Molecular Bases of Apple Flowering Inhibition By Defoliation and Gibberellins

Flowering plays an important role in the apple industry. There are many issues associated with apple flowering especially with some high value cultivars such as Honeycrisp. It has been well established that gibberellins and defoliation treatments can inhibit flower formation. Such inhibition is likely preceded by changes in gene expression.

In this study we are trying to understand how local gibberellins, and defoliation treatments inhibit flower formation. We hypothesized that local application of gibberellins or defoliation treatments inhibit flowering via altering the expression of the genes MdFT1 and MdTFL1.

Exogenous gibberellins and defoliation treatments were applied to bourses on Honeycrisp apple trees at times previously shown to inhibit flower formation. Samples were collected throughout the growing season to observe flower formation and to investigate the change in MdTFL1 and MdFT1 gene expression.

Both local defoliation and gibberellins treatments inhibited flower formation. Quantitative PCR was used to measure the effect of different treatments on MdFT1 and MdTFL1.  Results showed that both genes had lower expression levels in response to defoliation treatments, and increased their expression levels in response to gibberellin treatment. This increase in MdFT1 and MdTFL1 expression level in response to local gibberellins treatments associated with inhibition of local flower formation could be an indication that gibberellins inhibit flower formation in apple by inhibiting genes downstream of MdFT1.