Disease Causative Agent
• Wart is caused by Synchytriun endobioticum (discovered
by Schilberszky from Budapest University) which is an
obligate parasite with at least 10 pathogenic races in the
member of chytridales (Van den Boogert et al., 2005).
• Both summer and winter sporangia produce an extended
vesicle called sorus from where zoospores are produced.

b) Taxonomy
Kingdom: Fungi
Division: Chytriodiomycota
Class: Chytridiomycetes
Order: Synchytriales
Family: Synchytriaceae
Genus: Synchytrium
Species: s. endobioticum

c) Symptoms per phenological stages
S. endobioticum sporangia persist so long in soil that it attacks
the potato at tuberization stage (Wale et al., 2008).
• Rough warty mostly spherical outgrowths or protuberances
appear on buds and eyes of tubers, stolons, or underground
stems or at stem base (Franc, 2007).
• Wart may appear occasionally on above ground stem, leaf or
flowers.
• . Underground galls are white to light pink when young and
turn brown or light black with age.
• Above the ground galls are green to brown or black.
(Obidiegwu et al., 2014)

d) Impacts and yield loss
• The tumors progressively increase in size at the
expense of tubers, resulting in yield losses in the
range of 50–100 % (Franc, 2007).
• The major agricultural problem is the
contamination of soil with persistent resting spores
that remain infectious for more than 20 years
(Obidiegwu et al., 2014).

E) Geographical distribution
• The origin of S. endobioticum is in the Andean
mountains of Latin America, where it co-evolved
with potato (Przetakiewicz,2008).
• It is assumed that S. endobioticum spread at the
end of the nineteenth century from the center of
origin in the Andes first to Europe and North
America, and subsequently across the whole potato
growing regions of Asia, Africa and Oceania
(PrzetakiewiczJ, 2008).

F) Control
Mere cultivation of wart immune varieties.
The sanitation, long crop rotation.
Intercropping potato with maize, or growing
rotational crops such as bean and radish has been
found to reduce pathogen population (viable
resting spores) in soil (Arora and Khurana, 2006).

3.Charcoal rot (Macrophomina phaseolina)

3.Charcoal rot (Macrophomina…
• Charcoal rot is also an important disease of many
vegetable crops in tropical and subtropical countries
where high soil moisture is coupled with temperature
exceeding 28oC (Gupta et al., 2002 & Somani, 2013 &
Obidiegwu et al., 2014).

A) Causal agent
• Charcoal rot of potato is caused by fungus
Macrophomina phaseolina (Somani,2013).
• Black, smooth, hard 0.1 to 1.0 mm sized sclerotia of the
fungus develop within roots, stems, tubers and leaves.

• The colony appears grayish white, turning gray and
becoming blackish mouse gray at maturity as well as
young advancing hyphae are full of granular contents
(Mengistu et al., 2007).
• Older hyphae appear brownish gray to deep brown with
snuff brown walls.

B)Taxonomy

C) Symptoms per phenological stages
• Tubers are infected first at the eyes. Potatoes with charcoal
rot will display signs and symptoms at harvest (Yang et al.,
2005). Water soaked gray lesions appear that slowly turn
black.
• Infected stems develop a soft, dark rot similar to blackleg
(Gupta et al., 2002).

• Early symptoms on tubers develop around eyes,
lenticels and stolon end where a dark light grey, soft,
water soaked lesion develops on the surface. Cavity
within the lesion becomes filled with black mycelium
and sclerotia of the pathogen (Gupta et al., 2002).

3. Charcoal rot (Macrophomina…
d)Impacts/yield loss
• M. phaseolina is a weekly parasitic soil fungus and
over winters in soil as sclerotia in plant debris, weeds
and alternate host crops. Both soil and infected tubers
serve as source of inoculum (Somani, 2008).
• When severe, charcoal rot reduces yield of 42% and
seed quality (Mengistu et al., 2011).

E)Geographical distribution
• This disease occurs in tropical and subtropical
countries where high soil moisture is coupled with
temperature exceeding 28oC (Wale et al., 2008).
• It is of major importance in the Mediterranean
region, Hawaii, Southern United States of America,
warmer areas of Peru and India (Obidiegwu et al.,
2014).

F) Control
• Plant the charcoal rot immune varieties
• Planting early maturing cultivars because this
fungus has crucial development in the harvesting
period where the soil increases in temperature of
280C.
• Bio-control using Bacillus subtilis through seed
treatment has been reported to reduce incidence
of charcoal rot (Obidiegwu et al., 2014).

Conclusion
• Potato holds the promise for food to millions of
people especially in developing countries. Full
potential of the crop can be realized only if diseases
and pests are kept under control.

Potato diseases description

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