Late Blight of Potato
Causal Organism:
Name: Phytophthora infestans
Type: Oomycete (water mold)
Classification of Causal Organism :
Kingdom: Fungi
Division: Eumycota
Subdivision: Mastigomycotina
Class: Oomycetes
Order: Peronosporales
Family: Phthiaceae
Genus: Phytophthora
Species: infestans
Symptoms:
1. Foliar Symptoms:
Initial appearance of watersoaked lesions on leaves.
Lesions expand rapidly, turning dark brown to black and often surrounded by a pale green to yellowish halo.
Under humid conditions, a white, downy mildew (sporangia and sporangiophores) appears on the underside of leaves, especially at lesion margins.
Leaf tissue eventually collapses, leading to widespread defoliation.
2. Stem Symptoms:
Dark brown to black lesions may develop on stems and petioles.
Infected stems may collapse and die.
3. Tuber Symptoms:
Infected tubers show irregular, sunken, and reddish-brown to purplish lesions on the surface.
When cut open, tuber flesh underneath the lesions appears granular and rusty brown.
Secondary bacterial infections can occur, leading to soft rot and a foul odor.
Etiology:
Pathogen Characteristics:
Phytophthora infestans is a heterothallic oomycete, requiring two mating types (A1 and A2) for sexual reproduction, though asexual reproduction via sporangia is common.
Sporangia can germinate directly or indirectly by releasing zoospores, which are motile and can infect host tissues.
The pathogen thrives in cool, wet conditions, with an optimal temperature range of 1525°C (5977°F) and high relative humidity.
Disease Cycle:
1. Overwintering:
The pathogen survives in infected tubers (volunteer potatoes or cull piles) and in soil as oospores (if both mating types are present).
2. Primary Infection:
Infected seed tubers or volunteer plants provide the initial inoculum.
Sporangia produced on infected tissues are dispersed by wind, rain splash, or mechanical means to healthy plants.
3. Secondary Infection:
Sporangia land on susceptible leaf surfaces, germinate, and infect plant tissues.
Under favorable conditions, lesions develop rapidly, producing new sporangia and continuing the cycle.
4. Tuber Infection:
Sporangia washed from infected foliage into the soil can infect tubers directly through lenticels or wounds.
Harvesting and storage can further spread the pathogen if tubers are wet and handled roughly.
Management:
1. Cultural Practices:
Use of Certified Seed: Plant only disease free, certified seed tubers.
Crop Rotation: Avoid planting potatoes or related crops (e.g., tomatoes) in the same field for consecutive years.
Destroy Volunteer Plants: Remove volunteer potato plants and cull piles that can harbor the pathogen.
Proper Irrigation: Use irrigation practices that minimize leaf wetness periods, such as drip irrigation.
Hilling: Proper hilling of soil around plants can reduce tuber infection by sporangia washed from foliage.
2. Resistant Varieties:
Plant late blight resistant potato varieties when available like kufri Naveen, kufri moti etc.
3. Chemical Control:
Fungicides: Apply fungicides preventatively and according to local recommendations. Common fungicides include chlorothalonil, mancozeb, and systemic fungicides like metalaxyl and fluazinam.
Application Timing: Begin applications early in the growing season and continue at recommended intervals, especially during periods of high risk (cool, wet weather).
4. Biological Control:
Use of biocontrol agents such as Bacillus subtilis and Trichoderma spp. can provide some protection.
5. Sanitation:
Clean equipment and storage facilities to prevent the spread of the pathogen.
Dispose of infected plant debris properly to reduce the inoculum source.
6. Monitoring and Forecasting:
Regularly scout fields for symptoms of late blight.
Early Blight of Potato
Causal Organism:
Name: Alternaria solani
Type: Fungal pathogen
Symptoms:
1. Foliar Symptoms:
Small, dark brown to black lesions initially appear on older leaves, typically on the lower parts of the plant.
Lesions expand and become circular to irregular, often with concentric rings giving a "target spot" appearance.
Surrounding tissue may yellow and die, leading to a blighted appearance.
Severe infections cause defoliation, starting from the bottom and progressing upward.
2. Stem Symptoms:
Dark, elongated lesions can develop on stems, petioles, and leaf veins, leading to girdling and weakening of the affected parts.
In severe cases, stems may become brittle and break.
3. Tuber Symptoms:
Dark, sunken, circular to irregular lesions on the surface of tubers.
Underneath these lesions, the tuber tissue becomes corky and dry, often leading to secondary bacterial infections.
Etiology:
Pathogen Characteristics:
Alternaria solani produces conidia (spores) that are typically spread by wind, rain splash, and mechanical means.
The fungus thrives in warm, humid conditions, with an optimal temperature range of 2429°C (7585°F).
High humidity and leaf wetness facilitate spore germination and infection.
Disease Cycle:
1. Overwintering:
It can persist in the soil for several years, contributing to the inoculum load for future crops.
2. Primary Infection:
Initial infections often arise from soil borne spores or debris borne inoculum that infect the lower leaves of the plant.
Spores can also be introduced with infected seed tubers.
3. Secondary Infection:
Secondary cycles of infection occur as spores produced on infected leaves and stems are dispersed to healthy tissues by wind and rain.
The pathogen can infect any aboveground part of the plant during the growing season.
4. Tuber Infection:
Infection of tubers occurs mainly through wounds or natural openings such as lenticels, especially during harvest when tubers are exposed to spores in the soil.
Management:
1. Cultural Practices:
Crop Rotation: Avoid planting potatoes or other Solanaceous crops in the same field for consecutive years to reduce inoculum buildup.
Field Sanitation: Remove and destroy infected plant debris after harvest.
Proper Irrigation: Use irrigation practices that minimize leaf wetness periods, such as drip irrigation, and avoid overhead irrigation late in the day.
Adequate Spacing: Ensure proper plant spacing to improve air circulation and reduce humidity within the canopy.
2. Resistant Varieties:
Plant early blight resistant potato varieties when available.
3. Chemical Control:
Fungicides: Apply fungicides preventatively and according to local recommendations. Common fungicides include chlorothalonil, mancozeb, and azoxystrobin.
Application Timing: Begin applications early in the growing season and continue at recommended intervals, especially during periods of high humidity and moderate temperatures.
4. Biological Control:
Use of biocontrol agents such as Bacillus subtilis and Trichoderma spp. can provide some protection.
5. Nutrient Management:
Maintain balanced fertility to ensure healthy, vigorous plants that are less susceptible to infection.
Avoid excessive nitrogen fertilization, which can promote lush, susceptible foliage.
6. Seed Management:
Use certified disease-free seed tubers.
Treat seed tubers with appropriate fungicides before planting to reduce the risk of introducing the pathogen.
7. Monitoring and Forecasting:
Regularly scout fields for symptoms of early blight.
Utilize disease forecasting models and weather monitoring systems to predict high-risk periods and time fungicide applications effectively.
Mosaic Disease of Potato
Causal Organisms:
Mosaic disease of potato is caused by a group of viruses, the most common being:
1. Potato Virus Y (PVY):
Family: Potyviridae
Genus: Potyvirus
2. Potato Leafroll Virus (PLRV):
Family: Luteoviridae
Genus: Polerovirus
Symptoms:
1. Potato Virus Y (PVY):
Mosaic Patterns: Light and dark green mosaic patterns on leaves.
Leaf Curling: Downward leaf curling and slight rolling.
Stunting: Reduced plant height and overall stunted growth.
Necrotic Spots: Development of necrotic spots and streaks on leaves, stems, and tubers in severe cases.
2. Potato Leafroll Virus (PLRV):
Leaf Rolling: Upward rolling of leaf margins, giving the plant a "rolled" appearance.
Yellowing: Yellowing or chlorosis of leaf margins and interveinal areas.
Stunting: Severe stunting of the plant.
Tuber Symptoms: Net necrosis inside the tubers, leading to brown streaks and reduced tuber quality.
Etiology:
1. Potato Virus Y (PVY):
Transmission: Primarily transmitted by aphids, particularly the green peach aphid (Myzus persicae).
Survival: PVY can survive in infected tubers, volunteer plants, and certain weed hosts.
2. Potato Leafroll Virus (PLRV):
Transmission: Transmitted by aphids in a persistent manner, meaning the virus remains in the aphid for a long time and can be spread over several days.
Survival: PLRV also survives in infected tubers and volunteer plants.
Disease Cycle:
1. Primary Infection:
Infected seed tubers are the main source of primary infection. When these tubers sprout, they produce infected plants, which serve as a source of virus for aphids.
2. Secondary Infection:
Aphids acquire the virus from infected plants and transmit it to healthy plants as they feed.
Secondary spread continues as long as aphids are active and temperatures are conducive to their activity.
3. Overwintering:
The viruses overwinter in infected tubers and volunteer potato plants left in the field.
Weeds and other solanaceous hosts can serve as reservoirs for the viruses.
Management:
1. Cultural Practices:
Use Certified Seed Tubers: Plant virus free certified seed tubers to prevent primary infection.
Rogueing: Remove and destroy infected plants early in the season to reduce virus spread.
Volunteer Control: Eliminate volunteer potato plants and weeds that can act as virus reservoirs.
2. Vector Control:
Aphid Management: Implement aphid control measures using insecticides and aphid resistant crop varieties.
Reflective Mulches: Use reflective mulches to deter aphids from landing on plants.
Oil Sprays: Apply mineral oils to plants to reduce virus transmission by aphids.
3. Crop Rotation:
Rotate potatoes with non host crops to reduce the buildup of virus inoculum in the soil and surrounding vegetation.
4. Resistance:
Plant potato varieties that are resistant or tolerant to PVY and PLRV.
Use resistant rootstocks for grafting if available.
5. Chemical Control:
Apply systemic insecticides to control aphid populations effectively.
Use antitranspirants to reduce aphid feeding and virus spread.
6. Monitoring and Forecasting:
Regularly monitor aphid populations and virus symptoms in the field.
Use virus indexing and diagnostic tests to detect and manage virus infections early.
Black Heart of Potato Disease
Causal Organism Name
Black heart of potato is not caused by a pathogen like a bacterium, fungus, or virus. Instead,it is a physiological disorder primarily due to environmental conditions such as low oxygen levels.
Symptoms :
Internal Browning:
External Appearance:
The exterior of the potato usually looks normal, making it difficult to detect the disorder without cutting the tuber open.
Texture:
Affected areas may become dry and corky, though in some cases the texture remains relatively unchanged until the advanced stages.
Etiology
Black heart occurs when potato tubers are subjected to low oxygen conditions. This can happen under several circumstances:
Poor Storage Conditions: When potatoes are stored in environments with insufficient ventilation or at temperatures that promote low oxygen availability (usually below 4°C or above 30°C).
High Temperature: Exposure to high temperatures, particularly during storage or transport, can exacerbate the condition as metabolic activity increases, consuming available oxygen rapidly.
Piling: Storing potatoes in large piles can restrict airflow, leading to localized low oxygen areas within the pile.
Disease Cycle
Since black heart is a physiological disorder rather than a disease caused by an organism, it does not have a traditional disease cycle. However, the development can be understood in stages:
1. Initiation: Begins when potatoes are exposed to low oxygen conditions.
2. Progression: The center of the potato becomes oxygendeprived, leading to cell death and blackening.
3. Manifestation: Over time, the blackened area enlarges as more cells die from the lack of oxygen.
4. Detection: Typically noticed when potatoes are cut open for consumption or processing.
Management
Managing black heart involves primarily prevention through proper handling and storage:
1. Storage Conditions:
Temperature: Store potatoes at a temperature range of 410°C (4050°F). Avoid temperatures below 4°C, which can cause chilling injury, and above 30°C, which can increase respiration rates.
Ventilation: Ensure good ventilation in storage facilities to maintain adequate oxygen levels.
2. Piling:
Avoid storing potatoes in large piles. Instead, use crates or bins that allow for better air circulation.
3. Handling:
Minimize mechanical injury during harvesting and handling as damaged potatoes are more susceptible to black heart.
4. Transport:
During transport, ensure the potatoes are not subjected to high temperatures or conditions that could lead to low oxygen availability.
By carefully managing storage conditions and handling practices, the incidence of black heart in potato tubers can be significantly reduced.