00 Growth_and_Early_Yield_of_Stenting-Propagated_Domestic_Roses_Are_Not_Affected_by_Cytokinins_Applied_at_Transplanting.pdf1.12MB

• Introduction
• Materials and Methods
• Plant materials
• Stenting and treatments
• Experimental conditions
• Growth measurements and design
• Statistical analysis
• Results and Discussion

Introduction

 Stenting was developed for quick propagation of roses under conditions prevailing in the Netherlands, based on cutting and grafting being performed in one action. In Dutch the word ‘stenting’ means ‘to stem’ (van de Pol and Breukelaar, 1982), and it’s a combination of  ‘stekken’ meaning ‘to strike a cutting’ and ‘enten’ meaning ‘to graft’. The success of simultaneous cutting and grafting is cost effective. A piece of stem of a cultivar with one leaf and a dormant bud is grafted on a single internode of the rootstock. Formation of the graft union and adventitious roots occur simultaneously, resulting in a complete plant in three weeks. This plant has advantages like higher yield and quality, and resistance to the crown gall disease (Park and Jeong, 2010). During six years of experiments, Wagenknecht and Radke (1987) found only minor differences in bloom yield of cutting-propagated rose plants as compared with grafted ones. The cutting-propagated plants tended to be superior in the first three years, whereas the grafted plants were somewhat better in the last three years. Moreover, since stenting can be performed all year, stenting provides the possibility of year-round propagation. Despite these advantages of stenting propagation for cut roses, there have been a few studies on this method and it is not widely used due to difficulty and inefficiency of this important propagation method. For development of an efficient propagation method we need to establish a storage system of preventing root senescence of stenting propagated roses which requires high quality and yield.

 Recovery and maintenance of photosynthetic activity along with rapid root growth of stentingpropagated roses after transplanting is important for survival and successful establishment. Root damage caused by uprooting and transplanting can reduce the effective root area and limit the ability of plants to absorb water and nutrients (Kramer, 1983). Transplant shock can cause water stress (Berkowitz and Rabin, 1988) and decrease the nutrient uptake of plants (Bloom and Sukrapanna, 1990). Initiation of new roots and rapid elongation of existing roots into the surrounding soil may help plants to recover more quickly form the harmful effects of transplant shock.

 Plant growth regulators (PGRs) are organic substances that influence physiological processes of plants at extremely low concentrations (Zahir et al., 2001). These are either natural or synthetic compounds that are applied directly to a target plant to alter its life processes or its structure to improve quality, increase yield, or facilitate harvesting (Nickell, 1982). There are five major classes of PGRs including auxins, gibberellins, cytokinins, abscisic acid and ethylene. Cytokinins are a class of plant hormones that influences many developmental processes including leaf senescence, apical dominance, chloroplast development, anthocyanin production and regulation of cell division (Rani Debi et al., 2005). Cytokinin, together with auxin plays an essential role in plant morphogenesis, having a profound influence on the formation of roots and shoots and their relative growth. Clarke et al. (1994) proposed that cytokinin may inhibit the catalytic effects of ethylene on senescence at the level of its perception, as exogenous cytokinin had a stronger effect on the delay of senescence than did treatment with silver ions. The two plant hormones ethylene and cytokinin are known to act antagonistically on harvest-induced senescence in broccoli: ethylene by accelerating the process and cytokinin by delaying it (Gapper et al., 2005).

 The significance of plant growth regulators for cut roses propagated by stenting has hardly been investigated, although their application in cut roses has been successful. Moreover, there have been only few studies reported comparing yield of cut roses. This study was carried out to investigate uses of preventing root senescence of and to evaluate the effect of cytokinins on the growth and yield of stenting-propagated domestic cut roses.

Materials and Methods

Plant materials

 Plant materials, grown in a commercial rose farm (Dowon Rose Farm, Gimhae, Korea), consist of flowering stems with full-grown leaves and just opening flowers. After normal harvesting, each individual stem was kept apart and cut into sections with a five-leaflet leaf and a dormant bud. First grade flowering shoots were harvested at the stage when two sepals were free from the flower bud (Jensen and Hansen, 1971). Two domestic spray rose ‘New Man’ and ‘New Lady’ used in this study. Rosa indica ‘Major’ was grown as a rootstock material in a commercial greenhouse (Borame Rose Farm, Gimhae, Korea). The softwood material as a scion was harvested at a stage when leaves were well developed and thorns could be broken off easily (van de Pol et al., 1986).

Stenting and treatments

 As a rootstock, a piece of a single internode without a bud was used. The rootstock cuttings were removed of all leaves and buds. Top of the rootstock internodes and the basal part of the scions were cut at an angle of 45^ο for grafting. For a good development of the graft, partners were in close contact. Scion-rootstock unions were stuck in rockwool cubes (5 cm×5 cm×5 cm, Delta, Grodan, Denmark) and were placed in a graft-take chamber for five days before being placed on misted greenhouse bench in Boramae Rose Farm, Gimhae, Korea. A 10 mg·L^-1 kinetin or 50 mg·L^-1 BA solution either as a foliar-spray or drench was exogenously applied on Jul. 29, 2009. Grafted plants were transplanted to rockwool slabs (10 cm×15 cm×100 cm, UR, Korea) on two different dates, either 0 (Jul. 29, 2009) or 7 days after application (Aug. 5, 2009) of either one of the cytokinin solutions. At 47 days after transplanting all shoots were bent (arched) to promote production of vigorous new basal shoots. For prevention of powdery mildew and aphids, chemicals were sprayed weekly. Plant growth and flower quality were investigated for three successive harvests during the period of six months (from October 2009 to March 2010).

Experimental conditions

 A nutrient solution was supplied daily through an arrow dripper (Golden Drip 8, Shinhan Farm Industry, Masan, Korea) at 7:00, 9:00, 11:00, 13:00, 15:00, 17:00, and 19:00 O’clock for three minutes each time. About 595 mL solution per plant was supplied daily, and a constant nutrient and water status in the root zone were maintained. The composition of the nutrient solution was based on the formulation by the Aichi-ken Hort. Expt. Station, Japan. The pH and electrical conductivity (EC) of the nutrient solution supplied were 5.8 and 1.2 mS·cm^-1, respectively. Mean daily air temperature and relative humidity (RH) measured during the experimental period by a digital thermometer (Thermo Recorder TR-72U, T&D Corp., Japan) were 25.1 and 70.3% in the greenhouse.

Growth measurements and design

 The early stage growth parameters measured were shoot length. Reproductive growth parameters measured were cut flower yield, stem length, stem diameter, number of five-leaflet leaves per stem, number of flowers per stem, and stem fresh weight. The experiment designed 10 plants per treatment with two replications and the treatment plot was laid out in a completely randomized.

Statistical analysis

 Data collected were analyzed for statistical significance by the SAS (Statistical Analysis System, V. 9.1, Cary, NC, USA) program. The experimental results were submitted to an analysis of variance (ANOVA) and Duncan’s multiple range test. Graphing was performed with Sigma Plot 10.0 (Systat Software, Inc., San Jose, CA, USA).

Results and Discussion

 Exogenous treatment with cytokinins at the early stage of growth after transplanting had an effect on shoot length of ‘New Man’ (Figs. 1 and 2). In ‘New Man’, the greatest shoot length was found in the control plants relatively early transplanted at 0 day. The result is similar to those of Park and Jeong which (2011) reported that stem length of younger transplant was greater than older transplant. However, shoot length of ‘New Man’ transplanted at 7 days after application showed greater early stage growth in the 10mg·L^-1 kinetin treatment than in the control. This result suggested that exogenous treatment of cytokinins help plants to promote from shoot growth. Cytokinins from the roots may be involved in the regulation of shoot growth and development of Rosa hybrid (Dieleman et al., 1997). Cytokinins are translocated to the shoot from roots by xylem, where they regulate development and senescence processes. Earlier suggestions that increased root growth may lead to a corresponding increase in the synthesis of cytokinins (Alvim et al., 1974) have since been supported by the findings of Richards (1983). This, together with the higher levels of cytokinins in cocoa just prior to and after flush emergence (Orchard et al., 1981), when root growth is at its peak (Hardwick et al., 1982a), would tend to suggest that root growth is linked to the breaking of shoot dormancy through the activity of cytokinins. In cocoa, this appears to be further supported by the artificial breaking of dormancy with exogenous application of cytokinins (Abo-Hamed et al., 1981; Hardwick et al., 1982b).

Fig. 1. Shoot length measured for 3 weeks of spray rose ‘New Man’ as affected by cytokinins applied as a foliar-spray after transplanting. A, plants transplanted 0 day after application; and B, plants transplanted 7 days after application.

Fig. 2. Shoot length measured for 3 weeks of spray rose ‘New Man’ as affected by cytokinins applied as a drench after transplanting. A, plants transplanted 0 day after application; and B, plants transplanted 7 days after application.

 Shoot length of ‘New Lady’ was not different among treatments (Figs. 3 and 4). This suggested cultivar-specific responses that shoot length of ‘New Man’ showed the greater growth rate during the rooting stage than ‘New Lady’. Exogenous treatment with cytokinins at the early stage of growth after transplanting had no an effect on stem diameter of ‘New Man’ and ‘New Lady’ (data not shown).

Fig. 3. Shoot length measured for 3 weeks of spray rose ‘New Lady’ as affected by cytokinins applied as a foliar-spray after transplanting. A, plants transplanted 0 day after application; and B, plants transplanted 7 days after application.

Fig. 4. Shoot length measured for 3 weeks of spray rose ‘New Lady’ as affected by cytokinins applied as a drench after transplanting. A, plants transplanted 0 day after application; and B, plants transplanted 7 days after application.

 Stem length, number of flowers, and total fresh weight were significantly affected by cultivars (Table 1). Effect of cytokinin treatment on planting time of ‘New Man’ and ‘New Lady’ was not significant on stem length, fresh weight, and total stem weight, but number of five-leaflet leaves and flowers per stem. Growth of ‘New Man’ and ‘New Lady’ grown for about six months was not affected by cytokinin application method. Cytokinin treatment at transplanting time on growth of spray rose ‘New Man’ and ‘New Lady’ at first harvest time was not significantly affected (data not shown).

Table 1. Effect of cytokinin treatment at transplanting time on growth of spray rose ‘New Man’ and ‘New Lady’ grown for about six months.

 Stem length of ‘New Man’ was the greatest (69.2 cm) in the control when plants were transplanted at 7 days (Table 2). The greatest stem diameter (6.0 mm) was found in the 50 mg·L^-1 BA applied as a drench in plants transplanted at 0 day after application. On the whole, number of five-leaflet leaves per stem decreased with the exogenous treatment of cytokinins at the early stage of growth after transplanting. The result suggested that stem length decreased as number of five-leaflet leaves decreased when plants were applied with cytokinins at transplanting time. The result is opposite to those of Abdalla et al. (1985) reported that application of kinetin to Adonis autumnalis L. increased the plant height, stem diameter, fruit weight, and caused early flowering.

Table 2. Effect of cytokinin treatment at transplanting time on growth of spray rose ‘New Man’ grown for about six months.

 The greatest stem length (67.6 cm) and number of flowers (5.7) of ‘New Lady’ were found in the 50 mg·L^-1 BA applied as a drench in plants transplanted at 0 day after cytokinin application (Table 3). Total fresh weight increased as cytokinin treatments than in the control. Stem diameter and fresh weight were not affected by cytokinin application.

Table 3. Effect of cytokinin treatment at transplanting time on growth of spray rose ‘New Lady’ grown for about six months.

 Cut flower of roses were graded into 1^st, 2^nd, 3^rd, 4^th, and 5^th grades according to their stem length as ≥80, 79~70, 69~60, 59~50, and ≤49 cm, respectively (Table 4). In Korea, a cut rose stem greater than 60 cm considered as a high grade (Son, 1995). Cut flower yield by grade was affected by cultivar and planting time, but by not cytokinin application method and cytokinin type and concentration.

Table 4. Effect of cytokinin treatment at transplanting time on accumulated cut flower yield of spray rose ‘New Man’ and ‘New Lady’ grown for about six months.

 Cut flower yield by grade and total yield of ‘New Man’ and ‘New Lady’ was not affected by cytokinin application (Tables 5 and 6). This result is different from those of Hanada et al. (1994) who reported positive response of rice to cytokinin application. In a field trial, cytokinin application increased the yield of rice by 45.8% as compared to the control (Mayeux, 1983).

Table 5. Effect of cytokinin treatment at transplanting time on mean cut flower yield by grade and total flower yield of spray rose ‘New Man’ grown for about six months.

Table 6. Effect of cytokinin treatment at transplanting time on mean cut flower yield by grade and total flower yield of spray rose ‘New Lady’ grown for about six months.

 According to de Vries and Dubois (1989), in grafted rose plants the genotype of the rootstock influenced bud break of the scion, ultimately reflecting yield of cut flowers. Rootstock effects on shoot growth may be correlated with levels of cytokinins in xylem sap, as was shown for Vitis vinifera (Skene and Antcliff, 1972) and Prunus avium (Stevens and Westwood, 1984). Various cytokinins have been practically tested for the promotion of bottom break and rejuvenation of a rose crop (de Hoog Jr., 2001). Extensive studies have been conducted on the formation of cytokinins in various rootstock types and effect of this on the development of shoots. There were quantitative relations between the uptake of cytokinins from the root and development of the shoot, and between the genotype of the rootstock and cytokinin concentration in the bleeding sap.

 ‘New Man’, but not ‘New Lady’, had slightly promoted shoot growth at the early stage of growth after transplanting, but its productivity was affected by cytokinin application. Therefore, growth and early productivity of stenting-propagated ‘New Man’ and ‘New Lady’ are not promoted by the exogenously applied cytokinins at the transplanting stage. The control plants transplanted at 0 day, or with undamaged roots, are better in productivity as stenting-propagated roses than those transplanted at 7 days, or with senesced root tips. Propagated plants are rather recommended to be transplanted as soon as possible to avoid any damages to the root tips.