Alex Ignatov Do we have virus fast testing kit (for these viruses) for potatoes?

Yuan-Yeu Yau Yes, we have commercial routine testing for these potato viruses and viroid by real-time PCR and ELISA. I have met several PVY modifications but none of them gave such damage. Althogh, PVY lesions can be unpredictable at unusual year weather, like 2020. This spring was generally too cold for potyviruses - only a few days with temperature above +16oC. .

Hi,

Can you exclude bacteria or even some insects/caterpillars. Also is your soil/growth medium balanced for nutrients (Fe, N and P shortage can all result in paler leaf). How does the back of the leaf look, anything specific on it?

Svetlana Boycheva Woltering Svetlana, it was too cold for bacteria but I will check, it was too cold for insects as well. Only a few plants were affected - all nutrients are in reccomended dozes. Back side has no visual difference from healthy leaves, exept one leaf with small blackenning on middlerib. It looks like some systemic infection or physiological disorder.

Hmm, what about fungal?

Svetlana Boycheva Woltering I am waiting for isolation results. So far, younger leaves comparing to normal leaf.

Some colleagues said that it was caused by night frost damage.

The blackening yes. But this curling looks like something caused by disordered hormones as a result of some pathogen. What about insects?

Svetlana Boycheva Woltering The main rib blackenning was developing during incubaction in wet chanber for 24 -48 h. I am just waiting to presence/absence of any microorganisms on Petri plates.

If they are obligate pathogens, no culturing will show anything.

You can always isolate DNA from the symptomatic tissue, and amplify ITS, cox (for fungi) or 16S for bacteria using universal primers.

If only potato PCR product present - either virus or physiological effect.

Marcin Nowicki Thank you, Marcin. This year is unusual, it can be everything.

Nice Contribution Marcin Nowicki

Everybady, thank you for your suggestions. So far, yellow slow-growing gram+ bacteria were isolated from main rib veins of affected leaves and were not - from normal leaves.

Hello,

I agree with dr. Marcin Nowicki , let us know what PCR results are going to be.

I personally think is a combination of biotic and abiotic stress and indeed the crackling might look like a virus but without proper diagnostic results it appear difficult to assess the right cause.

I would suggest to test for 16S since in the first picture shown there is some yellowing on the border as in many bacterial damages (first picture).

Best regards,

Francesco Desiderio

I agree with @Francesco's answer!

I agree with Marcin Nowicki however I have had success culturing obligate pathogens such as grape powdery mildew and grape downy mildew on sterilized leaves placed on water agar. If there are symptoms on the potato, I don't know how it would work , but a similar technique may be worth exploring (slices or whole vegetable). I have also made my own "PDA" by making a slurry of potato, boiling it to release the nutrients then adding agar and autoclaving. I think this may be a possible route to culturing the pathogen as well. However, obligate pathogens are never fun to work with. Hope this helps or sparks new ideas. Good luck!

Thanks to Everybody for comments and ideas!

I can assume that it was late frost reaction of plants, all the symptoms had no further development, new leaves look healthy. The isolated bacteria belonged to non-pathogenic genus.

these type symptom may be due to frosting.

I think these symptom is due to frost reaction.