Growing Degree Days Effects on Growth and External Quality of Chrysanthemum (Dendranthema grandiflora).

Growing degree day (GDD) is a measure of heat accumulation used to predict growth and development rates of plants to reach certain phenological stages, such as maturity and harvest. Forecasting these stages is widely used in cutting flowers providing information on harvest, yield, plant growth. Data in the literature shows that there is correlation between temperature and flowering period and quality in chrysanthemum, but none of them are related to the effects of GDD accumulation on it. In Brazil chrysanthemum is a valuable commodity in the market and research on GDD may aid growers in the cultivation process. Having this in consideration, our objectives were to evaluate the influence of GDD on growth and external quality of chrysanthemum. Our results shown that there were positive correlations between the numbers of floral structures, flower dry matter, number of opened flowers with the increase of growing degree days. Plant height also increased with GDD accumulation but there was a delay in time to the flower harvest.