Nordmann Seedless - why?

[martweb]

Nordmann Seedless is derived from Nagami. Why is it seedless? Can't it produce seeds in generell or is it pollen sterile?

[brian]

  I'm not sure why the genetic cause is, but it is always seedless even when cross-pollinated.  I have three Nordmann trees plus fifty other flowering citrus including a regular Nagami and I have eaten thousands of Nordmann fruit over the years and never found a single seed.

EDIT- it was a seedling, not a limb mutation

    
from UCR site:

Parentage/origins(DK): George Otto Nordmann discovered the variety now known as ‘Nordmann Seedless’ on a Nagami seedling tree planted in 1965 in DeLand, about 20 miles southwest of Daytona Beach. This was one of many citrus seedlings which he grew in order to obtain virus-free budwood. “He grew seedlings of Nagami, and when they fruited he saw that one of the trees had fruit that was seedless,” said Bill Nordmann in 2003.

[martweb]

Strangely I found one fruit with a single seed today.

[Melenduwir]

There are other varieties of citrus that are considered to be truly seedless, as opposed to 'commercially seedless' strains that can have between one and six seeds in each fruit.  It seems to be due to a variety of mutations that render the plant truly sterile; at least one such variety is triploid.