PL PATH-515: Diseases of Field

and Medicinal Crops

Department of Plant Pathology, College of

Agriculture, CSUA&T, Kanpur, (U.P.)
 Mustard diseases

Prepared by: Dr. Manoj Kumar Chitara

Alternaria blight
 Symptoms
• The disease attacks the lower leaves as small, circular brown necrotic spots
that slowly increase in size,
• Many concentric spots coalesce to cover large patches showing blightening
and defoliation in severe cases.
• Circular to linear, dark brown lesions also develop on stems and pods,
which are elongated at a later stage,
• Infected pods produce small, discoloured and shrivelled seeds.
 Etiology
• CaO: Alternaria brassicae and A. raphan
• Classification
K. - Fungi
D. - Ascomycota
C. - Dothideomycetes
O. – Pleosporales
F. - Pleosporaceae
G. – Alternaria
S. – A. brassicae
 Survival and spread
• The disease is externally and internally seed-borne,
• The pathogen survives through spores (conidia) or mycelium in
diseased plant debris or weeds.

Favorable conditions
• Moist (more than 70% RH) coupled with warm weather (12-25°C) and
intermittent rains favors disease development.
Disease
cycle
 Management
• Follow crop rotation,
• Clean seed to remove shrunken seed that may be infected with black
spot and have low viability,
• Use seeds with high germination (over 90%),
• Application of T. viridae + FYM + Neem oil (3%),
• Foliar application of azoxystrobin + hexaconazole 0.1%
White rust
 Symptoms
• White to creamy yellow pustules develop on the lower leaf surface,
• The pustules, later coalesce to form patches on the lower leaf surface,
• Tan-yellow spots develop on the upper leaf surface opposite the pustules.
• Pustules may also form on the pods,
• Infected flowers develop a "staghead" in which the flowers are sterile,
malformed and green, and various flower parts may be thick and club-
shaped and greatly enlarged,
• Yield losses are about 1% for each 1% of staghead observed in a field.
 Etiology
• CaO: Albugo candida
• Classification
K. - Fungi
P. - Oomycota
O. – Albuginales
F. - Albuginaceae
G. – Albugo
S. – A. candida
 Survival and spread
• The pathogen survives through oospores in affected host tissues and
soil,
• Secondary infection is carried out by sporangia and zoospores which
produce new infection.

Favorable conditions
• Moist (more than 70% relative humidity) coupled with warm weather
(12-25°C) and intermittent rains favours disease development.
Disease cycle
 Management
• Grow resistant cultivars such as Argentine,
• Follow three-year crop rotation,
• Control volunteer canola and susceptible mustard-type weeds in the
rotation,
• Regular spray of Mancozeb 0.25%,
• Seed treatment with T. viride+spraying of T. viride,
• Seed treatment with P. fluorescens+ spraying of P. fluorescens
Downy mildew
 Symptoms
• Leaf spots initially are angular, translucent, and light green, later
developing into greyish-white irregular necrotic (dead) patches,
• The stems of flower clusters become swollen,
• Frequently associated with white rust,
• May develop late in the season on turnip-type (Polish) canola
varieties.
 Etiology
• CaO: Hyaloperonospora parasitica
(formerly Peronospora parasitica)
• Classification
Domain - Eukaryota
Clade - Diaphoretickes
Clade - SAR
Clade – Stramenopiles
Phylum - Oomycota
Family – Peronosporaceae
Genus – Hyaloperonospora
Species – H. parasitica
 Survival and spread
• The pathogen survives as oospores on the affected plant tissues in soil
and weed hosts.

Favorable conditions
• Temperature: 10-20°C and
• RH: >90% RH
Disease cycle
 Management
• Destroy crop residues,
• Follow crop rotation,
• Grow resistant cultivars,
• Spray of Azoxystrobin (quadris), Copper fungicide (Basicop, )
Sclerotinia Stem rot
 Symptoms
• The stems develop water-soaked spots which later may be covered with a
cottony white growth,
• As the disease progresses, affected portions of the stem develop a
bleached appearance, and eventually the tissues shred,
• Girdling of the stem results in premature ripening and in lodging of plants,
• Hard black bodies, the sclerotia, are formed inside the stem and
occasionally on the stem surface,
• Basal stalk infections rarely occur,
• Yield loss of 10 to 15% have occurred and occasionally losses of 50%
 Etiology
• CaO: Sclerotinia sclerotiorum
• Classification
K. - Fungi
D. - Ascomycota
C. - Leotiomycetes
O. – Helotiales
F. - Sclerotiniaceae
G. – Sclerotinia
S. – S. sclerotiorum
 Survival and spread
• The pathogen survives as mycelium in dead or live plants and as
sclerotia in infected plant parts
or
on the soil surface or with seed as a contaminant.

Favorable conditions
• High humidity (90-95%) and average temperature (18-25°C) along
with wind current favours the disease development.
Disease cycle
 Management
• Follow crop rotation - at least a five-year rotation for severely infested
fields,
• Grow resistant cultivars,
• Follow clean cultivation,
• Avoid dense planting,
• Avoid planting next to a field that had severe Sclerotinia in the past
four or five years,
• Control broad-leaved weeds,
• Seed treatment with Carbendazim 2 g/kg seed and 0.2% foliar spray,
• Seed treatment with Trichoderma spp., Pseudomonas fluorescens, and
foliar spray was effective.