DR. CRANE: The reason why I asked, as I reported in previous meetings--they are having very serious difficulty in Oregon and in parts of Washington with graft union trouble which is known as "black line." All or practically all of the walnuts in both Oregon and California and also what few are grown in Washington have been propagated on the Northern California black walnut, _Juglans Hindsii_. No graft union trouble evidence shows up before the tree has been grafted about 8 years, and then such cases are very rare. But after the trees or the grafts attain an age of 15 years or more, graft union failures are numerous. For three years now we have been making surveys in the State of Oregon, and we have surveyed tree by tree, year after year, the same orchards, the same trees, and our observations now go into the thousands, and we find that this black line is a terrifically serious thing. In some orchards 22 per cent of the trees will develop black line in one year's time. So, you see, at that rate it would only take you five or six years with a good bearing orchard until you wouldn't have any.
DR. MACDANIEL: Is that always with the Franquettes?
DR. CRANE: That is not only true with Franquettes but also with other varieties in California, even in Contra Costa County.
MR. STOKE: Where those trees are so grafted, does it tend to overgrow, or just the opposite?
DR. CRANE: No, it appears much like our _Crenata-mollissima_ chestnut graft union failure.
MR. STOKE: Is there a tendency for the top to be more vigorous, to have more growth, or vice versa or is growth uniform?
DR. CRANE: It may be uniform. Depends somewhat on the varieties and the seedlings. There may be some overgrowth or some outgrowth, but there is only one test for it, and that is at the graft union. With an axe or knife and you cut out a strip of bark across the union. It may look absolutely perfect, but if there is a black line developed there that is just like a lead pencil line between the stock and the scion, the tree is on the way out. It's just a matter of time. Ultimately the bark between the stock and scion will split, and you get infolding, just like on the chestnut.
One of the reasons that they have propagated their trees on Northern California black walnut was that they had the idea that the Northern California produced a stronger, more vigorous seedling and that they grew much faster than seedlings of the Persian walnut. And, furthermore, somebody at some time circulated the idea that Northern California walnuts were immune to infection by the mushroom root rot fungus. We have surveyed thousands of trees of Persian on Persian roots, and we have never found a single case of black line developing or graft union failure as long as it's a Persian on Persian, and we find the same percentage of infection from mushroom root rot fungus on Persian as on Northern California black.