BUD ORIENTATION ON HORIZONTALLY TRAINED CANES MODIFIES BUDBREAK AND SHOOT FRUITFULNESS OF ACTINIDIA DELICIOSA 'HAYWARD' VINES

Consistent spring budbreak is an important aspect of regular annual cropping in kiwifruit. In regions with insufficient winter chilling, hydrogen cyanamide is commonly applied to promote even and high budbreak; however, use of this chemical is being phased out around the world because of toxicity concerns. In the absence of hydrogen cyanamide, understanding the factors influencing budbreak and the development of individual shoots is central to creating pruning systems that optimise productivity. To elucidate the effect of bud orientation on budbreak and floral shoot production in ‘Hayward’ kiwifruit, buds were selectively excised from canes based on their orientation (top, side, or bottom), and the behaviour of the remaining buds was compared with that of buds on unmodified control canes. The orientation of buds influenced the percentage budbreak of canes. Buds with a downward orientation had lower budbreak and broke later than those with an upward orientation. When upward-orientated buds were removed, percentage budbreak of downward-orientated buds increased, and they began budbreak earlier. The number of inflorescences per shoot was also altered by bud orientation. Shoots that developed from more upward orientations had greater numbers of inflorescences than shoots that developed from downward-orientated buds. With regard to budbreak and the production of floral shoots, a hierarchy of bud orientation appears to exist within a cane, from top to side to bottom.