Influences of rootstocks on scion growth in a replicated test orchard

Authors: Wang, Xinwang; Kubenka, Keith; Hilton, Angelyn; Tondre, Braden; Chatwin, Warren; Pisani, Cristina; Bock, Clive; HEEREMA, RICHARD - New Mexico State University; RANDALL, JENNIFER - New Mexico State University

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The pecan, a native North American nut tree, has a wide range of growth spanning various latitudes and longitudes. However, due to its long vegetation period, grafting is necessary to establish the scion on a rootstock and expedite its flowering and fruiting. Unfortunately, choosing an appropriate rootstock capable of adapting to all pecan-growing regions is difficult due to various factors including climate, soil types and environments, and scion-rootstock interactions. Pecan growers are forced to use open-pollinated nuts as seedstock since micropropagation technology is not available. Most pecan seedstocks require dormancy breaking, but the effect of stratification or freeze on seedling growth remains unclear. This research established the impact of different rootstocks on scion growth over years, and provides valuable information for rootstock selection for use by pecan growers.

Technical Abstract: The pecan tree (Carya illinoinensis) is native to North America and is distributed over a wide range of latitudes and longitudes. To accelerate flowering and fruiting of scions, grafting onto an established rootstock is necessary. However, it is challenging to breed or select an appropriate rootstock that is adapted to all pecan growing areas where multiple, varying factors affect the tree. Since micropropagation technology is not readily available for pecan, open-pollinated nuts are used as seedstock. Breaking nut dormancy is required for most pecan seedstocks, but the effect of stratification or freeze on seedling growth is unclear. To investigate the effects of different rootstocks on the growth and development of 'Pawnee' scion, we conducted an experiment using 12 rootstocks from different geographical regions. Open-pollinated seeds were collected and subjected to different treatments: frozen/not frozen and stratified/not stratified. The test was conducted in a randomized complete block design with 240 trees and 5 replicates in each block; data was collected on several growth parameters for three years. The results showed that frozen nuts significantly increased certain growth habits of germinated seedlings but did not affect others. No seedling growth characteristics of stratified nuts changed. The influence of rootstocks on scion growth depended on genotype and origin. Southern rootstocks generally performed better than northern ones, with rootstocks from Mexico significantly increasing scion trunk diameter, plant height, and canopy width of seedlings. Among the 12 rootstocks tested, use of the three southern provenances showed the greatest increase in scion growth parameters, while use of northern provenances resulted in significantly delayed bud break. 'Posey', a northern provenance, was found to significantly increase scion leaflet size compared to other northern provenances. These findings provide valuable insights for rootstock selection and breeding goals in the breeding program.