FNR-115
WOODLAND MANAGEMENT
Cooperative Extension Service
Purdue University
West Lafayette, IN 47907
Characteristics of Purdue University's Patented
Black Walnut Trees
Walter F. Beineke, Associate Professor of Forest Genetics
Introduction
The harvest of high quality black walnut (Juglans nigra L.) trees has been
accelerating for many years. The best trees are cut to be processed into
veneer and lumber, leaving the inferior trees to produce succeeding generations.
To reverse this trend, research to genetically improve black walnut was
initiated at Purdue University in 1968. The research objectives were: (1)
to locate and preserve, through grafting, the best remaining trees; (2)
to develop methods to discover how traits were inherited and to what degree;
and (3) to develop seed orchards for the production of genetically improved
seed.
Black Walnut Improvement Program
Original selections were made from wild trees found in forests, parks, yards,
and plantations in the Midwest. A rigorous screening system was applied,
based on form and growth observations, to determine the trees to be tested
for superiority.
Grafting wood was collected from the superior selections, and grafts were
planted in the research clone bank at Martell Forest 10 miles west of the
Purdue campus. Since all the grafts are growing in essentially the same
environment, differences in growth rate, form, and disease resistance are
genetic. Grafting captures and preserves the genetic identity of the superior
selection and transfers its genetic advantage intact to the next cycle of
grafts.
We have learned that black walnut has tremendous genetic variability in
growth rate, stem form, date of leafing, disease resistance, and nut production.
These traits are inherited to a degree that allows for rapid genetic improvement.
Selections grafted in the clone bank that consistently produced seedlings
with improved characteristics, or were themselves superior, were grafted
into production seed orchards by the Division of Forestry, Indiana Department
of Natural Resources. These seed orchards will ultimately produce seed for
seedlings to be grown and sold to landowners. However, most of the seed
orchards are 8 to 10 years away from significant seed production. Black
walnut has proved to be very erratic in flower and seed production. Several
selections, which when grafted displayed exceptional growth rate and tree
form, were among the poorest producers of flowers and seed. Landowners,
reluctant to wait for improved seedlings from the state seed orchards, requested
access to grafted trees. Grafted trees theoretically are exact genetic copies
of the original selection and do not suffer from the inherent variability
of seedlings produced through the sexual process where the pollen parent
is unknown and often of inferior origin.
Patented Black Walnut Cultivars
Plant patents provide protection for vegetatively propagated plants against
indiscriminate propagation and sale so that the organization that made the
discovery can recoup its investment in research. Therefore, patent applications
were filed on the better performing cultivars and offered for licensing.
In 1977, a group of Indiana businessmen formed a company and negotiated
a license agreement with the Purdue Research Foundation to produce the grafted
cultivars. This company has exclusive propagation rights to the walnut clones.
Presently, grafted trees are being marketed.
Even though the clone banks were not designed to thoroughly test the selections,
and the number of grafts of each clone was limited, statistical analyses
of the clone bank grafts have shown that differences in most traits are
real and are significant.
Measurements and ratings shown in Table 1 are based on grafted trees grown
at Purdue University's Martell Forest 10 miles west of West Lafayette, Indiana.
The planting is located in the Indian Creek bottom near the Wabash River
at an elevation of 540 feet. The soil is a Genesee sandy loam and is one
of the better soils for walnut growth, although it tends to be droughty
due to extensive sand and gravel deposits within 3 to 5 feet of the surface.
A standard seedling plantation is planted on the same soil type next to
the clone banks at Martell Forest. Seedlings were planted as 1-0 stock from
the Indiana Division of Forestry Nursery. The standard planting has had
excellent care and management over the years. Annual measurements have been
taken on the standard plantation. Therefore, the superior selections and
the standard plantation can be compared at the same ages (Table 1).
It can be assumed that the patented trees will do well on good sites in
the central region of the natural range of black walnut including all or
portions of the states of Indiana, Michigan, Illinois, Ohio, Missouri, and
Kentucky. They will possibly outgrow local trees in other areas of the country.
However, this cannot be stated with certainty without testing. Growth and
form of grafted trees will vary even though they are genetically identical,
because of factors such as soils, site, climate, weed control, fertilization,
irrigation, pruning, and rootstock.
Table 1. Characteristics of the patented black walnut clones at Martell
Forest, West Lafayette, Indiana.
Average Average
Average straight- anthrac-
Average diameter ness nose Late Nut
Name Origin Age height @4 1/2 ft. rating* resistance* leafing+ crop
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ft. in. days no./
tree/
yr.
Purdue 1 Montgomery Co. 20 56 11.4 1.0 2.9 3 earlier 800
Lawrence 2 Lawrence Co. 20 54 10.0 1.0 1.8 4 earlier 750
Av. of 2 patents 20 55 10.7 1.0 2.4 3.5 earlier 775
Av. seedling 20 44 8.3 2.9 2.8 average 180
% improvement - 25 29 66 14 -
Purdue 2 Carroll Co. 18 50 9.3 3.0 2.3 7 later 5
Tippecanoe 1 Tippecanoe Co. 18 54 11.8 1.0 2.8 4 earlier 5
Lawrence 1 Lawrence Co. 18 52 10.0 2.0 1.3 average 350
Fayette 1 Fayette Co. 18 50 10.7 3.0 1.3 1 earlier 350
Fayette 2** Fayette Co. 18 46 8.4 4.5 2.0 11 later 1,000
Av. of 4 patents 18 52 10.5 2.3 1.9 1 later 180
Av. seedling 18 39 7.9 2.9 2.8 average 150
% improvement - 33 33 21 32 - -
Purdue 3 Morgan Co. 16 48 8.7 1.3 1.5 11 later 120
Knox 1 Knox Co. 16 49 7.7 3.0 1.3 6 earlier 300
Av. of 2 patents 16 49 8.2 2.2 1.4 2.5 later 210
Av. seedling 16 36 7.1 3.1 2.8 average 130
% improvement - 36 15 29 50 -
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* From 1 = excellent to 5 = very poor.
+ Late leafing avoids late frosts which damage opening buds and new growth.
** Fayette 2 not averaged since patented for nut production only.
Height and Diameter
Height is measured as the total tree height in feet. Diameter is measured
at DBH, 4 1/2 feet above ground level. Site and care affects growth rate
to a great extent. However, both height and diameter growth are under sufficient
genetic control that superiority is passed on.
Stem Form
Stem form was obtained by subjectively rating the straightness of the main
stem on a scale of 1 to 5 with 1 representing a perfectly straight stem;
2, slight crook or deviation of the central stem; 3, about average straightness;
4, several severe crooks or a single fork; and 5, a very crooked, forked,
and/or leaning central stem.
Stem straightness is perhaps more important than growth rate, since if the
bole (stem) of the tree is crooked, manufacture of high quality veneer and
lumber is not possible. Improved straightness also reduces expensive pruning
practices. Straightness is highly inherited, particularly by grafted trees.
Late Leafing
Date of leafing was measured as the number of days since the first graft
in the entire study broke bud. A graft was considered leafed-out when the
first leaf separated from the bud. The earlier in the spring a tree leafs-out,
the more susceptible it is to late spring frost damage to expanding buds
and leaves. New growth of black walnut is particularly sensitive to frost
damage. While it has been determined that date of leafing has little relationship
to growth or form, it is important if the grower is interested in nut production.
Flowers which produce the nut are borne on the new growth. If this new growth
is frost-killed, so is the nut crop.
Anthracnose Resistance
Anthracnose resistance was a subjectively rated trait using a system similar
to the stem form rating with 1 representing a tree having little or no infection;
2, slight infection, leaf lesions evident but only a few leaves fallen and
no rachis fall; 3, average leaf lesions and leaf fall, some rachis fall;
4, serious leaf and rachis fall; and 5, a tree having nearly total defoliation
on the date of observation. Anthracnose resistance data were taken in early
to mid- September. Anthracnose is a leaf disease which prematurely defoliates
black walnut. However analysis indicates that little growth reduction is
sustained from early defoliation by anthracnose. The only significant effect
of anthracnose may be on proper ripening and filling of the nut.
Nut Production
While nut production has not been a primary objective of the genetic improvement
program, several clones have significantly greater nut production at an
early age than others. A few clones have produced very few, if any, nuts.
These may be desirable under certain circumstances (yards and parks) where
messy nuts are not attractive. Also, they place their photosynthetic productivity
into wood rather than flowers and nuts.
Comparison among Patented Clones
Purdue 1 in most respects is the most outstanding of the patents. It has
rapid growth, even on some poorer sites. Straightness is excellent - the
straightest observed in any young black walnut clone, and it has a tendency
to straighten without help after wind, frost, or insect damage. Nut production
begins early - usually by age 3 or 4. Purdue 1 is an annual bearer of abundant
crops with nut set on lateral shoots, a rare occurrence in black walnut.
The only negative features include some susceptibility to anthracnose and
a slightly earlier than normal leafing date.
Purdue 2 has rapid growth, but below average straightness. It leafs out
a week later than average, a desirable trait. If a nut crop is not necessary,
Purdue 2 is a good choice.
Purdue 3 combines rapid growth and good straightness with very late leafing
and favorable anthracnose resistance characteristics. While the nut crop
is light and erratic from year to year, this is another good all-around
tree.
Knox 1 is noted for rapid growth, heavy annual nut crops, and good anthracnose
resistance, but is below average in straightness. It is susceptible to late
spring frosts since it leafs out nearly a week earlier than average.
Lawrence 1 has very rapid growth, good straightness, and excellent anthracnose
resistance. Its nut crop is abundant but tends toward alternate-year bearing.
Lawrence 2, while not so fast-growing as some of the other patents, is uniquely
suited to plantation culture. First, it is extremely straight, and second,
it is fairly short with a large diameter. This produces a tree that is very
firmly anchored and is not wind damaged. Lawrence 2 also has very good anthracnose
resistance and is an outstanding annual nut-bearer.
Tippecanoe 1 is the fastest growing of all the patented trees. It has good
straightness but is somewhat anthracnose susceptible and produces very few
nuts.
Fayette 1 is fast-growing, has average straightness, and abundant but alternate-year
nut-bearing characteristics. Its most outstanding feature is unusually strong
anthracnose resistance.
Fayette 2 was patented for its nut production. Otherwise, it has a relatively
slow growth rate and very poor straightness. It has good anthracnose resistance
and is very late to leaf out. Nuts are produced annually in great abundance
by age 3 or 4, and clusters on spur-type lateral shoots contain up to 6
nuts.
It would be highly speculative to estimate yields and economic returns from
plantations of these cultivars with the limited data available at present.
These black walnut cultivars have been released with less scientific performance
testing than is normally expected for agronomic and horticultural varieties.
But comparable testing of the species such as black walnut would require
major expenditures of funds and fifty or more years in time. Thus, we decided
to release the cultivars without specific performance data or predicted
gains. Regretfully, only time can provide the data on which to base longterm
growth and yield predictions.
RR 5/90
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana,
Purdue University and U.S. Department of Agriculture Cooperating. H.A. Wadsworth,
Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8
and June 30, 1914. It is the policy of the Cooperative Extension Service
of Purdue University that all persons shall have equal opportunity and access
to our programs and facilities.
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