Sunflower young plants show retarded growth, surface necrosis and cracks of undersoil stem part, necrosis of leaf petioles, young top leaves are dead. There is no evidence of bacterial or fungal infection on necrotic parts. Damaged plants were found in large spots (10 x 5 m) inside different fields. Soybean and wheat were in crop rotation previously. No any fungicide treatment. Is it virus infection (tobacco steak virus, etc.) or something else?
Dear Alex, Have you surface disinfested the areas of advancing necrosis and plated them on a general media like potato dextrose agar PDA? If not I would suggest that and some moist chamber study. To me the symptoms are similar to a condition called wirestem. That symptomatology of shrunken stem and root basal plant is often the result of rhizoctonia solani. The rhizoctonia would not sporulate but does produce a very characteristic mycelium which is dark wide with a constricted branching and can have characters like clamp connections from its basidiomycete affinity and doliopore septa. You may want to check for it as symptoms are not conclusive. If you isolate use the well washed plant parts and cut pieces at the margin with are surface sterilized with 10% bleach for 4 minutes rinsed in sterile distilled water and dried off aseptically than plated of the PDA
@Paul, thank you for rapid response - I placed plant fragments with necrosis to different nutrient agars (PDA, YDC, NA, LB, King's B), but, so far I have found only slow-growing yellow-pigmented bacteria. I would say "Clavibacter- or Xanthomonas - looking", but they have not been tested yet for any properties. I am afraid that disease development was too rapid for R. solani. I was thinking of virus infection because plant tissues were clean of saprophytic microorganisms, and it happens after necrotic damage by some viruses.
Alex
Curtobacterium flaccumfaciens +some secondary pathogenic pseudomonas spp.
Hi Alex
You can do a separation for microorganism then inoculate a healthy plant and checking the symptom
May be this way can help you
Virus, I don't think so, because the affected area is isolated and leafs not have any symptoms of viruses. Do you found some insect associated with them?
Do again the isolation of possible pathogen from the margin of diseased and healthy tissue, using less time on the ethanol and NaOCl.
Leonardo, several isolations gave the same result: C. flacumfaciens and Pseudomonas marginalis. The pathogens gave similar symptoms after seedlings inoculation. Seeds were infected.
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