Early Blight of Potato: Cause, Symptoms, Disease Cycle and Management
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What is Early Blight of Potato?
Early Blight of Potato is very common disease of potato wherever potato is grown. The attack of the disease can be seen in each potato growing country.
Also, it is a very common disease of potato in India. And, it is more common than the late blight of potato in India.
The occurrence of the disease can be seen few weeks after sowing the tubers. But, the damage to the crop is more during the tuber formation.
The disease can be seen both in the cool and warm areas. Farmers of hills and plains, both face this serious disease.
Also read: Plant pathology multiple choice objective questions
1. The Cause of The Disease
The causal organism of early blight is a fungus. The pathogen is Alternaria solani (Ell. and Martin) Jones and Grout. These are mitosporic fungi with no s_xual stage.
Characteristics of the Casual Organism
1. Inter-cellular Mycelium: The inter-cellular mycelium of Alternaria solani consists of septate and branched hyphae.
2. Intra-cellular Mycelium: The intera-cellular mycelium of Alternaria solani also consists of septate and branched hyphae.
3. Intercalary Cells: The intercalary cells contain less numbers of nuclei than the tip cells.
4. Conidiophore: Conidiophore emerge through stomata. Conidiophore are relatively short (50 – 90 × 9 μm) having dark colour.
5. Conidia: The size of conidia is larger than the conidiophore. It is beaked and muriform. They are borne singly on the conidiophores. 5 – 10 septa are present in each conidium.
6. Melanin: Melanins have high molecular weight.
7. Strains: At leat 3 strains are present in India.
Also read: Mycoplasma diseases of vegetable crops
2. Life Cycle
Hosts: Potato, tomato, chilli, brinjal etc.
The fungus remains viable in infected leaves for many years.
Conidia and mycelium survive in the soil on plant debris to cause primary infection to next crop. Contaminated tubers also act as a source of primary infection.
Infection: Infection occurs first in lower leaves.
Penetration: Through stomata, through cuticle, wound.
Secondary infection occurs through conidia on primary spots. These conidia are disseminated by wind, rains and insects.
Incubation Period: 48 – 72 hours.
3. Symptoms of Damage
The leaves near the soil surface are attacked first and progresses upward.
Symptoms on Leaves: The disease can be seen as small, scattered, pale brown spots on the leaflets. These spots are covered with growth of the fungus.
Necrotic Area: There is a necrotic area. In the necrotic area of the spots concentric ridges develop to produce a characteristics board effect.
Target Board: ‘Target Board’ is the most characteristics symptom of early blight of potato.
Vein Chlorosis: Later, vein chlorosis may also occur.
Curling of Leaves: In dry weather the spots turn hard and the leaves curling can be seen.
Rotting of Leaves: In humid weather big totting patches appear on leaf surface.
Severe Attack: Leaves shrivel and fall off. Stems show brown to black necrotic lesions on the skin. Rotten plant may collapse.
4. Management of The Disease
Don’t sow the tubers of potato in the same field every year. Try different crop of different family.
Field sanitation is very necessary. It is a before and after harvesting practice.
Burning the Debris
It is very necessary to burn the plant debris, so burn the lant debris immediately after drying.
Application of Fungicide
Spray the right fungicide at right time. Give first spray one month after planting. Spray should be done throughout the period of the plant growth.
The interval of spray should be 10 – 21 days. Use Zineb (0.2%) as fungicide.
“The strobilurin fungicides (azoxystrobin and trifloxystrobin and pyraclostrobin) have also been used”. (Ref. 02).
Some Important Points
1. Up to 40% or more than the 40% loss in potato yield (potato tubers). So it is a very harmful disease.
2. The casual organism (Alternaria species) produces: 1. Production of melanin in spore. 2. Production of host-specific toxins in the case of pathogenic species.
3. The hyphae in the host are at first intercellular.
4. The hyphae in the host later penetrate the cells.
5. The fungus produces chlamydospores also.
6. Penetration occurs most frequently through the junction of epidermal cell. The number of penetration sites with HR is higher in the upper part of the plant. (Ref. 01).
F A Q
Questions 01. Generally, this pathogen attacks on potato, what are the other crops?
Answer: Apart from potato, this pathogen attacks tomato and chilli. Loss is significant.
01. Dita, M.A. et al., 2007. Histopathological studies of the Alternaria solani infection process in potato cultivars with different levels of early blight resistance. J. Phytopathol. 155(7-8): 462.
02. Pasche, J. S., C.M. Wharam and N.C. Gudmestad, 2004. Shift in sensitivity of Alternaria solani in response to Q(o) fungicides. Plant Dis. 88 (2): 181.