Regulation of Flower Formation and Alternate Bearing in Apple (Malus × domestica Borkh.)
Apple fruit production is highly dependent on flowering frequency. Irregular flowering leads to biennial bearing. Understanding different factors affecting flower formation in apple is essential to overcome biennial bearing, and to ensure successful annual production of some high value cultivars that show the biennial bearing phenomenon such as ‘Honeycrisp.’ In these studies, we investigated the effect of fruit number per tree and per spur, fruit weight and seed number on ‘Honeycrisp’ flower formation. In addition, we studied the effect of different combinations of defoliation and fruiting treatments on flower formation of two different cultivars with different bearing habits: ‘Honeycrisp’, a biennial cultivar, and ‘Gala’, an annual cultivar. Moreover, we examined the effect of single fruit per spur on spur quality, leaf gas exchange parameters and flower formation of six different apple cultivars varying in their bearing habits. Furthermore, we explored the effects of local gibberellins, auxin and defoliation treatments on both local flower formation and the expression level of MdTFL1 and MdFT1, 2. Our data suggest that apple fruiting spurs are semi-autonomous organs, as flower formation is related to the availability of resources within the spurs and within the whole tree. Hence, fruit number per spur and per tree, bourse leaves’ stomatal conductance and transpiration, and bourse length correlate negatively with flower formation. Moreover, GA 4+7 and defoliation inhibit flower formation, as GA 4+7 upregulated MdTFL1 and defoliation downregulated MdFT1, 2. On the other hand, bourse leaves play a major role in affecting flowering, presumably by both producing and transporting flower formation signals. Moreover, thinning apple spurs to single-fruit per spur could overcome the local inhibition effects of fruiting and reduce biennial bearing.
Hirst, Purdue University.
Off-Campus Purdue Users:
To access this dissertation, please log in to our