1. Potato crop Diseases, Symptoms, Etiology, Disease cycleand
Their Management.
: Alternaria solani
: Phytopthora infestans
: Rhizoctonia solani
: Potato leaf roll virus
1. Early blight
2. Late blight
3. Black scurf
4. Leaf roll
5. Mosaic :
a. Mild mosaic/Interveinal mosaic
b. Severe mosaic
c. Rugose mosaic of potato
: (Potato virus X) PV X
:Potato virus Y (PV Y)
: Potato virus X &Y
2. 1. Early blight : Alternaria solani
īą Symptoms:
īThis is a common disease of potato occurring on the foliage at any stage of
the growth and causes characteristic leaf spots and blight.
īNormally the disease symptoms become apparent during tuber bulking
stage and develop leading to the harvest.
īThe early blight is first observed on the plants as small, black lesions
mostly on the older foliage.
īSpots enlarge, and by the time they are one-fourth inch in diameter or
larger, concentric rings in a bull's eye pattern can be seen in the center of the
diseased area.
īTissue surrounding the spots may turn yellow. If high temperature and
humidity occur at this time, much of the foliage is killed.
īLesions on the stems are similar to those on leaves, sometimes girdling the
plant if they occur near the soil line.
3. īąEtiology:
īThe mycelium is septate, branched, light brown colour, spread
inter and intracelluar in the host tissue.
īThe conodiophore are short, light brown, septate arise from disease
tissue and emerge through stomata.
īThe conidia are borne in chain at tip of conidiophores. Conidia are
obclavate, muriform with 5-10transverse septa.
4. īąDisease Cycle/perpetuation of Early blight of disease:
īPrimary Infection: Mycelium or conidia in infected plant debris
īSecondary Infection: Conidia dispersed by wind, water or rain
splashes
īąManagement of early blight disease
īUse of disease free seed
ī Practicing crop rotation helps to minimize the disease incidence.
īRemoval and burning of diseased crop debris
īNursery spraying after 2 weeks after sowing with COC 50WP
īMancozeb@0.25% or chlorothalonil@0.2% or Zineb@ 0.25%spray at
weekly intervals.
īSpray Mancozeb + urea solution i.e. at the rate of 2 g Mancozeb 75
WP + 10 g urea per litre of water at 15 days interval when symptoms
start.
5. 2. LATE BLIGHT : PHYTOPTHORA
INFESTANS
īą Symptoms:
A. Symptoms on leaf
īThe first symptoms of late blight in the field are small, light to dark
green, circular to irregular-shaped water-soaked spots. These lesions
usually appear first on the lower leaves. Lesions often begin to develop
near the leaf tips or edges, where dew is retained the longest.
īDuring cool, moist weather, these lesions expand rapidly into large, dark
brown or black lesions, often appearing greasy. Leaf lesions also
frequently are surrounded by a yellow chlorotic halo
īThe lesions are not limited by leaf veins, and as new infections occur
and existing infections coalesce, entire leaves can become blighted and
killed within just a few days. The lesions also may be present on petioles
and stems of the plant.
īThe lesions are not limited by leaf veins, and as new infections occur
and existing infections coalesce, entire leaves can become blighted and
killed within just a few days. The lesions also may be present on petioles
and stems of the plant.
6. B. Symptoms on tubers:
īLate 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.
īA tan to reddish-brown, dry, granular rot is found under the skin in the
discolored areas and extending into the tuber usually less than ÂŊinch
7. īąEtiology:
īMycelium is coenocytic, hyaline, branched and both inter and intracelluar
īThe conidiophores are aerial and arise from the internal mycelium
through stomata
īand lenticel on the tubes. They are slender hyaline, branched and
indeterminate.
īThe sporangia are thin walled, hyaline, oval or pear shaped with a definite
papilla at the apex germinating by zoospore. Oospore are thick walled and
yellowish.
8. īąDisease cycle:
The infected tubers and the infected soil may serve as a source of
primary infection.
The diseased tubers are mainly responsible for persistence of the disease
from crop to crop.
The air borne infection is caused by the sporangia.
īąManagement:
īProtective spraying with mancozeb or zineb 0.2 %should be done to
prevent infection of tubers.
īTuber contamination is minimized if injuries are avoided at harvest
time and storing of visibly infected tubers before storage.
īThe resistant varities recommended for cultivation are Kufri Naveen,
Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo and Kufri Moti.
īDestruction of the foliage few days before harvest is beneficial and this
is accomplished by spraying with suitable herbicide
9. 3. BLACK SCURF : RHIZOCTONIA SOLANI
īą Symptoms
īSymptoms can be observed on above and below ground plant parts.
īSymptoms observed above ground early in the season include necrosis
at the tips of the sprouts (which may eventually cause the emerging
plant to die) and sunken lesions on stolons, roots, and stems.
īLater in the season, sclerotia are produced in the tubers creating a sign
called black scurf which is simply, sclerotized mycelium.
ī Stems with cankers can become girdled, resulting in stunted plants.
ī Leaves of infected plants develop a purplish and chlorotic coloration.
In severe infections, green tubers develop above the ground.
īAffected tubers are deformed and can produce sclerotia on the surface.
10. Tuber russet
Sunken leisons on stem
īąEtiology:
īRhizoctonia solani is a basidiomycete fungus that does not produce any asexual
spores (called conidia) and only occasionally will the fungus produce sexual spores
(basidiospores). In nature, R. solani reproduces asexually and exists primarily as
vegetative mycelium and/or sclerotia
īYoung mycelium of R Solani is silvery and become yellow to brown at maturity 8- 12
Âĩm in dia.
īHaving frequent septation and branched.
īSclerotia are dark brown to black.
īThey are roughly spherical or somewhat flattened or irregular, shape of micro
scleortia is oval to irregular
11. īąDisease Cycle
īP.I: Oospores (Pythium) or Sclerotia (Rhizoctonia) in soil
īS.I: Seedlings raised in infected soil carry the disease to field
īąManagement:
īDisease free seed tubers alone should be planted.
īIf there is a slight infection of black scurf that can be controlled by treating
seed tubers with mercuric chloride solution for 1.5 hr with acidulated
mercuric chloride solution for 5 min.
īTreating the soil with pentachloroni trobenzene at the rate of 70 kg/ ha
lowers the incidence of the disease, but it is too expensive and cumbersome.
īWell sprouted tubers may be planted shallow to control disease.
īThe disease severity is reduced in the land is left fallow for 2 years.
12. 4.Leaf roll : Potato leaf rollvirus
īą Symptoms:
īThe symptoms appear early and young leaves show an upward roll.
īLeaves become dry, leathery and thick. They turn brittle and give
their distinctive rattle when shaken.
īPlants may also be severely stunted, erect and light green.
īTubers are reduced in size and number. With some varieties, a net
necrosis develops inside the tuber.
13. īąTransmission
ī Infected tubers (Sap inoculation)
ī Spread by aphids, Myzus persicae and Aphis gossypii
īąManagement:
īDisease free seed tubers for planting.
īUse of disease free certified seed.
īRouging of diseased plants and burying them deep in soil.
īAphid control.(Phorate 10G ,10Kg/ha or monochrotophos).
14. : (Potato virus X) PV X
5.Mosaic :
a. Mild mosaic/Interveinal mosaic
īą Symptoms:
īOften referred as latent potato mosaic
ī Light yellow mottling with slight crinkling on potato plants
ī Interveinal necrosis of top foliage
ī Stunting of diseases plants
ī Leaves may appear slightly rugose where strains of PV Y combines
15. B) SEVERE MOSAIC â POTATO VIRUS Y (PV Y)
ALSO CALLED POTATO LEAF DROP STREAK
īąSymptoms
ī Chlorotic streaks on leaves which become necrotic
ī Necrosis of leaf veins and leaf drop streak
ī Interveinal necrosis and stem/petiole necrosis
ī Plant remain stunted in growth
īRugosity and twisting of the leaves occurs in combination with PV X
and PV A
16. C. Rogose and Common Mosaic : Potato virus X &Y
īąSymptoms
īBlack streaks appear in leaf veins and on stems.
īEarly-season infection shows shriveled leaves that hang from the stem
by a thread of dead tissue.
īLater in season, the plants become bare with a few leaves on top. Late-
season infection does not show any symptoms.
īPlants from infected seed tubers have mottled and wrinkled leaves that
are distorted ("rough") and reduced.
īStems are brittle and dwarfing is common. Harvested tuber size is
greatly reduced.
īThe primary pathogen is Potato Virus Y (PVY) which may act alone or
in conjunction with PVX. There are many strains of PVY with differing
characteristics and behaviour. PVY is spread by both seed and aphids.
17. īąTransmission
a.) Mild mosaic/Interveinal mosaic
īSpreads mechanically through rubbing of leaves, contact of infected plants
(Sap inoculation), seed, cutting knives, farm implements.
ī Root clubbing of healthy and diseased plants in field
b) Severe mosaic â Potato virus Y (PV Y)
ī Infected tubers (Sap inoculation)
ī Spread by aphids, Myzus persicaeand Aphis gossypii
īąManagement:
īDisease free seed tubers for planting.
īResistant varieties (like chippewa & Irish cobs).
īUse of disease free certified seed.
īRouging of diseased plants and burying them deep in soil.
īInsect control in case of Mild and Rugose mosaic.(Phorate 10G ,10Kg/ha)
īAvoid working of labour and animals from diseased to health crop in case
of latent mosaic virus.
īEarly harvesting of the crop.