PROBLEMS IN WALNUT BREEDING 
The Industry in California Being Transformed Through Propagation of Grafted 
Trees—Walnut Blight and the Variability of the Present 
Groves—the Ideal Commercial Nut' 
L. D. BATCHELOR 
University of California Citrus Experiment Station, Riverside, Cal. 
HE walnut industry of California 
is just entering a _ transition 
period, from the planting of seed- 
ling groves to the establishment 
of plantings composed of grafted trees. 
Just as other seedling fruit trees, 
such as the orange, apple, peach, 
almond, etc., have been eliminated, so, 
too, the seedling walnut groves of 
California seem doomed to be replaced: 
by clonal varieties. In many ways 
this industry is as much in its infancy 
as the apple industry of New York was 
sixty-five years ago, when varieties first 
began to be propagated in a commercial 
way by grafting and budding. This 
readjustment in the walnut industry is 
well started, and although it is likely 
to be gradual in its evolution, and wisely 
so, the change seems nevertheless cer- 
tain. There are but a very few seedling 
trees for sale at the present time by the 
progressive nurseries, and in fact only 
a very few such trees have been set out 
in groves during the past four or five 
years. This demand for a grafted tree 
has been brought about largely by the 
wide range of variation in walnut 
seedlings, as regards their productivity, 
commercial value, season of harvest and 
ability to resist the walnut blight. 
With this very recent propagation of 
the walnut by grafting, which has 
extended over only ten or twelve years, 
it is reasonable to expect that the 
majority of the varieties thus propagated 
so early: in the development of this 
industry are only partly suited to the 
needs of the walnut grower. The 
nuts from many of these grafted 
varieties fall considerably short of the 
commercial standard for high-grade 
walnuts. Some of the heaviest-bearing 
sorts, such as the Chase, Prolific and 
El Monte, produce nuts which cannot 
be sold in the very best grade of the 
commercial product. On the other 
hand the Placentia, which produces the 
most nearly ideal commercial nut, is not 
a heavy-producing variety, especially in 
the northern walnut sections, and is 
quite as susceptible to walnut blight as 
the average seedling tree. Again, the 
Eureka variety, which seems success- 
fully to avoid the walnut blight during 
many seasons by its lateness in coming 
into bloom, is a very moderate yielding 
sort in the southern sections. The 
above examples are only a few of many 
which might be cited to show the 
shortcomings of most of the varieties of 
walnuts now being propagated. 
MANY VARIETIES NEEDED 
The wide range of climatic and soil 
conditions makes the eventual propaga- 
tion of quite a large number of varieties 
inevitable. While the coast regions are 
bathed in fog nearly every morning 
during the growing season, the inland 
valleys experience an extremely dry 
climate with high maximum tempera- 
tures. Walnuts are being grown at the 
present time on soil types varying from 
the extremes of sand to heavy clay 
loams. Many of the future varieties 
must be especially adapted to some one 
of these particular environments if they 
are to withstand the test of time. 
Many of the present seedling groves 
are of uncertain origin and represent 
greatly varying values. No doubt some 
1 Read before the twelfth annual meeting of the American Genetic Association, at Berkeley, 
Cal., August 5. 1915. 
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