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.
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.
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.
Average Average Average straight- anthrac- Average diameter ness nose Late Nut Name Origin Age height @4 1/2 ft. rating* resistance* leafing+ crop --------------------------------------------------------------------------------------------- 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 - ----------------------------------------------------------------------------------------------- * 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 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 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.
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 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.
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.
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.
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.