Location: Crop Germplasm Research
Project Number: 6202-21000-035-02
Start Date: Sep 01, 2013
End Date: Aug 31, 2014
Evaluate the performance of 8 open-pollinated rootstock selections chosen to maximize geographical resolution across the Eastern and Western US pecan-growing areas and Mexico. Three of the rootstocks for the study ('Curtis', 'Elliott', and 'Moore') are commonly used in Southeastern US orchards. 'Burkett', 'Riverside', 'Shoshoni', and 'VC1-68' are the most common rootstocks used in the Southwest. The final rootstock in our study, 87MX5-1.7, is a USDA-ARS accession that originates in Mexico and because of its vigor shows great promise for use as a commercial rootstock. In the fall of 2012, seeds collected by the scientist from the USDA-ARS National Clonal Germplasm Repository for Pecans and Hickories in College Station, TX, were planted and grown in Las Cruces, NM, under greenhouse culture in potting media. The seedlings will be transplanted into 10-gallon plastic containers filled with a native Mesilla Valley agricultural soil (which are calcareous but have a lower-than-average lime content for the region). Pots will be randomized into three different soil lime treatments, which represent the range of soil lime content in New Mexico. To reach the target lime content, agricultural lime will be mixed with the soil in the pots at 3 rates. The target lime contents will be: 30% lime ("High"), 15% lime ("Medium"), and no added lime ("Control"). Each soil lime treatment will contain 20 individual replicates within each of the 8 rootstock varieties for a total of 160 seedlings per treatment and 480 seedlings in the study. The rootstocks ability to maintain adequate plant mineral levels over time under each of the treatments will be measured annually through leaf tissue analyses. Horticultural and physiological characteristics important to pecan production will also be evaluated. For example, vegetative vigor will be documented through regular measurements of shoot length and trunk diameter. Photosynthesis will also be measured mid-season with a Li-6400XT portable photosynthesis system. Severity of nutrient deficiency symptoms will be evaluated visually and with a SPAD meter. This study will conclude before the trees go dormant at the end of the second growing season with a destructive whole-tree tissue sampling (leaves, roots, shoots) to evaluate total biomass (dry weight) and total nutrient content of each tree.