Has 100% RH worked for you before? Generally I use a dew chamber to get free water on the plant for rust inoculation. If I don't have a dew chamber, I spray the plant with water and then inoculate, tying a plastic bag around the plant overnight to keep the water from evaporating. A mist chamber would also work. Aside from that, rusts can have particular requirements; sometimes we hydrate rust spores overnight before using them for inoculations. If you need details on that, I could ask one of my colleagues who works with stem rust and get the exact protocol from her.

I recommend Nina's answer

Best Regards

Nina Shishkoff thank you so much for valuable infos

we have mist chamber I would be greatful if you send me the exact protocol

Thank you

The attached paper has the protocol my colleagues routinely use for soybean rust. If the spores aren't fresh, they heat-shock them at 40 C for 5 min, then hydrate them by floating a mass of spores in a weigh boat on the surface of water in a Petri dish.

They kindly supplied their protocol

thank you very much Nina I will be printing it and share with collegues it in the lab we will use it and make the most of that gift

Thank you again

Hi Before you start your experiment you should check the spore germination on water Agare plate, it should show more than 75% to get a good infection.

If your friend is confident in the viability of the spores, then your colleagues can try to keep inoculated material in a damp chamber for more than 12 hours: 24 or even 48. And the temperature regime is very important. In case of problems with infection, it is impossible to go beyond the level of the optimal temperature: no more than "plus / minus" 2 degrees C! In addition, they must be clearly sure that the infected material is susceptible. By the way, the incubation period can be very long. And further. For rust on sunflower, I can say that artificial infection by using teliospores is difficult, in contrast to infection with uredospores . Good luck to your friend !