Twenty Years of Black Walnut Genetic Improvement at Purdue University

In 1967 a black walnut tree improvement program was initiated by Purdue University for the state of Indiana. Techniques of superior tree selection, grafting, controlled pollination, close-spaced progeny testing, and early second-generation selection were developed. The success of this program has been demonstrated by the establishment of 40 acres of clonal and seedling black walnut seed orchards and the production of 30,000 improved seedlings in 1986 and 1987. Nine patented clones, the first patents granted for timber purposes, were released to private industry for production and sale. Based on selections presently in the state seed orchards, improvement was 2, 5, 13, and 12% for height, diameter, volume, and stem form, respectively, over nursery-run checks. North. J. Appl. For. 6:68-71, June 1989.