Project Number: 6202-21000-032-04
Project Type: Specific Cooperative Agreement

Start Date: Jul 01, 2006
End Date: Jun 30, 2009

Objective:
Screen for improved water use efficiency (WUE) in pecans within an orchard that represents provenance variation.

Approach:
The experiment will be conducted at the provenance orchard located in the USDA-ARS facility at Somerville, Texas. A total of 15 pecan provenances will be studied for anatomical and physiological characteristics. Microscopy: To determine the density of stomata and epidermal cells within the leaves of a plant, a portion of the bottom side of the first set of leaflets from the terminal leaf will be painted with clear nail polish. After allowing the nail polish to dry for 10-15 minutes, the acetate cast will be stripped using clear packing tape and placed on microscope slides. Epidermal cells and stomata will be counted from each cast under an optical microscope at 200x. Ten counts will be made from each cast for use in the analysis. Data will be recorded and analyzed for stomatal and epidermal cell density in that section of the leaf. Gas exchange studies: Single leaf gas exchange and chlorophyll fluorescence will be investigated. An open infrared gas exchange system (Mod. 6400, LICOR, Lincoln, NE) with an integrated fluorescence head (Mod. 6400, LICOR, Lincoln, NE) will be used to calculate single leaf net CO2 assimilation rate (A), transpiration rate (E), stomatal conductance (gs) and photochemical efficiency (Fv/Fm) will be determined. The ratio of A/E will provide an additional approach to determine the WUE of the plant. Carbon-13 isotopic discrimination: Three 15-cm long twigs per tree will be collected from the previous season shoots in February 2006. The twigs will be debudded, cut in 2-3 cm long sections, dried at 70ºC for 72 hours, ground to pass through a 40 mesh screen on the a Wiley Mill and analyzed for 13C content and 13C discrimination.