Green Horizons

Mark Coggeshall, tree improvement specialist, shoots pollen into a pollination bag on black walnut. During controlled pollinations, specific trees are bred based on a suite of desirable traits.

Applied black walnut breeding program
An applied breeding program to develop new black walnut nut varieties for use in agroforestry-based systems was initiated in 1996 at the University of Missouri Center for Agroforestry. Since then, a total of 105 different black walnut nut cultivars have been acquired and placed in a series of grafted orchard collections at the University of Missouri Horticulture and Agroforestry Research Center (HARC) in New Franklin, Mo. Each cultivar is represented by at least two grafted trees in these clonal repositories.

Beginning in 2000, a series of careful observations were initiated on an annual basis for all of the repository trees. This information allows us to learn more about how a species can vary for a number of adaptive and commercially important characteristics. Among these adaptive traits are budbreak date, flowering habit, nut harvest date and season length. Some of the important commercial traits of interest include: early and annual nut productivity, disease resistance, nut size and kernel percent.

Genetic "fingerprinting" of cultivars
In addition to these traditional descriptor values, we have also initiated an effort to further characterize these trees on the basis of their unique "genetic fingerprint." This project has proven quite valuable, as it can help define the trees within our collection that are closely related, or may be mislabeled. These results are helping to accurately identify all the trees in the Center’s collection, which is critical to our overall goal of developing new nut cultivars for Missouri.

Cross-pollinating for desired traits
By using these high-tech tools and studying how trees vary for commercially important traits, we can define the "best" trees in our collection to serve as potential parents in a breeding program. Specific trees are crossed based on their suite of desirable traits, using traditional control-pollination methods. These efforts have resulted in 160 control-pollinated seedling trees, which are established in a new planting site at HARC. As these trees mature, we will examine how they grow by using the same descriptive categories we employed for their parents. Those trees that outperform their parents will potentially become new cultivars.

Mark Coggeshall, far right, leads a group through the HARC black walnut research site. The trees are grown on a trellis system to stimulate the production of flowers on easily accessible branches. These flowers can then be hand pollinated to produce nuts. The nuts are sown in containers, and the resulting seedlings will be evaluated for a series of years to determine if they out-perform their parents in terms of nut quality and productivity.

Cultivation for an orchard setting
In addition to evaluating both the parent trees and their seedling offspring in the breeding program, we are also very interested in developing a better understanding of how to cultivate this species in an orchard setting. For example, pruning schedules, fertilization and pest control measures, etc., can have a major impact on orchard productivity and profitability, and we are beginning to address these important questions. Also, since black walnut cultivars must be propagated via grafting, the selection of specific rootstocks for use in establishing new orchards may be very important. In fact, results from a young rootstock study indicate that both the planting site and rootstock source can have a major influence on early seed production, at least at age 5. It will be interesting to see if these early results will predict future orchard productivity.

Through these efforts, we have learned that black walnut is a species that has great potential for use in future orchard plantings. It is highly diverse for all of the adaptive and commercially important traits we have examined so far. This significant genetic diversity will allow us to make major strides in developing new cultivated varieties for Missouri in the future.