Hansen Agricultural Research and Extension Center
University of California
Hansen Agricultural Research and Extension Center

Plant Pathology and Landscape Horticulture

Floral Bud Viability of ON-crop Mandarin Trees from December to Full Bloom in Ventura County

Researchers: Carol Lovat, UCRiverside & Ben Faber, UCCE-VC

Correlative inhibition occurs when auxin accumulates and/or cytokinin (CK) concentration is reduced, auxin>>CK. During the on-crop year, correlative inhibition prevents bud break on bearing shoots to a greater degree than nonbearing shoots, reducing growth of summer vegetative shoots and the number of nodes that can produce inflorescences at bloom. Spring bud break on on-crop trees is also inhibited, further reducing return bloom and yield. For on-crop 'Pixie' mandarin trees, nonbearing shoots contribute 10-fold more inflorescences to bloom the following year than bearing shoots. Treating on-crop 'Pixie' and 'Nules' Clemetine mandarin trees with an auxin-transport inhibitor plus a CK to achieve auxin< or whether the expression of critical floral gene/s is irreversibly inhibited during floral development, resulting in buds that are no longer viable. This issue must be resolved to understand whether alternate bearing in mandarins can be mitigated with dormancy-breaking plant growth regulator treatments or necessitates fruit removal prior to a critical point in floral development to successfully increase return bloom and yield. 

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