Freezing tolerant rootstock of citrus is

Solution (By Examveda Team)

The freezing tolerant rootstock of citrus is C. unishu.
Citrus unshiu is a semi-seedless and easy-peeling citrus species, also known as cold hardy mandarin and tangerine.
These are cold-hardy and when planted in colder locations, the fruit becomes sweeter from the colder temperatures. A mature satsuma tree can survive down to -9°C (15°F) or even -11°C (12°F) for a few hours.
It is usually seedless, but it can be grown from seed, which takes about eight years until the first fruits are produced or grafted onto other citrus rootstocks, such as trifoliate orange.