Perhaps you have seen this before. A method that was used to save the Parent Washington Navel. This is in fact a foundation for the development of Multiple Rootstock technique as different types of rootstocks were actually used.

In this case, bridge grating was used to save the tree against phythophtora damage. The three types of rootstocks used means that it has indeed multiple rootstocks. And I believe it can overcome any problem related to benching. This is hard to refute real life example of prolonging the life of citrus trees, for the nay-sayers who still believe that there are no benefits to such methods.

See how neatly the progression of the long term repair process.

http://www.saalfelds.freeserve.co.uk/riverside/pwn.htm

One of the follow-up question is that, can we improve the flavor of an existing tree down the years by inarching supposedly better rootstocks to it?

for example, if the rough lemon rootstocks did not produce good flavored fruits unto your mandarins in your specific area, can you plant Flying Dragons and Cleopatra mandarins around it and then inarch them. This should help improve chances of long term survival of the tree, but will the flavor improve?

The fact is that one type of rootstocks used to save the Parent Washington Navel tree are rough lemon (three of these were used) doesn't seem to lower the quality of the fruits. But there is it inarched together in of the presence of two other types (three of each) that imparts good flavor.

Myself and Citrus Josephine visited the Parent Washington Navel tree this spring. The tree is located downtown Riverside, California at the very end of the intersection where 4 streets come together. The only portion of ground that is not under asphalt or concrete is the small triangle around the tree. Cars whizz by just feet of the tree on three sides.

Millet,

I hope to visit the tree myself. Been down at Riverside at least twice a year and never got the chance to pay respect to the living venerable tree. Thanks for the reminder.