ASHS 2024 Conference

Can Hedge-Pruning Reduce Water Needs In Southeastern United States Pecan Orchards? - Bailey Rayfield
Leaf Anatomical Traits and Water Use Efficiency in Four Pecan Cultivars - Sarahi Bracamontes
Performance of Five Early-harvest Pecan Cultivars in South Georgia - Patrick Conner
Enhancing Pecan Tree Resilience Against Spring Freeze Events: Insights from Secondary Bud Dynamics and Carbohydrate Analysis - Lu Zhang
Biochar in Pecan Orchards: Unraveling Water Stress Dynamics for Sustainable Irrigation Management - Jamin Miller
Evaluating Soil Management Impacts on the Pecan Orchard Mycobiome in the Semi-Arid Southwestern United States - McKenzie Stock

Pecan (Carya illinoinensis) trees have experienced higher density plantings which enhances the need for better water use efficiency to increase the sustainability of the orchard. The implementation of hedge-pruning allows for better light penetration as well as more efficient water use in the humid climate of the southeastern United States. The objectives of this study were to determine if irrigation rates can be reduced on hedge-pruned pecan trees with no loss in pecan yield or nut quality. The study is a split-plot design with pruning serving as the main plot effect and irrigation serving as the split plot effect. On hedge-pruned trees, all growth beyond 8’ from the trunk on the East side of the tree was pruned in year 1 and on the West side of the tree in year 2. Trees were topped on each side in their respective years at an angle with a peak at 40’. No pruning will be done in year 3. Hedging treatments are arranged in three tree blocks with each irrigation treatment occurring once per block as follows: 1) 100% irrigation; 2) 50 % irrigation; 3) non-irrigated control. Hedged blocks were replicated four times, and the non-hedged blocks were replicated three times. Among the irrigation regimes, there was no statistical difference between treatments indicating that, under the environmental conditions observed, less water is sufficient for pecan production, regardless of pruning treatment. Although, there has been no improvement in yield from the hedge-pruned trees, percent kernel has increased in the hedged trees compared to the non-hedged trees, suggesting an enhancement of pecan nut quality with hedge pruning.

The leaf surface and interior structure can affect photosynthesis and transpiration rates associated with water use efficiency. Several studies have assessed pecan (𝘊𝘢𝘳𝘺𝘢 𝘪𝘭𝘭𝘪𝘯𝘰𝘪𝘯𝘦𝘯𝘴𝘪𝘴) leaf anatomical traits and established differences between cultivars; however, the effect of these traits on water use efficiency across cultivars has not been established. Understanding the relationship between leaf anatomical structures and water use efficiency across pecan cultivars allows for the identification of those that are well suited for water limited environments. In this study, we examined the leaf mesophyll layer thickness (µm), trichome density (trichome mm⁻²), stomatal density (stomata mm⁻²), and stomatal pore area (µm²) of four pecan cultivars (‘Wichita’, ‘Western’, ‘Pawnee’, and ‘Lakota’; all grafted to clonally propagated rootstocks). Leaves were collected at the NMSU Leyendecker Plant Science Research Center, and their cross-section and abaxial surface were imaged using light and scanning electron microscopy, respectively. ‘Lakota’ leaves had the thinnest palisade mesophyll layer and thickest spongy mesophyll layer relative to total leaf thickness. The stomatal density of ‘Pawnee’ was significantly less than the other cultivars, but no significant differences in stomatal pore area were observed. Intrinsic water use efficiency, calculated as ratio of the carbon assimilation rate to stomatal conductance to water vapor, was obtained using a leaf gas exchange meter on three separate days. A stable carbon isotope composition analysis was also conducted to provide insight into the leaf’s longer-term water use efficiency. The results showed that the intrinsic water use efficiency of ‘Lakota’ was different from ‘Western’ on one of the days; however, differences between cultivars were not significant when averaged across the measurement dates. Furthermore, the relative ¹³C abundance and ¹³C discrimination did not have significant differences across the four pecan cultivars evaluated, suggesting that differences in leaf anatomical traits did not influence the water use efficiency of these samples.

Five pecan (Carya illinoinensis) cultivars were evaluated over 15 years in a trial at Tifton, GA, USA. Trialed cultivars included the standard early cultivar Pawnee, and the more recent releases Byrd, Morrill, Lakota, and Treadwell. Actual yield were measured for each tree each year and a 50-nut sample was taken to determine nut quality. Trees were evaluated for leaf and nut scab infection (Venturia effusa) and black aphid (Melanocallis caryaefoliae) damage. ‘Pawnee’ yielded significantly less than all the newer cultivars which had similar cumulative yields. However, ‘Byrd’, ‘Lakota’, and ‘Treadwell’ had significantly more yield alternation than ‘Pawnee’ and ‘Morrill’, with reduction of nut quality in the “ON” years. ‘Pawnee’ was the earliest cultivar and produced excellent quality nuts, but yields were mediocre. ‘Lakota’ had excellent scab resistance, but overcropped resulting in inferior quality, and should only be grown in orchards were crop loads are controlled by hedging or tree shaking. ‘Byrd’ and ‘Treadwell’ are very scab susceptible and also need crop load control, making them poorly suited for south Georgia. ‘Morrill’ had consistent cropping and excellent nut quality but is also very scab susceptible and should only be grown with excellent disease management practices.

Pecan growers face significant challenges in protecting their crops from the spring freezes that devastate yields. Conventional freeze protection methods are impractical for the large, tall trees. This study investigated the dynamics of the secondary bud break in pecan trees, a mechanism that ensures yield when primary buds are damaged. In three pecan cultivars ('Pawnee,' 'Kanza,' and 'Maramec') we characterized the sprouting potential of secondary buds after the primary buds were cold damaged. Primary bud shoots were collected at three different bud growth stages: outer bud scale shed stage, inner bud scale shed stage, and early bloom stage. The shoot samples held at 6°C to terminate primary buds’ growth. The cold treated shoots were then held in growth chambers set to mimic spring humidity, temperature, and light conditions. The percentage of branches with secondary bud break was recorded. The carbohydrate levels (sugar and starch) were measured in the apical shoots treated at the outer bud scale shed stage. The results showed variation among cultivars in the number of shoots with secondary buds and the stage at which primary buds were terminated. The ‘Kanza’ and ‘Pawnee’ cultivars produced more secondary buds when the primary buds were cold damaged in the outer bud scale shed stage. The ‘Maramec’ cultivar produced more secondary buds when the primary buds were cold damaged in the inner bud scale shed stage. The A carbohydrate analysis of the three cultivars demonstrated a correlation between successful secondary bud break and elevated carbohydrate levels in the one-year-old shoots. Cultivars with higher secondary bud break rates, 'Kanza' and 'Pawnee', had higher carbohydrate levels than 'Maramec.' These findings suggest that higher carbohydrate levels in one-year-old shoots facilitate successful secondary bud break following spring freeze damage to primary buds. This research suggests developing production practices to improve tree carbohydrate levels in the late summer and fall could potentially protect pecan production from spring freeze damage.

Pecan orchards in the southwestern United States face significant challenges due to persistent drought conditions that adversely affect yield and nut quality. Pecans are recognized as the most water-intensive crop in the region, and therefore require innovative strategies to optimize the available irrigation water. This study explores the use of pecan wood-derived biochar as a soil amendment to enhance the soil water-holding capacity and alleviate water stress in pecan orchards. We conducted field experiments during the summer of 2023 in a flood-irrigated pecan orchard located in the Mesilla Valley, New Mexico, USA. We accounted for the irrigation gradient in a flood-irrigated orchard by using a randomized complete block design with four blocks, each containing three equidistant trees from the irrigation valves. The trees within each block were randomly assigned to one of three biochar application rates: 0 kg/ha (treated area), 6300 kg/ha, and 12600 kg/ha. The treated area was situated within the herbicide strip, spanning 9.14 m in length – centered on the tree – with 1.22 m on either side of the tree. To assess tree water status, two leaf samples from the lower shaded canopy were covered in aluminum foil bags for a minimum of 15 minutes before mid-day stem water potential was measured. Mid-day stem water potential was measured throughout the growing season near the end of each irrigation dry-down cycle. For each tree, we calculated the average mid-day stem water potential and then performed an ANOVA to compare the averages across the treatment groups. In the five months after biochar application, there were no significant differences in tree water status across the treatment groups. This highlights the need for more research to study the interactions among soil moisture content, biochar amendment applications, and pecan tree mid-day stem water potential. This study contributes to the ongoing discourse that calls for enhancing crop water use efficiency in arid regions by providing a foundation for future studies that seek to use biochar as a sustainable agricultural practice in pecan orchards.

Pecans hold significant agricultural importance in the water-limited Southwestern United States, underscoring the need for sustainable soil management practices in pecan cultivation. Recognizing the intricate relationship between soil treatments and the soil microbiome is essential to develop effective orchard soil management strategies. Soil fungi, particularly root-associated mycorrhizal fungi, are vital in facilitating water and nutrient uptake, protecting against pathogens, and enhancing overall orchard health and productivity. Soil management may impact the fungal community composition of Southwestern pecan orchard soils. Various soil management strategies are implemented in pecan orchards, including varying soil cover or applying mycorrhizal and bacterial inoculants. These techniques alter the soil environment, which may change the soil fungal biodiversity. This study investigates the impact of diverse soil management techniques on the soil mycobiome within a twelve-year-old ‘Pawnee’ pecan orchard in New Mexico. In a randomized complete block design, eight treatments of various soil cover – bare soil, cover crops, compost, or a combination of cover crops and compost – each either with or without mycorrhizal and bacterial inoculants, were applied to evaluate their effects on soil fungal diversity. Laboratory analyses, including DNA extraction, PCR amplification, and Illumina sequencing, were performed, alongside physiochemical testing for soil pH, electrical conductivity, and mineral nutrient content. The resulting sequence data were analyzed to provide insights into the complex interactions between soil management practices and microbial communities. Sampling conducted during the 2022 Spring and harvest seasons revealed significant differences in alpha and beta diversity between roots and bulk/rhizosphere soil (P < 0.10). Significant differences in alpha and beta diversity of fungi based on treatment were also observed, highlighting the potential influence of soil management practices, including soil cover and inoculant use, on fungal community composition. Our study offers valuable insights into the temporal changes in the community structure of pecan orchard fungi when treated with different soil amendments. Understanding how soil management practices influence the soil mycobiome can inform more sustainable pecan cultivation practices. By optimizing soil management strategies to support beneficial fungal communities, growers may enhance soil health, water and nutrient availability, and plant resilience to environmental stress.

A forum for discussion of potential collaborations with regards to fruit, vegetable, and edible crops – i.e. citrus, breeding, production systems, postharvest, pomology, crop management, viticulture, etc.