2018 ASHS Annual Conference

Pecan (Carya illinoinensis) is native to Mexico and the south-central US, spanning diverse humid to semi-arid environments. The southwestern US is playing an increasingly significant role in pecan production, now comprising nearly 25% of improved US pecan acreage. Suitable climate, low pest and disease pressure, deep soils, and the availability of irrigation water have led to rapid expansion of pecan acreage in the Southwest. Maximizing productivity and profitability requires identification of pecan rootstocks that can thrive in this region’s unique environment. High soil pH and lime content limit soil availability of micronutrients, resulting in severe nutrient deficiencies. In this study we investigated the interactive effects of pecan seedling maternal genotype and soil lime content on nutrient uptake in alkaline soils. We hypothesized that seedlings with western-region maternal ancestry are better adapted to extract nutrients from calcareous, alkaline soils than those with eastern- or southern-region ancestry. Eight maternal genotypes across the native range of pecan were used in this study: eastern-ancestry genotypes (‘Curtis’, ‘Elliott’, and ‘Moore’), western-ancestry genotypes (‘Riverside’, ‘VC1.68’, ‘Shoshoni’, and ‘Burkett’), and one southern-ancestry genotype (‘87MX1.5.7’). The seedlings were grown in 18.5-liter pots under three soil lime treatments, representing the range of soil lime content in the Southwest. Agricultural lime was added to soil at 3 rates: 30% lime, 15% lime, and no added lime (“Control”). Each genotype x lime content combination was replicated 6 times. Trees received 30 g of 16N—3.5P—6.6K fertilizer 6 times annually, but no micronutrient fertilizers were applied. Leaf tissue nutrient concentrations were measured each growing season for 3 years. In 2015, soil lime treatments and maternal genotype had no apparent effect on leaf mineral nutrient levels with the exception of manganese and zinc. Compared with lime-treated seedlings, Control seedlings had 18%, 66%, and 46% higher leaf manganese concentration in 2015, 2016, and 2017, respectively. Seedlings from all maternal genotypes except ‘Moore’, ‘Curtis’, and ‘Shoshoni’ were deficient for zinc (<50 ppm) in 2015. All maternal genotypes were deficient for zinc in 2016 and 2017, however, ‘Shoshoni’ seedlings had 60% and 209% higher zinc concentrations, respectively, compared with other genotypes. These data suggest that maternal genotype influences zinc uptake, but, in most cases, seedlings of western maternal ancestry did not have higher zinc levels than seedlings of eastern or southern maternal ancestry. Additional research is needed to investigate if the same patterns persist in grafted trees and in a field setting.