Genotypic variation in the response to suboptimal temperature at different plant densities in cut chrysanthemum

Energy efficiency of greenhouse cut chrysanthemum (Chrysanthemum morifolium Ramat.) may be increased by breeding. In addition to breeding for cultivars with a shorter reaction time at suboptimal temperatures, an alternative approach would be to develop cultivars that are heavier at suboptimal temperatures so that they could be grown at a higher plant density, enhancing the production per unit area. Therefore, the combined effect of temperature and plant density on growth and development of four cut chrysanthemum cultivars was investigated in three greenhouse experiments, carried out in different seasons. For growth-related traits, no interactions between temperature and cultivar were found, limiting the possibilities for breeding. At suboptimal temperatures, growth rate early in the cultivation period decreased as a consequence of a lower light interception resulting from a lower specific leaf area. Thus a higher dry mass production at lower temperature could only be explained by a longer cultivation time. Temperature also influenced external quality, but these effects were cultivar dependent. For instance, temperature affected the slope of the positive linear relationship between total dry mass and number of flowers, reducing number of flowers at low temperature for the same plant dry mass. It is concluded that there are possibilities for breeding for suboptimal temperature-tolerant cultivars.