Early blight of potatoes

1. POTATO
 A member of the Solanaceae family, the cultivated
potato (Solanum tuberosum) is closely related to
the tomato, pepper, and eggplant.
 Indians in Peru were the first people to cultivate
the potato over 4000 years ago
 The potato, a name derived from the American
Indian word "Batata", was introduced to
Europeans be Spanish conquerors during the late
16th Century
 A potato is about 80% water and 20% solid.
 The average American eats 140 pounds of
potatoes per year. Germans eat more than 200
pounds per year.

2. Nutritional value per 100 g
Carbohydrates 19 g
Starch 15 g
Dietary fiber 2.2 g
Fat 0.1 g
Protein 2 g
Water 75 g
Thiamin (Vit. B1) 6%
Riboflavin (Vit. B2) 2%
Niacin (Vit. B3) 7%
Vitamin B6 19%
Vitamin C 33%
Calcium 1%
Iron 14%
Magnesium 6%
Phosphorus 8%
Potassium 9%
Sodium 0%

3. EARLY BLIGHT OF POTATO
 Symptoms:
 The initial symptoms appear in the form of small,
isolated scattered pale brown spots on leaves with
deep greenish-blue fungal growth of fungus. The
lower leaves are attacked first and then the disease
progresses upwards.
 In the necrotic tissue, concentric ridges develop,
which give a target board effect.
 The stem lesions often girdle it and cause “Collar-rot”
in young seedling plants leading to collapse of
branches or entire above ground portion.
 On tubers the affected region is darker than the
healthy area and the lesion soon shrinks slightly as
dry, corky rot develops.

7. Causal organism: Alternaria solani
 Disease Cycle:
 Mycelium and conidia can survive in plant
debris and on seed tubers.
 The conidia germinate in moist weather
and cause primary infection directly or
through stomata, first on lower and then
on upper leaves.
 The secondary infection takes place
through conidia carried by wind, water or
insects.

8. Epidemiology
 The optimum temperature for conidial
germination is 28-30ºC.
 If season starts with abundant moisture
and frequent rains, disease becomes
serious, followed by warm and dry weather,
which is unfavourable for the host but
helps rapid disease development. Weaker
plants are more susceptible.

9. CONTROL
 Crop rotation and field sanitation is a rational
measure to avoid primary infection from spores
that have survived from previous crop.
 Fungicidal sprays starting from 30 days after
sowing at an interval of 10-21 days (depending
upon the intensity of disease). For this purpose,
Dithane M-45 (0.6%), Daconil (0.3%), Acrobat
MZ, Ridomil Gold MZ, Banko (0.2 – 0.25%) can
be used.
 Proper fertilization of the crop to maintain the
plant vigour

10. LATE BLIGHT OF POTATO
 The disease was recorded simultaneously in
Europe and North America in 1830. It became
very well established in Europe by 1842 and was
one of the important causes of the great Irish
famine in 1845 and 1846.
 It invaded the sub-continent between 1870 and
1880. This is extremely destructive to tomato
and eggplant and many other solanaceous hosts
except pepper.
 It may bring about as much as 10-15 percent
losses to world production of potatoes during
certain years.

11. SYMPTOMS
 The first symptoms appear in the form of brown dead
spots or extended necrotic areas more frequently until
the leaves are killed.
 These blighted areas first appear as faded green
patches, which soon turn to brownish black lesions
not delimited in size. These lesions enlarge rapidly
under favourable weather.
 They appear on tips of margins of the leaves and
spread downwards or inwards. In moist weather, entire
leaf may be killed in 1-4 days..
 On lower surface of leaves, a whitish or grayish mildew
growth appears on the surface of lesions where pale
and purplish tissues merge. This contains
sporangiophores and sporangia, which grow out
through stomata.

14. Causal organism: Phytophthora infestans
 Disease Cycle:
 Fungus survives mostly as persistent mycelium in
the infected tubers, but it may overwinter in soil as
well. This mycelium grows up in the stem and
produces sporangia and zoospores on small dwarf
shoots.
 The secondary infection starts from these spores.
Infection takes place epidermis of leaves and stem
either through stomata or directly.
 Tuber infection occurs through eyes, lenticels or
wounds. Susceptibility of eyes and resistance of
lenticels increases with storage and maturity of
tubers. Spores from blighted leaves are washed
down to soil and cause tuber infection.

16. EPIDEMIOLOGY
 The favorable conditions for the blight, extended
periods of cool and wet weather, are explained by the
biology of the parasitizing fungus.
 Sporangia best survive dispersal by air when the air
is humid, and water is necessary for infection by the
fungus.
 In addition, zoospores are produced at cooler
temperatures, which maximizes the number of
potential infections possible from a single
sporangium Germination and infection always require
water on the leaf surface.
 At higher temperatures (over 68°F or 20°C), the
sporangia germinate by producing a single
germination tube rather than zoospores.
 Thus, the number of potential infections from a single
sporangium is greatly reduced in warmer
environments, although disease is not eliminated.

17. MANAGEMENT
 Dispose of cull potatoes and seed chips properly by
burying to a depth of 2 feet before any potatoes emerge in
the spring.
 Control volunteer potato plants as they emerge.
 Plant certified seed that is free of late blight (from late-
blight-free production areas).
 Do not over-irrigate. Monitor irrigations carefully.
 Do not irrigate when free moisture will stay on leaves for
an extended time, i.e. try to water during late night and
early morning so foliage can dry quickly during daytime
hours.
 Avoid having wet spots in fields.
 Shut off the inner two towers of center pivot systems.
 Apply protectant fungicides.
 Apply the protectant when foliage is 6" high and again
just before row closure.
 Apply additional fungicides according to the disease
risk.

18. Early Blight Late blight
High temperature and low
moisture is required
Reverse in this case
Appears early in season Reverse in this case
Appears in Plains Appears in Hilly areas
Caused by a higher fungus Caused by a lower
fungus