Question

Late blight of potato is caused by ______ that belongs to class ______.
a. Phytophthora infestans, Oomycetes
b. Helminthosporium oryzae, Deuteromycetes
c. Alternaria solani, Deuteromycetes
d. Albugo candida, Oomycetes

Answer 1

Hint: Late blight of potato is caused by a pathogen in moist, cool environments. Late blight infection of tubers is characterized by irregularly shaped, slightly depressed areas that can vary considerably from brown to purplish of variable size on the skin of the potato.

Complete Answer:
Phytophthora infestans, a fungus like oomycete, causes late blight in potatoes. This potentially devastating disease infects potato foliage and tubers at any stage of crop development. Late blight first appears as water-soaked spots, usually at the tips or edges of lower leaves where water or dew tends to collect. Under moist and cool conditions, these water-soaked spots rapidly enlarge into a broad yellow halo surrounding the lesion. On the underside of the leaf, a spore-producing zone of white moldy growth, approximately 0.1 - 0.2 inches wide, appears at the border of the lesion. If wet conditions persist, the disease progresses rapidly. Disease development ceases under warm, dry weather. A tan to reddish-brown, dry, granular rot is found under the skin in the discoloured areas which extends into the tuber.
P. infestans, the cause of late blight, is a heterothallic fungal-like pathogen, i.e., they require two mating types for sexual reproduction. Those types are referred to as A1 and A2. The pathogen is an obligate parasite that cannot survive without a living host. Infected potato tubers are the primary source of inoculum (fungus spores) for P. infestans. Potatoes in storage, infected tubers missed during harvest that remain unfrozen during the winter (volunteers), seed tubers and infected cull piles, and P. infestans on other host plants are the sources of the initiation of the disease. The pathogen can be transmitted from infected seed tubers to newly emerging potato plants, where it produces airborne spores that can move to neighbouring plants.

Note:
Night temperatures of 50 to 60 F and day temperatures of 60 to 70 F are most favourable for late blight development. Free water from rain, dew and overhead irrigation sprinkler irrigation all provide the water necessary for pathogen infection and development. Fungicides that contain maneb, mancozeb, chlorothalonil, or fixed copper can help protect plants from late tomato blight.