Transcript MAIZE DISEASES

MAIZE DISEASES
Dr. Jamba Gyeltshen
01/04/2010
Maize Diseases
1. Turcicum leaf blight (Northern
leaf blight) (Exserohilum
turcicum syn.
Helminthosporium turcicum)
2. Grey leaf spot (Cercospora
zeae-maydis)
1. Turcicum leaf blight
Northern Corn Leaf Blight
(Exserohilum turcicum)
Syn. Helminthosporium turcicum
TLB Pathogen
Anamorph (asexual phase)
• Exserohilum turcicum (syn.
Helminthosporium turcicum)
Teliomorph (sexual phase)
• Setosphaeria turcica
1. Turcicum Leaf Blight (TLB)
Conidia are 3 - 8 septate, spindle-shaped, and have a protruding hilum.
TLB
• Major constraint to maize production
where humidity is high and temperatures
moderate (17 to 27°C).
• Cause yield losses as high as 70%
TLB Distribution
TLB Symptoms
• Cigar shaped lesions that are 3 to 15 cm long
• Lesions are elliptical and tan in color,
developing distinct dark areas as the fungus
sporulates
• Lesions typically first appear on lower leaves
and spread upwards.
• Under severe infection, lesions may coalesce,
blighting the entire leaf.
TLB Symptoms
Disease cycle
• Overwinters as mycelium and chlamydospores in
infected crop debris.
• Fungi in crop debris sporulate in response to higher
temperatures and humidity.
• Spores (conidia) are then disseminated by wind and rain
splash to freshly planted maize. Conidia can be carried
vast distances in the wind.
• They germinate in temperatures ranging from 17 to 27°C
and during periods of extended leaf wetness (6 to 18
hours), infecting host tissue.
• Secondary cycles of disease occur where conidia
produced in disease lesions are disseminated within the
crop and to other fields by rain splash and wind.
Damage
• Mechanism of damage: Yield loss is caused
predominantly through loss of photosynthetic
leaf area due to blighting. Under severe
infestation, sugars can be diverted from the
stalks for grain filling leading to crop lodging.
• When damage is important: If Turcicum leaf
blight establishes before silking and spreads to
upper leaves during grain filling, severe yield
losses can occur.
• Economic importance: Yield losses as high as
70% have been recorded but typically range
from 15 to 30%.
Disease management
• Grow resistant varieties: Yangtsepa
• Management of overwintering infected crop
residue will reduce the amount of available
inoculum at the onset of the subsequent growing
season.
• Fungicide application can effectively control
Turcicum leaf blight when applied at the right
time.
• Fungicide should be applied when lesions first
become visible on the lower leaves.
2. Grey leaf spot
Pathogen: Cercospora
zea-maydis and
Cercospora zeina
• Gray leaf spot (GLS)
is a serious foliar
disease of maize in
many temperate and
tropical highland
regions of the world.
GLS Symptoms
• GLS has characteristic rectangular, tan-colored lesions
that are contained within leaf margins, as the fungi is not
able to penetrate sclerenchyma tissue in the leaf veins.
• As lesions mature they assume a graying cast due to
sporulation of the fungi. Lesions are typically 2-4 × 1060mm in size and usually develop on the lower leaves,
gradually spreading upwards on the plant during the
season. Under severe disease pressure, entire leaves
can be blighted and lesions can develop on cob sheaths.
Symptoms of GLS caused by Cercospora zeae-maydis
and C. zeina are indistinguishable.
Symptoms as seen against light
GLS symptoms
GLS symptom severity
GLS conidia
Disease development
• In spring, conidia (spores) are produced
and disseminated to corn plants by wind
and rain splashing. They require several
days of high relative humidity to
successfully germinate and infect corn
leaves. Several weeks may be needed for
the development of mature lesions on
leaves. Conidia for secondary spread are
produced from two to four weeks after
initial leaf infection
Management
• Damage, disease cycle and management
are same as TLB
References
• http://www.apsnet.org/online/feature/grayl
eaf/gallery.htm
• http://www.ars.usda.gov/sp2UserFiles/Pla
ce/36021000/dunkle7.jpg