Sclerotinia Stem rot of sunflower
Etiology:
Pathogen: Sclerotinia sclerotiorum
• Hyaline multicellular hyphae.
• Sclerotium germination occurs in myceliogenic -hyphae and carpogenic –apothecia.
• Myceliogenic germination of sclerotia- root rot, stem rot and wilting.
• The apothecium is a flat or cup-shaped structure that produces sexual spores of
S.sclerotiorum.
• Asexual – hyphae and sclerotia Sexual–ascospore.
Disease Cycle:
• Primary source: Black, hard sclerotial bodies perpetuating in the soil and plant debris.
• Secondary spread: Through conidia along with irrigation or rain water.
Sclerotinia Stem rot of sunflower
Symptoms:
• The disease begins on stems near the soil level.
• White cottony fungal growth on infected stem near soil level
observed.
• The roots get rotten with bark shredding symptoms.
• Black sclerotial bodies are formed on or inside the stem.
• The plant shows complete wilting and drying.
Favorable conditions
• Alternate periods of high soil moisture and water stress
conditions predispose the disease.
Sclerotinia Stem rot of sunflower
Management:
• Crop rotation of 3-4 years helps to reduce disease.
• Elimination of infected plant residue.
• Deep ploughing of soil.
• Moisture stress and water logging conditions should be avoided in the field.
• Seed dressing with thiram + carboxin (2:1) at 3-6 g/kg of seed is found to be effective control of the seedling
phase of the plant.
• Spray Validamycin@0.2%.
Alternaria blight-Sunflower
• In areas of tropical and subtropical climates.
• It is the most destructive disease and is widely distributed wherever
sunflower is grown.
• This disease has been reported to reduce the seed yield by 27 to
80%
• The disease also affects the quality of seeds which adversely affects seed
germination and vigour of seedlings.
Etiology:
Pathogen: Alternaria helianthi
• The fungus produces cylindrical conidiophores, which are pale grey-
yellow coloured, straight or curved, geniculate, simple or branched,
septate and bear single conidium.
• Conidia are cylindrical to long ellipsoid, straight or slightly curved, pale
grey-yellow to pale brown, 1 to 11 septate with transverse and
occasionally longitudnal septa measuring about 40-110×13-28µ.
• Conidia are not formed in chains.
Alternaria blight-Sunflower
Symptoms:
• The fungus produces brown spots on the leaves, stem,
sepals and petals.
• The lesions on the leaves are dark brown with pale margin
surrounded by a yellow halo.
• The spots enlarge in size with concentric rings and become
irregular in shape.
• Several spots coalesce to form bigger irregular lesions
leading to drying and defoliation.
Alternaria blight-Sunflower
Favorable condition:
• Rainy weather.
• Cool winter climate.
• Late sown crop.
Disease cycle:
• The pathogen survives in the infected host tissues and weed hosts.
• The fungus is also seed borne.
• Secondary spread mainly through wind blown conidia.
Management:
• Grow tolerant variety like KBSH-1,APSH-1.
• Remove and destroy infected plant debris.
• Rogue out weeds at periodical intervals.
• Treat the seeds with thiram or carbendazim @ 2 g/kg.
