Location: Crop Germplasm Research
Project Number: 3091-21000-046-010-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2024
End Date: Jul 31, 2025
Objective:
Pecan (Carya illinoinensis) is one of the most valuable nut trees native to North America and is also one of the most salt sensitive tree crops. Salinity is an issue in commercial pecan production and can lead to reductions in pecan yield and nut size in the arid and semi-arid Southwest. Typically, mature pecan trees need between 1300 mm to 1525 mm irrigation water per year, including rainfall. However, in the arid and semi-arid southwestern states, rainfall is limited (e.g. 200 to 300 mm annually in west Texas). Therefore, pecan orchards in these regions are typically irrigated with a combination of surface water and groundwater. However, the salinity of groundwater is usually higher than that of surface water. In recent years, due to drought, pecan growers have increasingly relied on groundwater due to limited surface water supply, resulting in elevated salinity in the soil and noticeable impacts on pecan yield and nut size (communications with growers in west Texas). Due to the long lifespan of pecan trees, commercial pecan orchards use locally adapted rootstock to speed up fruiting time. Rootstock plays a crucial role in pecan orchards, influencing tree vigor, trunk diameter, and canopy size. As such, investigating salt tolerance of these rootstocks is imperative to enhance healthy scion growth and nut size and quality. Salt-tolerant genotypes are often tolerant to drought; however, drought-tolerant genotypes are not necessarily tolerant to salt. In this project, we will investigate 12 pecan genotypes originally from different geographical locations for their salinity. These pecan genotypes include the most common rootstock used, and also some potentially useful rootstocks.
Objectives: The objectives of this study are to 1) evaluate the salt tolerance of the selected genotypes from USDA repository germplasm, 2) characterize the physiological responses of selected rootstocks to salinity stress, and 3) determine if one or more of these selections can be used as productive rootstocks by the U.S. pecan industry.
Approach:
The ARS Pecan group will collect 100 open-pollinated nuts of each of the 12 selections. Among these selections, Elliott, VC1-68, Riverside, Giles, and Moore are being used as rootstocks in the U.S.; Major, Peruque, San Felipe, and Posey have the potential for rootstock use, and 87MX5-1.7, 87MX4-5.5, and 1997-32-005 are breeding lines. 87Mx5-1.7 exhibits vigorous growth, 87MX4-5.5 is tolerant to soil pH 8.2, and 1997-32-005 is a hybrid (Carya x leconti) between EW 7-25 x VC1-68 and can grow in wetlands. ARS will stratify the nuts at cold temperatures for 1-2 months. In late winter, nuts will be germinated in pots in the greenhouse. Based on the seedling growth, uniform seedlings will be delivered to Texas A&M AgriLife Research at Dallas. The cooperator will transplant the seedlings to large containers and place in a greenhouse. Three salinity levels (at electrical conductivity of 1 dS/m, 3 dS/m, and 6 dS/m) plus control will be tested. Experiments will follow a randomized factorial design with salinity as the main plot and genotype as subplot. Data collection will include all growth and morphological parameters, physiological responses, and leaf mineral analysis.
