Coldhardiness signs on Citrus plants ?

[tedburn]

Besides Poncirus, Citranges and Citrumelos which are very frost hardy, there are a lot of citrusvarieties which are frosthardy down to -10 or -12 ° C, but with good edible fruits. The question is now, if wer seed fruits of this varieties (especially if free pollinated) are there signs on the seedlings which already indicate a probpably high frosthardiness ?
For example I seeded Nippon Orangequat seeds and one seedling has extremely leathery leaves, see picture below.
But is there a correlation between leave thickness and frost hardiness ?

[martweb]

Could that be a tetraploid?

[tedburn]

Yes, I assume that. Will plant her in ground next spring and a smal twig graft on Poncirus or FD in ground.

[molbob]

Whats the benefit and downside of a Tetraploid? I have a seedling of polyembryonic navelina i believe that survived this winter of -6°C. How do you identify Tetraploids?