Variation in ecogeographical traits of pecan cultivars and provenances
Pecan [Carya illinoinensis (Wangenh.) C. Koch] is a species distributed over an area of varied geographic and climatic variation in the Unites States and Mexico providing a potential for anatomical and physiological adaptation within the cultivars and provenances (i.e., the area of origin of seed). An assessment of leaf anatomical traits of pecan cultivars (Pawnee, Mohawk and Starking Hardy Giant) collected from three locations (Tifton, GA., Chetopa, KS., and Stillwater, OK.) was conducted to provide an understanding of patterns of ecogeographic variation within the natural range. The stomatal density 'Pawnee? (404 stomata/mm2) was intermediate between that of ?Mohawk? (363 stomata/mm2) and ?Starking Hardy Giant? (463 stomata/mm2). There were differences among the three pecan cultivars at the same location but there were no differences in stomatal density within the same cultivar grown at three distinct locations. The study suggested that differences in stomatal density in pecans are cultivar-specific rather than being determined by environmental factors. The stability of certain leaf anatomical characteristics, such as stomatal density, for pecan cultivars grown at different locations confirms that these traits can be used for screening provenances with desirable leaf anatomical characteristics for breeding and cultivar development. To achieve the objective of studying anatomical, morphological and physiological traits, Mexican and U.S. provenances grown at the Pecan Genetics and Breeding Program facility in Somerville, Texas were used. The prominent results from the provenance study indicate the presence of intra-specific variation in pecan provenances for the morphological and anatomical traits along the east-west gradient. It is also interesting to note that western provenances displayed the least stomatal density (350 stomata/mm2) while an eastern provenance showed the greatest stomatal density (728 stomata/mm2). This trend may be explained with the gradient in moisture availability from the wetter conditions in the east to the arid conditions in the west in North America. Most of the physiological traits measured did not show any distinct differences between the provenances. There is a great possibility that anatomical traits like stomatal density are genetically controlled to a great extent in pecan in comparison to the physiological traits.