THE INFLUENCE OF SEASON ON CUT FLOWER CONDITIONING RESPONSE IN 'WHITE SIM' CARNATIONS

Transcription

1 THE INFLUENCE OF SEASON ON CUT FLOWER CONDITIONING RESPONSE IN 'WHITE SIM' CARNATIONS Jack L. Paul, Anton M. Kofranek and John Kubota Department of Environmental Horticulture University of California Davis, California, U.S.A. Abstract Longevity (vase life) of 'White Sim 1 carnation cut flowers was measured monthly for one year. Five conditioning treatments were compared: control (water only); 10 minute stem emersion in 1000 ppm AgN0 3 ; Ag emersion plus 10 or 25% sugar for 24 hrs; and 25 ppm AgN03 plus 4% sugar continuously. Longevity in days of the control and continuous Ag plus sugar were 6-7 and days, respectively. Neither treatment showed a distinct seasonal trend. The Ag emersion only increased longevity by 3 days over the control throughout the year. Ag emersion plus 25% sugar for 24 hours increased longevity over the Ag emersion by only 3 days during fall and winter but only 1.5 days during spring and summer. The 10% sugar treatment for 24 hrs did not give a consistent increase over Ag emersion only. Introduction Conditioning carnation cut flowers with preservative solutions containing sugar or with a bactericide has been shown to enhance vase life (1, 2). The object in conditioning cut flowers with a sugar solution is to increase the carbohydrate reserve of the flower while the bactericide is thought to prevent bacterial plugging of water conducting elements. Experiments on conditioning do not consistently produce a beneficial increase on keeping life. Factors such as length of time in the conditioning solution, sugar concentrations, quality of the flowers and the season of harvest may result in an inconsistent response. Of these, season may have a particularly important influence since there is reason to expect a varied response due to season. For southern California conditions Kohl and Nelson (3) measured carnation vase life over a 10 month period and found that maximum longevity occurred in February and minimum longevity occurred in September. They concluded that light was not the cause of variation in vase life, but they did find an inverse relation between longevity and 'average' greenhouse temperature. Lancaster (4) studied keeping life of carnations for Colorado conditions and during the low light months of winter; he found a direct relation between vase life and amount of sunlight. Both observations show that the preharvest environment was related to keeping quality. Furthermore, both observations suggest that carbohydrate status is directly associated with keeping life. Plants grown under adequate light and low greenhouse temperatures should have higher carbohydrate reserves than plants grown under low light or high temperature. Thus, plants having high carbohydrate reserves might respond less to conditioning in sugar than would plants having low carbohydrate reserves. If carbohydrate reserves varies with season, then response to conditioning should vary also. Acta Horticulturae 71,

2 Experimental Methods To examine the influence of season on vase life response to conditioning, an experiment was performed from September 1973 through August White Sim carnations were obtained each month from a grower in south San Francisco. The flowers were of highest quality and very well grown. The flowers were picked up from the grower on the same day they were cut. They were packed in ice but not placed in water and returned to Davis where they were immediately graded and stems were recut to 55 cm. The flowers were treated immediately after grading as follows: Treatments Keeping solutions_for longevity study 1. Control (no conditioning) Deionized water (DI) 2. Continuous 4% sugar solution + 25 ppm AgNO^ DI water containing 4% sucrose + 25 ppm silver nitrate (AgNC^ ) 3. Silver dip (stems dipped in 1000 ppm AgNO} for 10 minutes then placed in DI after stems dried) Deionized water (DI) 4. 10% sugar pulse (stems dipped in 1000 ppm AgNC^ for 10 minutes, then into 10% sucrose solution for 24 hours) Deionized water (DI) 5. 25% sugar pulse (stems dipped in 1000 ppm AgNO^ for 10 minutes, then into 25% sucrose solution for 24 hours) Deionized water (DI) Flowers for treatments 1, 2 and 3 were placed in the keeping solution on the same day they were collected and for treatments 4 and 5, 24 hours later. Keeping life for all treatments was measured from the day of cutting. Inspection of the flowers was done daily. When flowers showed the first signs of wilting, they were removed and keeping life, in days, was recorded. Each treatment consisted of six flowers, each placed in individual containers with 100 ml of keeping solution. All experiments were performed in a laboratory at 23 ± 1 C with continuous fluorescent light (1100 lux). Results are presented as means of six replicates for each treatment. Results and Discussion Mean longevity in days for each treatment is plotted monthly (figure 1). Flowers in the control treatment had the shortest vase life. This was expected since in the absence of bactericide, stem plugging is likely The vase life was 7-8 days for most months which is unusually >ong for a control treatment. The reason for this is in part because the flowers were of superior quality. The continuous sugarsilver treatment (No. 2) gave maximum longevity on all occassions. This treatment indicates the maximum longevity when bacterial growth 274

3 is eliminated and sugar is not limiting. It is not necessarily the maximum longevity since there may be other limiting factors not considered here. Comparing treatments 1 and 2 shows the increase that might be realized if the consumer used a preservative. The three conditioning treatments lie between the control and continuous sugar-silver treatment. The "silver dip" (No. 3), which just eliminates microorganism growth, showed significantly greater longevity than the control (No. 1) on all occasions except in October. The average increase in longevity above the control was 3.1 days. We assume that carbohydrate was limiting in this treatment. Flowers conditioned for 24 hours in 25% sugar (No. 5) had consistently longer vase life than the "silver dip" alone (No. 3) on all occasions except July. Conditioning flowers in 10% sugar (No. 4) was less effective than in 25% sugar. This treatment was inconsistent but was significantly better than the "silver dip" on just four occasions. The reason for the erratic behavior and the overall low increase in this treatment is not clear. There appears to be distinct seasonal trends in each treatment. No attempt was made to relate preharvest environment (light and temperature) to vase life of the treatments although it undoubtedly plays a significant role. The continuous sugar treatment and the 25% sugar treatment showed two peaks in vase life: one in January and in July. The control and silver dip treatments had a maximum vase life in July. The question posed in the introduction regarding the effectiveness of conditioning throughout the year will now be considered. The increase in vase life by silver conditioning over the control, except for the month of October, remains relatively constant throughout the year. While the keeping life varies with season, the increase over the control appears to be the same for most months. A different picture is given with sugar conditioning. The benefit derived from sugar is the increase over the "silver dip" treatment alone. This increase is not constant throughout the year but is greater during the fall and winter months than in the spring or summer. Thus, vase life increase due to sugar conditioning appears to be affected by season; however, conditioning with a germicide appears to be independent of season. The following table summarizes the increase due to conditioning during fall-winter and spring-summer: Conditioning treatment Sept-Feb Mar-Aug Ag dip: Average increase over control (days) 10% sugar: Average increase over Ag dip (days) 25% sugar: Average increase over Ag dip (days) These data indicate that it is beneficial to condition carnations with a germicide, but it may be questionable to condition them in a 10% sugar solution. The 25% sugar conditioning, appears most beneficial during fall and winter but not in spring and summer. The results bear 275

4 out the contention that conditioning flowers to enhance carbohydrate status is dependent on season, but it should be pointed out that response to conditioning may depend on cultivar and cultural conditions. References Farnham, D. S., Barr, Charles and A. H. Halevy The value of using chemical solutions for conditioning and bud opening carnations. Florists' Review, 148:27-28, Kofranek, A. M. and J. L. Paul The value of impregnating cut stems with high concentrations of silver nitrate. Acta Horticul turae. 41_: Kohl, H. C. Jr., and R. L. Nelson Answers to some questions about carnation vase life. The Bloomin' News. pp July. Lancaster, D. M Effects of preharvest environment on keeping life of cut carnations. Colo. F1. Gr. Assoc. Inc. Bull Acknowledgements The authors wish to thank Mr. Peter Mazzanti of South San Francisco for supplying the flowers each month during this study and to the Fred C. Gloeckner Foundation for partial funding during the latter portion of this experiment. 276

5 S 0 I N L I D J I I I F M A I I M J 1 J 1 A MONTH Figure 1 - Monthly variation of carnation longevity for treatments: various 1. Control 2. Continuous sugar and silver nitrate 3. Si 1ver dip only 4. Silver dip + 10% sugar pulse 5. Silver dip + 25% sugar pulse Shaded data points are not significantly different at 5% level. Statistical comparisons can only be made vertically (monthly). 277