Citrumelo
Citrumelo or Citromelo is also called Swingle citrumelo trifoliate hybrid, because it is a cold hardy citrus hybrid between a 'Duncan' grapefruit and a trifoliate orange, developed by Walter Tennyson Swingle.
Citrumelo is widely employed as a citrus rootstock, being resistant to the severe citrus tristeza virus and to the Phytophthora foot rot as well as to blight, cold, and citrus nematode.
It produces yellow fruit which taste and smell like an ordinary grapefruit. The trees are very hardy and can survive temperatures as low as 30s.Taxonomy
Trifoliate orange, according to Swingle, belongs to a citrus related genera, called Poncirus, while grapefruit equivocally belongs to the genus citrus, hence the botanical name X citroncirus is a hybrid genus, derived from citrus and poncirus.
