What do u mean? which parameter u r going to study? 

i am  going to study with wheat genotypes resistance against yellow rust to and i want to store the uredospores. is freezer (-20 C) suitable to keep  for several months?

I am studying the urediospore germination, 15-20 degrre temp. is favourable for the same. And within half an hours spores get germinated.

Thank you Suhas...

Dear Imriz, sorry, but especially isolates of yellow rust of cereals are not easy to preserve. We have best experience with shock freezing and keeping it at minus 80 degrees Celsius. At less exposed temperatures you may get loss of Germination due to rechristalization. Some rust fungi - like Uromyces phaseoli can be kept in a regular freezer at -20 degrees Celsius for years. Brown rust of cereals can be kept for months in a refrigirator for weeks a plus 6-8 degrees Celsius. But yellow rust isolates may not be that easy. You should check it - it may be varying with different isolates. Please try and check it individually.

Thank you very much Mr Dehne....We may try three of degrees (-20, -80 , +4-6  C) for this year.

For long term storage (-80oC freezer or liquid nitrogen), uredospores can be stored in gelatin capsules, glass vials, plastic bags and aluminum foil pouches.

Thank you very much Mohammad Mohsin.

Just in addition to the recent recommendation of Muhammad Raza: - 80 degress C for long term storage can be very suitable. But the samples should be kept especially in gelatine capsules. The samples should be protected from temperature changes and the recristallisation. Depending on the rust pathogen some of them can be stored for years in a regular fridge. Believe me this is the easiest and safest way to keep the spores. But it can not be applied to all rust funigi. But you can easily find out - good luck!

Thank you very much Mr Dehne.