Propagation of pinyon pine: topworking Pinus monophylla to Pinus edulis rootstocks

Abstract

Virtually all production of pine nuts from single- and double-leaf pinyon pines (Pinus monophylla Torr. & Frém. and P. edulis Engelm. [Pinaceae], respectively) is by collection from wild tree populations. The high demand for premium nuts, and the adaptability of pinyons to uncultivated lands, would suggest potential for their development as a managed agroforestry crop. Grafting superior nut-producing accessions to existing trees could enhance production similar to that found when established apple orchards are topworked to a superior cultivar. Using unirrigated P. edulis trees as rootstocks, we explored the feasibility of grafting mature P. monophylla scions to them. We evaluated the impact of scion accession, scion preparation, grafting method, and crown pruning on topwork grafting success. We found that grafting scions with both needles and buds was more successful than scions with buds alone. Sidewedge grafting was found to be more successful than bark grafting; however, we found no statistical difference in the success of side-wedge or side-veneer grafting techniques, with both approaching 80% success initially before declining with time. We found differences in grafting success due to accession, but not to crown pruning. While these results indicate that mature pinyons can be successfully topworked, further research is needed to determine if nut production can be increased and to determine the cultural practices required to convert the entire upper portion of the rootstock tree to the scion.