See:

Maluszynska J. (2003) Cytogenetic tests for ploidy level analyses — chromosome counting. In: Maluszynski M., Kasha K.J., Forster B.P., Szarejko I. (eds) Doubled Haploid Production in Crop Plants. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-1293-4_51

Thank you Clesnan_Mendes-Rodrigues for your reply

You can use the same technique for chromosome counting in root tips, but you must increase time for pre-treatment in about 8 hours (or overnight) instead of 3 hours in 8-hydroxichinoline saturated solution at room temperature, and the staining time if necessary until 2 o 3 days. Previously you must clean out perule of shoot tips or apical buds.

Thanks a lot Graziana Fiorini for your answer