The Effects of Auxin, Gibberellins, and Defoliation on the Expression of Apple Flowering Genes (Malus xdomestica Borkh.)

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 plant growth regulators and defoliation treatments affect flowering. It is assumed this effect is preceded with a change in gene expression. MdTFL1 is a key gene involved in flowering repression, however MdFT1 promotes apple flowering. The interaction between PGRs and the floral initiation pathway is a key player to increase our understanding of apple flowering. In this study we are trying to understand the effect of exogenous applications of gibberellins and auxin, and defoliation treatments on the expression of MdFT1 and MdTFL1 genes and subsequent flower formation. We hypothesized that local application of gibberellins or defoliation will inhibit flowering, while local application of auxin will stimulate flowering. The inhibiting or stimulating effect will happen in response to increase or decrease in MdFT1 and MdTFL1 gene expression levels. We tagged bourses on Honeycrisp apple trees, and randomly applied gibberellins, auxin or defoliation treatments. These treatments were applied locally at times previously shown to inhibit (gibberellins and defoliation) or stimulate (auxin) flowering. Samples were collected throughout the growing season to study the change in flowering gene expression and flower formation. Different treatments showed different flower formation levels. Both local defoliation and gibberellin treatments showed lower flowering formation compared with auxin and control treatments. Results of the effect of different treatments on MdFT1 and MdTFL1 genes using Quantitative PCR technique are being processed and will be presented.