Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2007
Publication Date: 9/18/2007
Citation: Sagaram, M., Lombardini, L., Grauke, L.J. 2007. Variation in leaf anatomy of pecan cultivars from three ecogeographic locations. Journal of the American Society for Horticultural Science. 132:1-5. Interpretive Summary: Pecan trees are native to North America, and are found over a wide range of climates and soils. Over very long periods of time, trees growing in one place may have developed genetic differences that help them in that location. In breeding for trees that will do well in particular areas, we need to know which traits are related to improved performance for particular regions. We studied the leaf structure of three pecan cultivars: ‘Pawnee,’ ‘Mohawk’ and ‘Starking Hardy Giant.’ A “cultivar” is a cultivated variety of pecan, and is maintained by grafting buds from the source tree onto a rootstock. As a result, the tops of trees of the same cultivar are genetically the same. When trees of a cultivar are grown in different locations, their leaves will be genetically the same, but differences may occur due to the place where they are grown. By studying the differences between our three cultivars in three different locations (Tifton, GA, Chetopa, KS, and Stillwater, OK), we were able to see if differences in leaf structure are related more to their genetics or to the environments where the trees are grown. Our three cultivars are related to each other: ‘Pawnee’ is the offspring of a cross made by putting ‘Starking Hardy Giant’ pollen on a ‘Mohawk’ female flower. We found that the number of stomata per unit area were different between the three cultivars, with ‘Pawnee’ being between its two parents. Those patterns did not change across the locations. Cultivars also differed in epidermal cell density, but each cultivar was consistent across locations. Some plants have “hairs” on their leaves, called trichomes, that changed with environment in some plants. In our study, the number of trichomes changed across locations and between cultivars. Stomatal and epidermal cell densities are under genetic control and may be useful in studying patterns of tree performance in different regions. The other leaf traits are not as informative for genetic comparisons.
Technical Abstract: This paper assesses leaf anatomical traits (stomatal density, stomatal index, epidermal cell density, trichome abundance) of three related pecan cultivars [‘Pawnee’ (progeny), ‘Mohawk’ (maternal parent) and ‘Starking Hardy Giant’(paternal parent)] collected from three locations (Tifton, GA, Chetopa, KS, and Stillwater, OK). Acetate casts were used to investigate the patterns of variation in the epidermal characteristics of the leaves. Stomatal density and epidermal cell density differed between cultivars, but there was no effect of location within each cultivar for either trait. Stomatal density in 'Pawnee’ was intermediate between the two parent cultivars, with ‘Mohawk’ displaying the least and ‘Starking Hardy Giant’ the greatest stomatal density. ‘Pawnee’ had the greatest epidermal cell density while ‘Starking Hardy Giant’ displayed the least, with ‘Mohawk’ being intermediate but distinct from the other two. There were differences in stomatal index between ‘Starking Hardy Giant’ and the other two cultivars at each location with consistent patterns across locations for each cultivar. Although differences in trichome abundance were observed between cultivars, patterns were not consistent across locations. The consistency in the stomatal and epidermal cell densities of a pecan cultivar grown in different locations, coupled with the resolution of differences between cultivars grown at the same location, suggests that these traits may be useful for screening ecotypes for breeding and cultivar development.