Influence of temperature on bud break, shoot growth, flower bud atrophy and winter production of glasshouse roses

<p>The influence of temperature in the range 15-22 °C on growth, production, quality and flower bud atrophy ('blindness') of the rose cultivars Sweet Promise and Varlon was studied. The roses were grown in Dutch glasshouse soil under natural light conditions and studied from October until May during 7 successive years. The influence of the distribution of the air temperature between day and night was studied. Besides the usual night-lower-than-day-temperature regime, also the reverse situation was studied. 'Models' were constructed for: bud break, development time from bud break until harvest, shoot and flower bud weight, shoot length, the length, width, volume and freshweight of the flower bud during harvest and the diameter of shoot and neck, in relation to date of bud break and mean daily temperature during shoot growth.<p>Complementary studies including roses of the cv. Sweet Promise grown in transferable containers were performed in glasshouses and in growth rooms (Phytotron). In these experiments the interaction of temperature and shoot stage with the development time of a shoot, with shoot weight and with shoot length was studied. Shoot weight showed a clear interaction with temperature if night temperature was higher than day temperature. Various shoot stages showed a different sensitivity to temperature with respect to the formation of flowerless ('blind') shoots. A low night temperature during the period cut until shoot elongation (=4cm) decreased blindness, but increased blindness when given in the next period until the flower bud is clearly visible. Higher night temperatures than those commonly used increased production by decreasing the percentage of blind shoots.<p>At a given daily mean temperature an increase in night temperature showed no significant influence on bud break and development time of a shoot but fresh shoot weight and shoot length are significantly reduced, if night temperature increases above day temperature. The mean temperature and the mean irradiance during shoot growth could account for 98 % of the variation in the relevant 'models' when analysed by linear regression analysis. Adding the variable 'relative humidity' to the regression equation explained 97 % of the variation in shoot weight. To explain 87 % of shoot length the variable 'Weight of the Parent shoot' and the square of the temperature had also to be introduced.<p>Heavy parent shoots produced heavier daughter shoots than light parent shoots. The difference in fresh weight for daughters of heavy parent shoots compared to those of light shoots decreased in autumn and increased again in spring. If light intensity decreased in autumn, less light was used to produce one gram fresh shoot weight, while under increasing light intensities more light was used.<p>Fresh weight production per shoot per day increased with temperature for the cultivar Varlon and as a consequence, the amount of light needed per gram fresh weight decreased. In the period December until the middle of March 'Sweet Promise' showed another, reversed, situation: fresh weight production decreased with temperature. This was caused by the fact that 'Sweet Promise' was weakened more by a raise in temperature than "Varlon'. Production in number of flowers and in grams fresh weight per shrub showed a positive linear correlation with temperature for both cultivars.<p>The course of bud break and harvest was studied for 9 night/day temperature combination. A lower temperature resulted in delayed bud break and production.<p>The research made it clear that it is possible and profitable to control temperature on the basis of the daily mean temperature or the temperature sum during bud break and shoot growth, instead of in the orthodox way with a fixed night-lower-than-day temperature regime. Practical applications of the results are given for commercial rose growing. Heating glasshouses on a basis of a daily mean temperature or temperature sum instead of a given day and night temperature is a possibility of saving energy, as also is the maintaining of a diurnal period of up till 6 hours with a higher night than day temperature beginning at sunset when the thermal screens are closed.<p>Soil heating until 20 °C did not influence production and quality,whilst a 12% reduction in light had a negative effect on both.<p><TT></TT&gt