INFLUENCE OF ELECTRICAL CONDUCTIVITY, RELATIVE HUMIDITY AND SEASONAL VARIATIONS ON THE BEHAVIOUR OF CUT ROSES PRODUCED IN SOILLESS CULTURE I. Urban*, R. Brun** and L. Urban** *C.N.I.H. Station d'expérimentation de Nice-La Gaude BP 31-06201 Nice cedex 3 - France **Unité de recherche intégrée en horticulture Institut National de la Recherche Agronomique Route des colles - Sophia-Antipolis 06410 Biot-France Index words: postharvest, water balance. Abstract Cultural factors of plant production should not affect in a negative way post-production quality. With this aim in view, we observed the behaviour of cut 'Sonia' roses placed in a climatic room (20 C, 60% RH, 1200 lux 12h/24). Flowers were collected throughout the entire production season from plants grown in rockwool slabs at two levels of electrical conductivity of the nutrient solution (1.8 and 3.8 ms/cm) in two greenhouses: one control and one with high pressure mist (relative humitity > 70%). The post-harvest criteria considered were the following: the intensity and evolution of the opening of the flowers with reference to different phenological stages, water uptake and transpiration, and the evolution of the weight of the flowers during their vase-life. Relative humidity levels and electrical conductivity of the nutrient solution did not affect the opening of the cut flowers and their vase-life. These results indicate that cultural factors have less importance than post-havest factors on the behaviour of cut roses. However, it should be noticed that there was a strong seasonal influence on transpiration and water uptake. There was an increase in transpiration and water uptake from summer to autumn followed by a decrease until spring. These observations are related to measurement of stomata closure threshold performed during the growing period. 1. Introduction Numerous studies have been conducted on the effects of postharvest conditions and treatments on the vase behaviour of cut flowers. Numerous studies have also been conducted on the methods used to improve cultural techniques. The criteria used to judge these techniques are often productivity improvement, visual quality improvement, reduction of production costs, or their influence on the environment. However, few studies have related the effects of production techniques on the vase behaviour of cut flowers. And it is necessary to know if the techniques recommended for their positive effects on production do not have negative impact on flower behaviour once these flowers reach the commercial circuit. For example, Slootweg and Van Meeteren (1991) have shown that greenhouse lighting of roses led to a poor regulation of transpiration and therefore caused brittleness of the flowers. Studies have been conducted on gladiolus (Anserwadekar and Patil, 1986) and Anthurium (Paull et al., 1992). Halevy and Mayak (1979) reported that high conductivity had negative effects on the shelf-life on chrysanthemums. But they emphasized that these effects seemed to be more related to water stress. It seems accepted that high salinity levels reduce vase-life of flowers (Nowak and Rudnicki, 1990; Kreij and Van den Berg, 1989). Acta Horticulturae 408, 1995 Soilless Cultivation Technology for Protected Crops 101
The experimental device developed by the URIH station in Sophia-Antipolis helps to determine the effects of the electrical conductivity (Ec) of the nutrient solution and of high pressure mist on the production of 'Sonia' roses grown in rockwool. It seemed worth evaluating the effects of these techniques on the vase behaviour of these flowers at different seasons. 2. Materials and methods 2.1. Cultural techniques Rose plants (Rosa hybrida cv 'Sonia') were grown in rockwool slabs and placed at a density of 5.6 plants/m2 in two identical glass greenhouses. The irrigation frequencies were the same for all treatments and depended on transpiration. Leaching was at least 30% of supplied volume. 2.1.1. Climate control Temperature and relative humidity (RH) were monitored by computers. The setpoint temperature that determines the opening of the windows was kept at 22 C. Minimum temperature was kept at 17 C. In one of the greenhouses, RH was kept at 708 with a high pressure mist system (The Fog System) that delivered droplets of a diameter inferior to 10 (tm. In the other greenhouse, the screening pad was automatically pulled when exterior global radiation reached 800 W/m2 and temperature rose above 30 C. 2.1.2. Fertirrigation The nutrient solution was that recommanded by Brun and Tramier (1988). The composition of the solution was monitored by computer. The composition of the solution for an Ec = 1 650 ^S.cm" 1, at 25 C was as follows (in mmol/1) : N03 : 8,4 ; H2P04 : 1,7 ; S04 : 1,5 ; CI : 1,1 ; NH4+ : 0,7 ; K+ : 5,0 ; Ca++ : 3,0 ; Mg++ : 1,2 ; Na+ : 0,8 et, en im : Fe+++ : 23 : Mn++ : 9 ; Zn++ : 3,5 ; B : 24 ; Cu++ : 9,5 ; Mo : 0,3. To obtain the desired Ec (1.8 and 3.8 ms/cm) in the leaching solution, the concentration of the macro elements changed proportionally, whereas the concentration of the micro elements remained unchanged. 2.2 Harvest Vase behaviour tests were performed 8 times between April 1991 and May 1992. The goal of this study was to observe the vase behaviour of the flowers as a fonction of Ec (1.8 and 3.8 ms/cm) and relative humidity control (high pressure mist vs control). The flowers were harvested at normal commercial stages of development, brought in refrigerated trucks to the laboratory and placed in a climatic room (20 C, 60% RH, 1200 lux 12h/24). 2.3.Study of vase behaviour In the climatic room, the flowers were placed in 500 ml test-tubes, one flower per test-tube, and filled with tape water. The following observations were made: -on the opening of the flower buds with reference to the different morphological stages 102
described by Paulin (1973), -on the vase life of the flowers, -on water uptake and transpiration by weight measurements, -on the weight evolution of the flower stem. At each harvest, 20 flowers were chosen for each treatment. Data were analysed by ANOVA. 3. Results and discussion 3 1 Opening and vase behaviour All flowers reached full bloom except those harvested on 11 November 1991. Ec and greenhouse relative humidity control had no significant effect. Vase life data are shown in Figs. 1 and 2. The high pressure mist system only worked during the warm periods. As for flower opening, no significant difference was observed among treatments for flowers harvested on the same day. RH during the growing period did not seem to affect the vase behaviour of the flowers. De Kreij and Van Den Berg (1989) reported differences in vase behaviour of flowers grown at high Ec levels (5 to 8 ms/cm) These values are very high and are not found in normal cultural practices. In our study, we did not try to evaluate the effect of very high Ec. Our aim was to know if the postharvest behaviour was a factor to consider when cultural choices are made. According to our results, we can conclude that the grower's decision must be made as a fonction of production results: the effects of Ec and RH during the growing period are limited if the values are not too high. 3.2. Water uptake and transpiration measurements 3.2.1. Air relative humidity For tests made in April and in June 1991, transpiration of flowers grown in high RH levels was either equal than that of flowers grown in low RH levels. This may be due to the fact that leaves of rose plants grown in high RH levels have a lower epicuticular wax load and, as a result, a higher cuticular transpiration rate (Urban et al., 1993). The water uptake pattern was the same than the transpiration one (fig.3). The ratio water uptake/transpiration was higher for flowers grown without relative humidity control (Fig.4). These observations were not confirmed by the two tests done in July 1991. 3.2.2. The nutrient solution electrical conductivity On all the flowers tested, water uptake and tranpiration were higher for flowers irrigated with a solution of 1.8 ms/cm (Fig.5). On the other hand, during the vase-life period, the ratio water uptake/transpiration was, at the beginning, higher for flowers grown with a high Ec solution but then, this seemed to deteriorate more rapidly. 3.3. Evolution of flower stem weight When a significant difference in behaviour was observed among treatments, fresh weight gain was more important for flowers grown with an Ec solution of 3.8 ms/cm (Fig.6). Generally, this difference persisted during the entire vaselife period. 3.4. Seasonal effect Figure 7 shows that seasons affected transpiration. Transpiration of flower stems was 103
higher when the outside temperature was lower. This was due to cultural factors since all post-harvest measurements were made in a controlled environment. Urban et al.( 1993) observed a 1 MPa increase in the threshold value of water potential at stomatal closure from spring until the beginning of fall. This increase was followed by a decrease. These seasonal variations of the stomata closure threshold may give an explanation to the seasonal variations in transpiration rates of cut roses. Our findings come close to those reported by Slootweg and Van Meeteren (1991) when the vase behaviour of roses grown with artificial lighting was compared to that of roses grown without it. The same authors also noticed levels of transpiration that were related to growing conditions. 4. Conclusion In our experiments, control of the RH by high pressure mist and monitoring of the electrical conductivity of the nutrient solution did not affect the vase behaviour of 'Sonia' roses. This confirms the fact that post-harvest conditions have a greater impact on vase behaviour of flowers than cultural conditions. However, during our trial, the flowers were not stressed. It is possible that the water variations due to air RH and Ec affect vase behaviour when distribution conditions are less favorable. In these cases, post-harvest quality preservation techniques should bring satisfactory answers. This study showed that season affected flower stems water uptake and transpiration and that the plant behaviour after harvest was the same as that of the growing period. Further research is needed to correlate these observation on transpiration to vase life behaviour. Then, perhaps, we could begin to explain the growers' observations regarding the cut flower behaviour problems they encounter at some periods of the year. References ANSERWADEKAR K.W. and PATIL V.K. - 1986. Vase life studies of Gladiolus (Gladiolus grandiflora) cv H.B. PITT. i. Effect of NPK and Spacing on vase life, ii- Effect of differentchemi cals. Acta Horticulturae 181: 279-283. BRUN R. and TRAMIER P.H. - 1988. Culture du rosier sur laine de roche. PHM Revue Horticole. n 289, août-septembre 1988, pp. 43-51. DE KREIJ C., VAN DEN BERG Th. - 1989. Lage Ec beinvloedt kwaliteit roos positief. Vakblad voor de Bloemisterij, 27/01/1989 (4), pp. 154-155. HALEVY A. and MAYAK S. - 1979. Senescence and post-harvest physiology of cut flowers, part 1. Horticultural Reviews 1: 204-236. NOWAK J. and RUDNICKI R. - 1990. Post harvest handling and storage of cut flowers, florist greens and potted plants. Timber Press. Portland. Oregon - U.S.A. - p. 32. PAULIN A. - 1973. Conditions de réalisation d'essais de survie de fleurs coupées. L'Horticulture Française, 35: 3-9. PAULL R.E., HIGAKI T. and IMAMURA J. - 1992. Season and fertilisation affect the post-harvest flower life of anthurium, Scientia Hortic. 49 : 125-134. SLOOTWEG G. and VAN MEETEREN V.- 1991. Transpiration and stomatal conductance of roses, cv Sonia, grown with supplemental lighting. Acta Horticulturae 298: 119-125. URBAN L PYRRHA P. AND PEREZ G. - 1993. Variations saisonnières de la transpiration de feuilles excisées de Rosa hybrida cv Sonia. Agronomie (submitted). 104
Ec = 1.8 S Ec =3.8 Figure 1: Vase life of 'Sonia' roses as a function of harvest date and electrical conductivity of the nutrient solution- Fog S Non Fog Figure 2: Vase life of 'Sonia' roses as a fonction of harvest date and presence or absence of relative humidity control. 105
Figure 3: Water uptake and transpiration of 'Sonia' roses as a function of the presence or absence of relative humidity control. Figure 4: Evolution of the ratio water uptake/transpiration as a function of the nutrient solution electrical conductivity and the presence or absence of relative humidity control. 1 2 3 4 5 Time (days) 6 7 ù Trap Ec3.8 Figure 5: Water uptake and transpiration of function of the nutrient solution electrical 'Sonia' roses as a conductivity. 106
Time (days) Ec= 1.8 4 Ec= 3.8 Figure 6: Evolution of the fresh weight of the flower stems as a function of the nutrient solution electrical conductivity. Harvest date Figure 7: Transpiration of 'Sonia' roses during the first hours of their vase life period as a function of harvest date. 107