Gene expression profiling of candidate genes for flowering initiation and dormancy breaking in Rhododendron simsii hybrids.

The last decade the Belgian florist azalea sector suffered increasingly from inferior flowering quality. The production scheme of azalea is complex and therefore it was difficult for growers to point out the exact cause for the problem. The impact of plant growth regulators on flowering and the need for a cold period to release dormancy have been investigated. An integrated approach that combined physiological measurements and gene expression of candidate genes was applied in two different stages of azalea growth. The impact of day length conditions together with plant growth regulators on the flower initiation revealed that azalea is a day-neutral plant. Application of growth regulators speeds up the flower initiation and the expression of an FT-like gene, one of the signalling molecules in this process. The expression of LFY appears to be indicative for the start of the flower differentiation process. The increased LFY expression can be measured prior to the microscopic confirmation of flower bud initiation. Florist azalea flower buds have a dormant stage and require a period of cold to release it. The expression profiles of ELIP, ARP and dehydrin revealed that dormancy was released after 4 to 5 weeks at 7°C. This was confirmed in a bio-assay. The expression of SUSY and a-amylase confirmed that cold treatment has a negative impact on the starch concentration in the plant which can have serious drawbacks on anthesis.