the chromosome number count and flow cytometry analysis are standards, but you can try to measure stomata guard cells size and chloroplast number. http://link.springer.com/article/10.1007/BF00051583   

Can you use Cytogenetic methodology to study them (such as counting chromosome numbers)? Or you can only resort to Morphological and Cytological methods only? 

One can distinguish diploids with diploids based on growth rate (mostly diploids are slow in growth), increase in cell size, plant size and other plant parts. You can also verify by increase in stomata size, decrease in no, plastid no. in stomata and by counting chromosome no.. The attached links may be helpful for the methodology. Present day flow cytometry is the most reliable and best option.

Dear,

As far as I know, in any crops with increase in the level of ploidy from 2n basis (3n,4n,..), we would normally have bigger leaves, stems or even roots as compared to its 2n peer.

Source: Koutoulis A, Roy AT, Price A, Sheriff L, Legget G. DNA ploidy level of colchicines – treated hops (Humulus lupulus L.). Scientica Horticulture 2005; 105: 263 - 8. 

Generally, tetraploids are more viguorous than diploids in most of the morphological aspects. You may also have increased biomass in tetraploids. Other common methods have already been indicated by several members.

Thank you all for your contributions