Spur leaf and fruitlet seed phytohormones of biennial apple trees affect return bloom

Application of thinning agents to maintain consistent flower production, fruit quality and yield of biennial bearing apple cultivars is a practice adopted by apple growers.
Fruitlets are known to repress flowering buds, thus reduce fruit formation the following season.
Conversely, the presence of spur leaves adjacent to buds can stimulate floral development.
Previous studies have investigated compounds associated with floral induction (FI), when signals are believed to be received by vegetative buds to trigger flower development.
These compounds include plant hormones such as cytokinins, salicylates as well as chlorogenic acid and its derivatives.
However, related pathway metabolites in other plant tissue have not been investigated.
Metabolomics profiling was undertaken to identify potential promotors and repressors in leaves and fruitlets in ‘Ruby Matilda’ apple trees during the FI phase of flower meristem development.
Different crop load levels were imposed to individual leaders of bi-axis trees.
Leaf and fruitlet samples were collected at 60 days after full bloom.
The presence of metabolites from the cytokinin pathway, including inosines, adenosine and its derivatives were found in leaves and fruitlet seeds.
Unlike fruitlet seeds, the presence of leaves stimulate flower formation suggesting that the cytokinins present in leaves are likely translocated to buds during floral induction.
The involvement of leaves and fruitlet seeds, takes into consideration the importance of site of action and mechanism of applied thinning agents on plant tissue.

II International Symposium on Precision Management of Orchards and Vineyards

P. Reddy, T. Plozza, A. Scalisi, J. Hemsworth, D. Ram, M. Peavey, L. McClymont, V. Ezernieks, I. Goodwin, S. Rochfort

biennial bearing, bud, chemical signalling, Malus domestica Borkh, metabolomics, ‘Ruby Matilda’

https://doi.org/10.17660/ActaHortic.2024.1395.40