Ponderosa lemon
The ponderosa lemon originated in roughly 1887, and is believed to come from a chance seedling grown in Hagerstown, Maryland. It was later named and introduced to the nursery trade in 1900. Though often referred to as a cross between the lemon and citron, a recent genomic analysis showed it to solely contain pomelo ("Citrus maxima") and citron ("Citrus medica") DNA, perhaps being an F2 hybrid. Thus they cannot derive from true lemons, which have a mandarin orange component.
Moroccan citron
As to the Diamante citron (Yanova) and the Greek citron (Corfu), he argued based on the booklet from the Salant partners, that since some of them are proven to be grafted, no certification may be granted to the rest, since it is impossible to determine if the non-grafted citrons are not descendants of the grafted ones.
As to the Moroccan and Yemenite citrons he argued, that although there were no grafted trees ever discovered among those kinds, they should be unfit, in light of the differentiation from the Ashkenazi types. The Moroccan citron is allegedly noted for its seedlessness, and the Yemenite for its pulplessness, both are too much different in morphology from the traditional Yanova and Israeli esrogs.