ARS | Publication request: Variation in anatomical characteristics in leaves of pecan seedstocks from Mexico and the United States

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2011
Publication Date: April 7, 2011
Citation: Sagaram, M., Lombardini, L., Grauke, L.J. 2011. Variation in anatomical characteristics in leaves of pecan seedstocks from Mexico and the United States. Journal of the American Society for Horticultural Science. 136(2):103-108.

Interpretive Summary: Pecan trees are native to North America and are found over a wide range of climates and soils from the northern US to southern Mexico. Over very long periods of time, trees growing in one place may have developed genetic differences that help them in that location. In breeding trees that will do well in particular areas, we need to know which traits are related to improved performance for those regions. We studied leaf structure as it relates to water use efficiency using seedlings grown in a common garden from diverse seed sources. We found that seedlings grown from open-pollinated seed of a common mother (seedstock) were very uniform in the number of stomates and epidermal cells per leaf area. There were very large differences in the number of stomates and the number of epidermal cells between seedlings grown from different seedstocks, especially when seed came from different regions. Trees that originated in dry areas produce seedlings with leaf structures that could contribute to water use efficiency in those areas. This is important as we try to improve water use efficiency in pecan.

Technical Abstract: Leaf anatomical traits of Mexican and U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] seedstocks grown in a single location were studied to determine patterns of ecogeographic variation within the natural range. Stomatal density (SD) was uniform among open-pollinated seedlings of a common maternal parent, with two-fold differences in SD separating some seedstocks. Stomatal density and stomatal index (SI) of Mexican seedstocks were related to longitude and annual precipitation of origin. Stomatal density increased along the longitudinal gradient towards the east coast of Mexico: seedstocks originating from areas on the east coast of Mexico had greater SD than seedstocks originating from the drier areas on the west coast. Stomatal density and SI did not follow a pattern along latitude or longitude in the U.S. seedstocks. A trend in isotopic carbon (13C) discrimination was distinguished in Mexican seedstocks, thus suggesting greater water use efficiency in pecan trees from areas with reduced annual precipitation.