THE IDENTIFICATION AND CHARACTERIZATION OF A GENETIC-MARKER LINKED TOHYPERSENSITIVITY TO THE CHERRY LEAFROLL VIRUS IN WALNUT

Walnut blackline disease, caused by the walnut strain of the cherry le afroll virus, causes fatal necrosis of the graft union between suscept ible, infected scions of Persian walnut (Juglans regia L.) and hyperse nsitive, resistant rootstocks. A backcross breeding program to transfe r hypersensitivity to cherry leafroll virus from the Norther Californi a black walnut (Juglans hindsii (Jeps.)), into Persian walnut was begu n in 1987. Hypersensitivity to the virus is inherited as a single, dom inant gene. The current procedures for identifying hypersensitive back cross progeny are slow and labor intensive. Bulks of DNA from backcros ses that were either hypersensitive or susceptible to cherry leafroll virus were compared using randomly amplified polymorphic DNA. One rand om decamer, sequence 5'-CTCCTGCCAA-3' (OP-K15), produces a polymorphic fragment of about 720 bp that has about 7% recombination with hyperse nsitivity to cherry leafroll virus in our backcross populations. The p olymorphic fragment was cloned and converted into a restriction fragme nt length polymorphism to demonstrate that it is a distinct, low-copy sequence.