Manipulation of shoot growth patterns in relation to early fruit set in ‘Hass’ avocado ( Persea americana Mill.)

Abstract

Shoot tipping and pruning, rootstocks and plant growth regulator applications were evaluated for their potential to change canopy structure and improve productivity of ‘Hass’ avocado. Tipping and pruning were successful in limiting the length of the primary shoot axis and increasing axillary branching, without influencing total fruit set. Trees on the rootstock ‘Velvick’ had greater vigour with a higher ratio of sylleptic to proleptic shoots than trees on ‘Hass’ rootstock. The growth inhibitor Cultar (paclobutrazol) reduced shoot length and leaf size, but had no effect on the number of shoots or on fruit set. The auxin inhibitor TIBA (2,3,5-triiodobenzoic acid) stimulated proleptic axillary shoot growth without effect on fruit set. Cytolin (6-benzyladenine and gibberellins 4+7) increased sylleptic axillary shoot growth and subsequent fruit set, but the timing of application was critical. Manipulation of sylleptic shoot growth may provide the key to improving tree form and productivity in avocado.