Distribution of Indol-3-Acetic Acid (IAA) in the Annual Fruit-Bearing Shoots of Walnut Cultivars 'Franquette' and 'Lara'

The levels of indol-3-acetic acid (IAA) in buds of fruit-bearing annual shoots in cultivars 'Franquette' and 'Lara' were analysed. The aim of the study was to observe differences in IAA content during the growing season, and to determine the spatial distribution of IAA in different sections along the length of the shoots. Monocyclic shoots were divided into four sections (terminal, subterminal, medial and basal) with the same number of nodes. Buds for IAA analysis were collected on four sampling dates: at bud-breaking, at the end of spring elongation of the shoots, at the end of summer elongation, and during winter dormancy. The procedure for preparing samples for HPLC analysis with UV - Vis and fluorescence detectors was a slightly modified method of Kovac et al. (2003). The results showed similar seasonal dynamics with maximum IAA contents at bud-breaking date and during winter dormancy in both cultivars. In 'Franquette', the concentrations of IAA significantly exceeded those measured in 'Lara' at all sampling dates except in July, after the spring elongation. In terminal, subterminal and medial shoot sections we found more IAA in 'Franquette', while in 'Lara', more auxin was found in the basal section of the shoot.