Growth Inhibitor Accumulates in the Nutrient Solution of Closed System Rose Cultivation

Growth Inhibitor Accumulates in the Nutrient Solution of Closed System Rose Cultivation N. Sato Shizuoka Agricultural Experiment Station Japan Keywords: rose, soilless culture, rock wool, closed system, autotoxicity Abstract The circulating solution was collected and analyzed for its nutrient concentration. Three types of solutions were prepared for the bioassay. One was the circulating nutrients solution. Activated charcoal was added to second solution. The third solution was prepared to the analyzed formula of nutrients solution using distilled water. The rooted cuttings of rose were planted in each solution and incubated in the growth chamber. The rate of change of fresh weight before and after the incubation was biggest for the prepared solution, which does not include the circulating solution. The fresh weight growth rate was smallest for the circulating solution, and the results for the activated charcoal treatment was between them. Since the activated charcoal does not have a sterilization effect, it is possible that the growth inhibitors accumulated in the solution during the circulating cultivation of roses. INTRODUCTION The total area of cut rose production cultivating by rock wool in Japan was 267 ha in 1998, which is almost half area of the total rose production in Japan (Horiuchi 2000). Most of the hydroponic production of cut roses is accomplished in an open system, as it is difficult to maintain the stable production of cut roses in a closed system (Horiuchi 2000). Closed hydroponics offer options to reduce the polluting effects from greenhouses (Van Os 1991). However, Yu et al. (1993) indicated that the exudates from the plants to the nutrient solution might decrease the plant production, and this inhibition has been attributed to the autotoxicity from the root exudates. Asao et al. (1998) reported the fruit yield of cucumber plants decreased significantly in the late reproductive stage and the growth was recovered by the biweekly renewal of nutrients or supplementation of activated charcoal to the nutrient solution. Asao et al. (2002) also reported there are many autotoxic substances in many kinds of flowers. It is possible that root exudates might decrease the rose growth rate in a closed hydroponic system. We investigated the possibilities of the accumulation of the growth inhibitor in the circulating solution. MATERIALS AND METHODS To make the long term circulating nutrient solution, we cultivated the Rosa hybrida L. cv. Asami Red (Rote Rose) by the rock wool closed system, without change the circulating solution. Well-rooted single node cuttings of Rote Rose growing on rock wool blocks (10cm x 10cm x 10cm) were planted in the foamed polystyrene bed containing rock wool slabs (10.5cm x 22.5cm x 91cm). Six rock wool blocks were placed in a slab. Two beds were placed side by side on the greenhouse benches (0.7m x 7.4m x 0.5m), which were spaced at 1.6m on-center (Fig.1). The roses were managed by an arching cultivation technique (Ohkawa,K. and Suematsu, M. 1999). The total harvested cut flower numbers and chlorosis cut flowers numbers were recorded from September 1 st, 2003 to June 30 th, 2004. The experiment performed with 4 replications. Each block consisted 12 plants. The solution, which has an electrical conductivity (EC) of 0.7dS/m (Table 1), was drip-irrigated hourly from 6am to 15pm. The drainage was collected in a tank, and reused as a nutrient solution. When the nutrient solution was less than a certain level in the tank, the newly adjusted solution (Table 1) was filled into the tank. The volume of the nutrient solution tank was 65L for 192 plants or 0.3L/plant. The treatment began in August 17 th, 2003. The circulating solution was collected and analyzed for the nutrient concentration (NO 3 -, H 2 PO 4 -, K +, Ca 2+, Mg 2+, Cl -, and SO 4 - by atomic absorption spectrometer (SHIMAZU CORPORATION AA-6650) and ion meter (Dionex Corporation DX-120). Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005 511

Three types of solutions were prepared for the bioassay (Fig. 2). One was the circulating nutrients solution, which was diluted by an equal volume of distilled water. Activated charcoal was used in the second solution for 24 hours to remove the organic substances, and this solution was also diluted by an equal amount of distilled water. Asao et al. (1998) used activated charcoal (4 g/l) to remove the root exudates in the nutrient solution of cucumber hydroponics. The activated charcoal we used (33g/L) was enough to remove the root exudates. The third solution was prepared to the specifications of an analyzed formula of nutrients solution in distilled water (Table 2). Micronutrients were added to each solution before the bioassay began because activated charcoal also absorbs the EDTA-Fe (Yu et al. 1993). The single nodes of cut roses were planted in a container containing 20L of nutrient solution (Table 1) on March 10 th, 2004. Eight rooted cuttings of rose were planted in one container (20cm x 25cm x 5cm), which contained 2L of each solution (Fig. 3, Table 2), and incubated in the growth chamber from May 11 th to 27 th. The temperature of the light period was 28 degrees centigrade and the dark period was 23 degrees centigrade. The light intensity was 18,000 lux. The fresh weights of the rose nodes were measured before and after the incubation. The chlorophyll meter value of every three leaves of the cuttings were measured with a SPAD-502 Chlorophyll Meter (KONICA MINOLTA HOLDINGS, INC.). The Chlorophyll meter values correlated with the chlorophyll contents of the leaves (Kariya et al., 1981). RESULTS During the cultivation in the closed system, the analysis shows that high level of Magnesium and EC were detected (Table 3). After 5 months of rose cultivation in a closed system, the rate of chlorosis in the rose shoot was over 40%. And the rate of chlorosis shoot in the shoot reached over 70% in May. No chlorosis in the shoot was found in the open system (Fig. 4). The yield and quality of cut flowers cultivated in the closed system was lower, compared to those cultivated in the open system after 5 months of treatment (Table 4). The yield of roses from the closed system was much lower than open system after April, 8 months after the treatment began (Fig. 4). In the bioassay test, the change in fresh weight before and after the incubation was greatest when the prepared solution used, this solution did not include the circulating solution (Table 4). The fresh weight growth rate of the roses was smallest when using the circulating solution, and the activated charcoal treatment results were between them. The chlorophyll meter value of the leaves showed similar results to the growth rate, the leaves grown in the prepared solution using the distilled water showed the highest value (Table 4). The chlorosis was investigated in the circulating solution and the activated charcoal treatment. But the symptom was slightly lighter in the activated charcoal treatment (Fig. 5). The roots were almost rotting in the circulating solution. The roots of the activated charcoal treatment were not rotten, but browned. DISCUSSION In closed hydroponic culture without renewal of the nutrient solution, fruit yield of cucumber plants decreased significantly in the late reproductive stage (Asao et al., 1998). Asao et. al. detected a number of growth inhibitors by the cucumber root exudates from the closed hydoroponic nutrient solution(asao et al., 1999). They also found that the 2,4,- dichlorobenzoic acid was the strongest inhibitor in cucumber. In the experiment using roses, the chlorosis of cut flower leaves occurred after 4 months in the closed hydoroponic treatment. The rose production cultivated in closed system decreased significantly after 8 months. The EC and Magnesium in the nutrient solution of the closed system is higher than the open system, but the value of EC2.0dS/m is at a normal level for rose hydro culture (Kajihara et al., 2005). In the bioassay test, the growth rate was biggest in the prepared solution, which does not include the circulating solution. The fresh growth rate was smallest for the circulating solution, and the activated charcoal treatment was between them. Since the activated charcoal does not have the sterilization effect, pathogenic organism might not suppress the growth. If there exists an autotoxic subustance in roses like cucumbers, the concentration of 512

the autotoxic substances in nutrient solution may be high, since we used a small volume of tank (0.3L/plant). Asao et al. (2002) also reported, there are many autotoxic substances in many kinds of flowers. It is possible there are autotoxic substances exudated by roses. Literature Cited Asao et al. 1998. Decrease of yield of cucumber by non-renewal of the nutrient hydroponic solution and reversal by supplementation of activated charcoal. J.Jpn.Soc.Hort.Sci67,99-105(in Japanese with English summary). Asao et al. 1999. Influences of phenolics isolated from the nutrient solution nourishing growing cucumber (Cucumis sativus L.) plants on fruit yield. J.Jpn.Soc.Hort.Sci: 68,847-853(in Japanese with English summary). Asao et al. 2002. Effects of non-renewal of the nutrient solution and addition of activated charcoal on the growth of flowers in hydroponics. J.Jpn.Soc.Hort.Sci: (extra)70-1,325 (in Japanese). Asao et al. 2004. Mitigation of cucumber autotoxicity in hydroponic culture using microbial strain. Scientia Horticulturae: 99 207-214. Horiuchi,M. 2000. Problems of rose production in Japan on management bases. Agriculture and Horticulture: 75(7)773-777(in Japanese). Kariya et al. 1981. Estimation of the chlorophyll contents in rice leafs using by the green meter. Japan.J.Crop.Sci. 50: (1) 21-22(in Japanese). Ohkawa,K. and Suematsu, M. 1999. Arching Cultivation Techniques for Growing Cut-roses. Acta Hort 482:47-52. Van Os, E.A., Ruijs, M.N.A. and van Weel, P.A. 1991. Closed business systems for less polution from greenhouses. Acta Hort 294:49-58. Hort.Sci., 69, 423-427 (2000). Yu, J.Q., Lee, K.S. and Matsui, Y. 1993. Effects of the addition of activated charcoal to the nutrient solution on the growth of tomato grown in the hydroponic culture. Soil. Sci. Plant Nutr. 39, 13-22. 513

Tables Table 1. Nutrient solutions 1 used for closed hydroponic system of roses. y Chemicals Amounts (mmol/l) 1 Ca(NO 3 ) 2 4H 2 0 6.00 KNO 3 1.50 MgSO 4 7H 2 0 2.00 NH 4 H 2 P0 4 5.40 H 3 BO 3 2.69 10-2 ZnSO 4 7H 2 0 1.51 10-3 MnSO 4 5H 2 0 9.11 10-3 CuSO 4 5H 2 0 6.28 10-4 NaMoO 4 2H 2 0 1.69 10-4 NaFe-EDTA 0.05 1 Full strength. 2 Amounts of salts per 1L of water. Table 2. Nutrient solutions used for bioassay. y ph EC NO 3 -N P Ca Mg K Cl SO 4 ds/m mmol/l mmol/l mmol/l mmol/l mmol/l mmol/l mmol/l Circulating solution Circulating solution 7.7 1.47 6.3 2.1 5.4 8.4 4.6 2.7 5.4 supplemented by activated 7.4 1.15 5.0 2.7 4.2 7.0 3.7 2.6 5.3 charcoal Prepared from distilled water 6.8 0.88 6.2 3.0 2.8 7.0 3.8 0.1 0.5 Table 3. Nutrient solution during the cultivation period. g p date ph EC NO 3 -N P Ca Mg K Fe ds/m mmol/l mmol/l mmol/l mmol/l mmol/l ppm 2003 Aug. 7.0 1.56 11.4 10.2 13.8 11.0 4.2 2.1 2004 Jan. 6.0 1.94 6.8 8.3 15.9 17.6 2.7 1.0 Closed system 2004 Apr. 7.0 2.69 12.3 4.0 10.8 16.5 8.6 2.4 2004 Jul. 6.8 2.09 8.8 10.7 7.5 15.2 5.4 2.1 2003 Aug. 6.8 1.46 6.6 8.2 10.1 4.1 2.2 1.9 Open system 2004 Jan. 6.5 1.67 9.3 5.3 9.0 6.8 3.3 2.1 2004 Apr. 6.8 1.83 8.3 12.7 7.1 6.2 4.4 2.1 2004 Jul. 0.0 1.32 10.0 9.4 12.5 6.5 3.7 1.4 514

Table 4. Rose production and quality in a closed and an open system of hydroponics. Table 4 Rose production and quality in a closed and an open system of hydroponics Harvest period September,2003 to January,2004 February to Jun,2004 hydoroponic system No. of shoots Shoot length Fresh weight Cumulative shoot fresh weight (No./plant) (cm) (g) (g/plant) closed system 7.4 76.8 40.2 288.0 open system 7.6 77.4 42.2 297.9 t-test 1 NS NS NS NS closed system 7.1 82.3 55.5 371.2 open system 10.1 87.0 61.6 587.4 t-test * * NS * Data were taken from September 1, 2003 to June 30, 2004 1 NS,* Insignificant at P-0.05,significant at P=0.05, respectively. Table 5. Effect of activated charcoals treatment of the circulating solution to the rooted cut rose growth during 16 days 1. g g y Total weight (g) Chlorophyll meter value before (a) aftere (b) rate (b/a) % after treatment 2 Circulating solution 9.8 9.5 97 b 30.3 b Circulating solution supplemented by activated charcoal 9.6 10.9 113 a 35.1 ab Prepared from distilled water 9.4 11.3 119 a 42.4 a NS 3 NS 1 Different letters within a column indicate significance at the 5% level by the Tukey test 2 SPAD-Chlorophyll value (KONICA MINOLTA HOLDINGS, INC.) 3 Not significant by the Tukey test. Figures Sampling Analyze the nutrition Activated Chacoal 33g/L 24h Nutrient elements were added to the distilled wate The solution was diluted by the same volume of distilld water,and added the micronutrients, then used for the bioassay Fig. 1. The cross section of arching technique. Fig. 2. Test procedure. 515

Fig. 3 Bioassay in growth chamber. Number of cut flowers 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Closed system chlorosis Sampling Open system chlorosis Sep Oct Nov Dec Jan Feb Mar Apr May Jun Fig. 4. Yield and chlorosis rate of rose shoots cultivated by closed system and open system. 90 80 70 60 50 40 30 20 10 0 Chlorosis shoots % Fig. 5. Rose cuttings after 16 days of treatment. 516