Effect of assimilate availability on flower characteristics and plant height of cut chrysanthemum: an integrated study

The influence of assimilate availability on the number of flowers per plant, individual flower size and plant height of chrysanthemum was investigated in different seasons, integrating the results from eight greenhouse experiments. Increased assimilate availability was obtained by higher light intensity, higher CO2 concentration, lower plant density or longer duration of the long-day (LD) period. Within each experiment, conditions that were expected to increase assimilate availability indeed resulted in higher total dry mass of the plant, excluding roots (TDMp). In contrast, flower mass ratio was hardly affected, except for the increased duration of the LD period that significantly reduced the partitioning towards the flowers. Consequently, an increase in total flower dry mass with assimilate availability was observed and this was mainly a result of higher numbers of flowers per plant, including flower buds (NoF). Individual flower size was only influenced by assimilate availability when average daily incident PAR during short-day period was lower than 7.5 mol m(-2) d(-1), resulting in lighter and smaller flowers. Excluding the positive linear effect of the duration of the LD period, assimilate availability hardly influenced plant height (<10% increase). It is concluded that within a wide range of growth conditions chrysanthemum invests additional assimilates, diverted to the generative organs, in increasing NoF rather than in increasing flower size. Irrespective of the growth conditions and season a positive linear relationship (r(2) = 0.90) between NoF and TDMp was observed. This relationship was cultivar-specific. The generic nature of the results is discussed.