By Carol Constantine -

GRANDFATHER CITRUS

Did you know that horticulturists have been creating clones for centuries? You may possibly have done this procedure yourself.  UC Riverside was involved in helping develop California's citrus industry from an original of a very famous clone. Citrus varieties developed in California now grow all over the world, from Pakistan to South Africa.

This tree has many, many genetic duplicates all over the world. You may even have one growing and thriving in your own yard.  Yes, it's a navel orange, large, sweet, amazingly seedless but with a tiny extra orange growing at its blossom end. Since it has no seeds, it must be propagated from cuttings. Each new graft is an exact genetic duplicate of the parent tree.

In 1875 three small trees arrived at the U.S. Dept. of Agriculture in Washington D.C., scions of a spontaneous mutation in Brazil. The small subtropical trees were later sent to California. One was planted at the historic Mission Inn, but died later. Two were planted at the intersection of Magnolia and Arlington in Riverside, where one survives to the present day. By 1921, the original parent tree was surrounded by thousands of acres of groves containing its citrus offspring.

The lone original survivor was girdled by Phytophthora gummosis in 1918 and again in 1941. UC Riverside plant pathologists treated it by inarching, a technique of grafting on new rootstock to bypass the girdled area. The treatment worked. Unfortunately, this last survivor is now threatened by huang long bin disease, carried by the Asian citrus psyllid. UC Riverside plant pathologists recommend enclosing this historic tree in netting for protection.

Additionally, clones of every variety in UC Riverside's Citrus Variety Collection are now being kept in a nearby greenhouse, as a botanical backup.

California's citrus industry is valued at over $2 billion yearly.