Levels of indole-3-acetic acid in vigorous and genetic dwarf apple trees

Seasonal levels of indole-3-acetic acid (IAA) present in buds, meristematic tissues, and leaves of 1-year-old shoots of two selections (vigorous and dwarf) of a F₂ generation apple population with original “Goldspur” × “Redspur” parentage were determined using gas chromatography—selected ion monitoring—mass spectrometry (GC-SIM-MS) with a¹³C-IAA internal standard. A comparison of IAA levels through one growing season was made in the shoots of two trees differing in growth. The levels of IAA in the leaves of the vigorous tree were higher in the early and late growing seasons, as compared to those in the dwarf tree. Levels of IAA in buds of the dwarf tree shoots were found to be higher than in those of the vigorous tree shoots. On leave from Indian Institute of Horticultural Research, Bangalore-560080, India.