Submitted to: Society of America Plant Growth Regulator Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 15, 2003
Publication Date: December 15, 2003
Citation: Tworkoski, T. 2003. Morphological and hormonal relationships in shoots of pillar and standard peach trees. Society of America Plant Growth Regulator Proceedings. 30:190 Technical Abstract: Fruit tree canopy size and shape are managed genetically and culturally to enable high density plantings and to facilitate orchard operations such as pest control. In peach trees (Prunus persica) different canopy shapes can be attained with scions of genetically-selected tree growth habits when grafted to seedling rootstock. Scion of Pillar peach tree growth habits have narrow canopies that may be amenable to high density plantings. Research is being conducted to determine relationships between morphological characteristics and auxin and cytokinin quantities in shoots of Pillar and Standard peach trees. Pillar and Standard ('Harrow Beauty') peach scion was budded to seedling rootstock and planted at the Appalachian Fruit Research Station in Dec. 1998. Bud break and growth components of 1-yr-old stems were measured on 28 March 2002. Branch angle and current-yr growth was then measured during the 2002 growing season. Auxin and cytokinin concentrations were measured in current-yr growth during the 2003 growing season. For auxin analysis, samples were extracted overnight with 80% methanol (fortified with stable isotope of indole-3-acetic acid as internal standard), dried, separated against ethyl acetate (pH 8, retaining aqueous phase), slurried with PVPP, decanted, separated on C18 (pH 3) columns, methylated with ethereal diazomethane, and quantified by gas chromatography-mass spectrometry (GC-MS), correcting for losses with the internal standard. For cytokinin analysis, samples were extracted overnight with 80% methanol (fortified with stable isotopes of trans-zeatin, isopentenyladenosine, dihydrozeatin, isopentenyladenine, trans-zeatin riboside, dihydrozeatin riboside, and trans-zeatin-9-glucoside as internal standards), dried, digested with acid phosphatase (EC 18.104.22.168) to convert nucleotides to nucleosides, loaded to a strong anion exchange column in series with a C18 column, eluted from the C18, loaded to strong cation exchange column (pH 3), eluted with 2 M ammonia in methanol, permethylated with dimethylsulphinyl carbanion and quantified by GC-MS, correcting for losses with the internal standards. As the 2002 season progressed, growth characteristics in Pillar and Standard trees appeared to be associated with hormone differences. Similar bud break patterns indicated weak apical dominance within a 1-yr-old shoot of either growth habit. However, slower growth rates and longer distances from terminal buds to first sylleptic branch indicated a hormone-mediated apical control in Pillar trees. Orthotrophic growth also suggested an auxin-mediated response while delayed senescence may indicate a cytokinin effect as the growing season progressed. In 2003, no difference in auxin concentrations occurred in either growth habit early in the season but greater shoot auxin concentrations were found in Pillar than Standard trees as the season progressed. This supports the finding of weak apical dominance at bud break but more pronounced apical control (e.g. more orthotrophic growth and less sylleptic growth) in Pillar than Standard trees as the season progressed. Lower cytokinin/auxin ratios in Pillar shoots may have contributed to reduced sylleptic growth. Currently, research is being conducted to compare genotypes and establish the management practices for high density Pillar peach tree plantings. Effects of some practices (e.g. pruning) on growth and hormone relationships will be determined to help devise management techniques.