Rootstock impacts on 'USDA-ARS-Pawnee' pecan growth, physiological traits, and soil microbial communities

Xinwang Wang^1*Keith Kubenka¹Warren Chatwin¹Angelyn Hilton¹Braden Tondre¹Tingying Xu²Lu Zhang²

• ¹Southern Plains Agricultural Research Center, Agricultural Research Service (USDA), College Station, United States
• ²Oklahoma State University, Stillwater, Oklahoma, United States

Pecan (Carya illinoinensis), native to North America, is the most commercially important species within the Carya genus. Central to nut production across the southern United States, pecans are cultivated for their premium-quality nuts used in various culinary applications. The increasing global demand for pecans has emphasized the need for improved cultivation practices to ensure both economic viability and sustainability. This study examined the impact of 12 different rootstocks on the growth and physiological characteristics of the 'USDA-ARS-Pawnee' scion across multiple years. Key traits assessed included budbreak timing, tree morphology, leaf size, leaf retention, photosynthesis, leaf nutrient content, and soil microbial community composition. Significant differences in budbreak timing were observed among the rootstocks, with northern rootstocks, particularly Peruque, exhibiting the latest budbreak, while eastern rootstocks showed the earliest. Regarding tree growth, southern (Mexican) rootstocks significantly outperformed northern rootstocks in terms of scion plant height, trunk diameter, and canopy width. Rootstocks from the southern regions demonstrated superior growth, highlighting the potential for selecting Mexican rootstocks to enhance pecan tree size in orchards. Leaf size showed variation across rootstocks, with northern and eastern rootstocks producing larger leaves, although these differences were not statistically significant. Lager leaf is positively correlated with higher photosynthesis rate (PSR) and water use efficiency (WUE). 'Giles' (northern) and 'VC1-68' (western) had the highest PSR and WUE, while Elliott (eastern) exhibited the lowest PSR and WUE. Leaf retention did not differ significantly across rootstocks, but northern and eastern rootstocks retained more leaves into early November compared to southern and western rootstocks. Nutrient analysis revealed that most leaf nutrients varied across the 12 rootstocks but were not significantly influenced by rootstock origins. 'Riverside' had the highest Zn content, while 'Peruque' had the lowest. Similarly, 'Major' exhibited the highest B content, and 'Frutoso' had the lowest. Soil microbial analysis revealed differences in microbial composition between the rootstocks, with 'Peruque' promoting ectomycorrhizal fungi and 87MX5-1.7 supporting nitrogen-fixing bacteria, indicating that rootstocks can influence soil microbial diversity and nutrient cycling. These results highlight the importance of rootstock selection for improving tree vigor, photosynthetic efficiency, and soil health in pecan orchards.