Late blight of potato is caused by the fungus Phytophthora infestans. It initially infects the lower leaves and can attack the plant at any time after foliage develops. The disease leads to water soaked spots on leaves that turn purple-brown and black, and white growth develops on the underside of leaves. It also causes purplish brown spots on tubers. Cool, humid conditions favor the spread of the disease. Control measures include using resistant varieties, avoiding bruising of tubers, and regularly spraying fungicides like mancozeb every 10-15 days during crop growth.

2. Late Blight of Potato

3. Late Blight of Potato
Description:
• This disease caused by fungus called Phytophthora
infestans.
• The disease may attack almost any time after the crop has
put up a fairly good foliage.
• Initially the lower leaves infected.

5. Late blight
Phytophthora infestans
• Irish famine - 1845-46
Symptoms
• Leaves, stems and tubers
• Water soaked spots appear on leaves, turn purple brown & finally
black colour
• White growth develops on under surface
• Stem breaks at these points and the plant topples

6. • In tubers - purplish brown spots & spread to
entire surface
• Tuber show rusty brown necrosis spreading
from surface to the center

10. Mode of spread and survival
• Infected tubers and infected soil - source of primary infection
• Survival of fungus in fruiting stage or as dormant mycelium
in the soil
• Persisting of perennial mycelium in affected tubers from the
field, stored and used as seed in next season
Epidemiology
• Cool (12 to 15oC) and humid ( above 90 %) weather with
rains alternating with warm (20o C) moist period

11. Fungus
 Mycelium - endophytic, coenocytic and hyaline
 Sporangiophores – arise from internal mycelium through stomata
on the tubers
 Sporangia - multinucleate, thin walled, hyaline, oval shaped
 Zoospores - biflagellate
Phytophthora infestans
A, zoospores produced within the
lemon-shaped sporangia (B).

15. Control measures
 S. demissum and S. phureja - used for breeding for disease
resistant varieties
 Varieties - Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Moti
 Bruising of tubers at harvest should be avoided
 Regular spraying during growing season gives effective control- 10
to 15 days interval
– Brestan 600g/ha
– Zineb 0.2 %
– Bordeaux mixture 1.0%
– Mancozeb (2 kg/ha)