Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2007
Publication Date: 9/30/2007
Citation: Ledbetter, C.A., Sisterson, M.S. 2007. Advanced Generation Peach-Almond Hybrids as Seedling Rootstocks for Almond: First Year Growth and Potential Pollenizers for Hybrid Seed Production. Euphytica. 160(2): 259-266. Interpretive Summary: For maximum nut production, almond trees need a deep rooted and vigorous rootstock to support the large unpruned canopy. Peach rootstocks have been used extensively for almond trees because of their ease of propagation and root knot nematode resistance. However, peach rootstocks are lacking in necessary vigor, and the annual tree shaking operation at harvest can damage peach roots, resulting in tree injury or death. We demonstrated that seed from peach-almond hybrids produced seedling rootstocks with much more vigor as compared with standard peach rootstock seedlings. Because of the enhanced vigor, peach-almond hybrid seedlings could be propagated at an earlier date compared to peach rootstocks, resulting in larger finished nursery stock. These results impact both almond tree nurseries and almond growers. An earlier propagation date allows nurseries more days for June-budding almond trees in the spring and a longer growing season, resulting in larger finished trees that increase the nursery’s profit. Almond growers would benefit from using trees propagated on peach-almond hybrids because of the enhanced vigor and better anchored trees.
Technical Abstract: For decades, seedling peaches have been used as the standard rootstock in California almond orchards. Vigorous, deep rooted trees are needed in almond orchards for maximum yields and to withstand the annual tree-shaking at harvest. Currently, researchers are actively evaluating rootstocks for almonds in field trials and in various screening protocols. In this study, seedling rootstocks, obtained from male-sterile peach-almond hybrid mother trees, were compared with ‘Nemaguard’ peach seedlings for emergence in the nursery row, trunk caliper at propagation time and end of season dormant above ground tree weight. Seedling emergence was affected significantly (p<0.05) by seed source, as was trunk caliper and end of season dormant above ground tree weight. Trunk caliper and dormant above ground tree weight were also affected significantly (p<0.05) by planting year. Results obtained in this study demonstrate the enhanced first year seedling growth from peach-almond hybrids, as compared to ‘Nemaguard’ seedlings. Seedling emergence in the rootstock bed was not affected significantly by planting year. Peach-almond hybrid seedlings were ready for June-budding at an earlier date compared to ‘Nemaguard’ seedlings, providing the potential for larger-sized finished nursery stock by the end of the growing season. Due to the male-sterile status of the peach-almond mother trees, bloom periods of several root-knot nematode resistant rootstock cultivars were examined for their degree of synchronicity with the mother trees. The examined rootstocks and mother trees varied in both chill hour and post-chill heat requirements necessary to effect bloom. ‘Flordaguard’ peach rootstock began bloom in advance of the male-sterile mother trees, whereas the bloom period of ‘Tsukuba No. 4’ occurred well after, suggesting they would not be effective synchronous pollenizers for consistent hybrid seed production. Based on more limited flowering period data, better bloom synchronicity was achieved with a Tsukuba No. 4 X Flordaguard hybrid.