Pre-planting Exogenous Application of Gibberellic Acid Influences Sprouting, Vegetative Growth,...

Pre-planting Exogenous Application of Gibberellic Acid Influences Sprouting, Vegetative Growth, Flowering, and Subsequent

Bulb Characteristics of ‘Ad-Rem’ Tulip

Fahad Ramzan1,2, Adnan Younis1,2*, Atif Riaz1, Sajid Ali1, Muhammad Irfan Siddique1, and Ki-Byung Lim2

1Institute of Horticultural Sciences, University of Agriculture, Faisalabad, 38040, Pakistan2Department of Horticultural Science, Kyungpook National University, Daegu 702-701, Korea

*Corresponding author: [email protected]

Received September 2, 2014 / Revised October 6, 2014 / Accepted October 7, 2014Ⓒ Korean Society for Horticultural Science and Springer 2014

Abstract. Tulip (Tulipa gesneriana L.) is a fascinating bulbous cut flower, and also used for potting, bedding, and border purpose. However, under the sub-tropical climatic conditions, quality tulip flower production is severely affected by its non-uniform bulb sprouting, lack or erratic flowering, small flower stalk, and short vase life. Hence, this study was performed to evaluate the potential of gibberellic acid (GA3) on sprouting, vegetative growth, flowering, flower quality, and vase life, including different bulb characteristics of ‘Ad-Rem’ tulip. Tulip bulbs were dipped in aqueous solution of different GA3 concentrations (0, 50, 75, 100, 125, and 150 mg L-1) for 30 min with Tween-20 (0.01%) as a surfactant. Tulip bulbs treated with 100 mg·L-1 GA3 sprouted in significantly less number of days, exhibited higher sprouting percentage, more plant height, leaf area, leaf chlorophyll, photosynthesis rate, flower stalk length, stalk diameter, and fresh and dry flower stalk weight. Moreover, 100 mg·L-1 GA3 application also decreased overall flower emergence time, increased flower size, produced attractive, glowing, and sturdy flowers with increased quality, and extended the vase life of ‘Ad-Rem’ tulip flowers up to 2.9-folds. However, 150 mg·L-1 GA3 application exhibited better results regarding daughter bulblets per clump with a subsequent increase in bulb diameter, and weight compared to other treatments. Additionally, significant correlation was also found among different growth, flower, and bulb characteristics of GA3-treated tulip plants. Hence, 100-150 mg·L-1 pre-planting exogenous application of GA3 may be effective for quality tulip production under the sub-tropical climatic conditions.

Additional key words: days to sprouting, flower quality, Tulipa gesneriana, vase life

Hort. Environ. Biotechnol. 55(6):479-488. 2014.DOI 10.1007/s13580-014-0113-7

ISSN (print) : 2211-3452ISSN (online) : 2211-3460

Research Report

Introduction

Tulip (Tulipa gesneriana L.), is a fascinating bulbous flowering plant that belongs to the family Liliaceae. Tulips are also used as potting, bedding, and border plants around the globe. It has now become one of the most imperative ornamental crops due to its wide availability of cultivars, attractive color range, and beautiful flowers. Moreover, it is the 4th major cut flower in the global floriculture trade (Jhon and Neelofar, 2006).

For profuse flowering, the majority of the bulbous plants need a phase of cold temperature exposure, and this coldness is generally provided by the severe winter conditions in tem-perate regions of the world (De Hertogh and Le Nard, 1993). However, the requirements of the cold winter conditions may be shortened or even substituted by a fine exhausted, low

temperature management of dry stored bulbs through forcing technique in non-temperate areas. Among various other bulbous flowers, tulip bulbs also require a cold period of low temperature treatment/exposure for proper flowering, and flower stalk elongation (De Hertogh and Le Nard, 1993). During the cold period exposure some growth promoting hormones are produced that play a valuable part in the development of flower buds (Saniewski and De Munk, 1981). Low temperature storage of bulbs has been reported to manage low temperature requirements of some bulbous flowers. Besides low temperature storage, some specific plant growth regulators (PGRs) can also be applied exogenously on dif-ferent plant parts which not only shorten or substitute cold temperature/chilling requirements, but also influence normal development of different ornamental plants (Al-Khassawneh et al., 2006; Rees, 1992). Moreover, exogenous application

Fahad Ramzan, Adnan Younis, Atif Riaz1, Sajid Ali, Muhammad Irfan Siddique, and Ki-Byung Lim480

Fig. 1. Monthly metrological data during 2011-2012. Temperature is given in the form of average of both maximum, and minimum during a particular month.

of different PGRs has also been reported to play pivotal role in the manipulation of vegetative growth, uniform flowering, and subsequent bulb production in various flowering crops. Among various PGRs, gibberellins are involved in numerous plant developmental progressions; promote leaf area, flower stalk elongation, early and uniform flowering as well as in-creased flower size (Al-Khassawneh et al., 2006). Gibberellins also influence vital physiological changes including cell di-vision, cell expansion, induction, and promotion of flowering (Vieira et al., 2010).

Among different gibberellins, gibberellic acid (GA3) has been known to break dormancy of seeds, bulbs, and tubers. Moreover, it has also been emerged as a prominent source for the replacement of low temperature phase of bulbous plants with simple exogenous application that might decrease or even prevent the requirements of costly cold storage of bulbs, and also decreases or even completely eradicate the low temperature/chilling requirements (Rees, 1992). Moreover, GA3 also increases floral buds, flower stalk length, and results in early, and profuse flowering of Azalea, Impatiens, Iris nigricans, and Aglaonema sp. Likewise, the effective role of GA3 has also been reported in some species of Hyacinthus, Lilium, Iris, Liatris, Rhododendron, and Muscari as an alternative for the low temperature requirements (Vieira et al., 2010). Different methods of GA3 application include soaking of bulbs before planting, and foliar spray at different growth stages. However, soaking of bulbs before planting is considered advantageous over the foliar application; for instance, it saves time, labor, and overall production expenses (Ranwala et al., 2002). Moreover, dip treatment in the form of ‘quick-dip’ application of GA3 has been reported in Zantedeschia hybrid tubers (Dennis et al., 1994). Although some reports are available in literature regarding the use of GA3 in tulip, but information regarding improvisation of GA3, as a pre-planting dip treatment on sprouting, on growth, flowering, and different bulb characteristics of tulip under the sub-tropical climatic conditions is lacking.

Therefore, we hypothesized that GA3 may be effective to manage different problems of tulip and we investigated the potential of GA3 as pre-planting dip application on the sprouting of bulbs, vegetative growth, flowering, flower quality, flower stalk length, vase life, and subsequent bulb characteristics of tulip.

Materials and Methods

Cultural Conditions and Experimental DesignThis research was conducted at the lath house of Flo-

ricultural Research Area, Institute of Horticultural Sciences (latitude 31°30'N, longitude 73°10'E and altitude 213 m), University of Agriculture, Faisalabad, Pakistan during

2011-2012. The experiment was laid out under randomized complete block design (RCBD), and twenty bulbs were planted in each treatment with four replications. Before conduct of the research work, soil samples from various blocks of the experimental field were collected to assess its physico-chemical properties. Soil of the experimental site was slightly alkaline in nature (pH 8.79), with 0.65% organic matter, and electrical conductivity was 2.47 dS·m-1. Similarly, soil nitrogen (N), phosphorous (P), and potassium (K) were 11.57%, 9.6 mg·kg-1, and 184 mg·kg-1, respectively. Monthly meteorological data during crop season (2011-2012) is given in Fig. 1. After soil sampling, soil was thoroughly tilled, leveled, all the undesirable debris of weeds was removed, and uniform cultural practices were followed before, and after planting of tulip bulbs in all treatments including the control.

Planting Material and Treatments Bulbs of Tulipa gesneriana L. ‘Ad-Rem’ were procured

from Green works Pvt. Limited, Lahore, Pakistan, an importer of Stoop Flower Bulb Company, Netherlands, while source of GA3 was Bio-World, Dublin, Ohio, USA. On arrival, bulbs were kept in the laboratory at 25 ± 2°C for a period of one week to acclimatize before actual planting. GA3 was dissolved in 0 (control), 50, 75, 100, 125 or 150 mg·L-1 concentrations (0.01% Tween-20 was also added in GA3 solution as sur-factants), and was applied on bulbs by pre-plant bulb dipping method for 30 min in a solution of water. The bulbs were planted during winter season (duration of the winter season in Pakistan is from November to February-March) on ridges with P × P and R × R spacing of 20 and 60 cm, respectively. All the cultural practices for instance weeding, earthing up, and plant protection measures were same for all treatments including the control during the entire period of study.

Bulb Sprouting and Vegetative Growth Physiognomies Days to sprouting were recorded from the time of planting

Hort. Environ. Biotechnol. 55(6):479-488. 2014. 481

to sprouting. Sprouting percentage was recorded by the fol-lowing formula when all the bulbs had sprouted, and expressed in percentage:

Plant height of ten tulip plants was measured in cm with the help of measuring scale from base of the plant to the top edge of the leaf, and their average was calculated. Number of leaves of ten randomly selected plants was counted manually after 70 days of planting, and average was calculated. Two fully developed mature leaves from ten plants per treatment were sampled; their area was measured according to the method, as described by Carleton and Foote (1965) with following formula:

Leaf area (cm2) = maximum length × maximum breadth × 0.68

For the determination of leaf chlorophyll contents, ten leaf samples from each treatment were collected and chlo-rophyll contents were measured with the help of chlorophyll meter (SPAD-502) after its calibration, and their average was calculated. Photosynthetic rate was measured with the help of infrared gas analyzer (IRGA, Analytical Development Company, Hoddesdon, England) using two leaves of ten randomly selected tulip plants. Fresh weight of ten tulip leaves was weighed on a weight balance. Ten samples per treatment were weighed, and their average was computed. Leaves were then placed in an oven at 72ºC and weighed again after 72 hours to record their dry weight.

Flower CharacteristicsDays to flower emergence were recorded from the time of

planting to emergence of floral buds on the plants. Days to flower opening were recorded from the time of harvesting till the opening of the flowers. Tulip flower size (cm) was measured with the help of measuring scale when its flowers were fully opened in north-south, and east-west directions of ten randomly selected flowers. Flower stalk length (cm) of ten randomly selected plants was measured with the help of measuring tape; average was computed. The flower stalk diameter (mm) of ten randomly selected plants was measured with a digital vernier caliper (CD-6 CSX, Mitutiyo, Kawasaki, Japan), averaged from five different points of the stalk. Ten flowers were weighed at harvest to record the fresh weight (g). Ten samples per treatment were weighed, and their average was calculated, and expressed in g. After weighing flowers, flower stalks were placed in an oven at 72°C for 72 hours. After this, flowers were taken out, and weighed again to record their dry weight. In this way, dry weight of flowers was recorded after computing the average in g. Flower quality was determined on a rating scale from 1-9. The highest rating for best quality, uniform, and sturdy flowers was 9, while, scale 5 was used for medium, average quality flowers, and scale 1 were used for lanky, weak, and poor quality flowers.

Tepal diameter (mm) was measured by a digital vernier caliper (CD-6 CSX, Mitutiyo, Kawasaki, Japan) from the middle of the lower mast floret when it just started to show its color. Ten samples from each treatment were recorded. The flowers were harvested when the perianth started showing color, immediately were put in buckets containing distilled water, and were shifted to the laboratory. Leaves of the floral stalks were removed, and placed separately in glass vases having 300 mL of distilled water. After every two days, vase water was replaced with fresh distilled water, and lower 2.5 cm of the stems was removed with a sharp shear to get rid of physiological plugging of the stems. Ten randomly selected flowers per treatment were used for vase life evaluation. Flowers were considered dead when more than 50% were dried or faded.

Bulb CharacteristicsThe number of daughter bulblets produced per clump was

recorded from ten tulip plants under study from each treat-ment, and the average was calculated. Average diameter (mm) of bulblets was recorded with a digital vernier caliper. Bulblets produced per clump were washed thoroughly, weighed on a balance in average weight was calculated, and expressed in g.

Statistical AnalysisThe collected data were analyzed statistically according

to Fisher’s analysis of variance (ANOVA) technique, and Duncan’s New Multiple Range test was used for the com-parison of different treatment means at p ≤ 0.05 (Steel et al., 1997) with computer based MSTAT-C software. Pearson correlations were also calculated with the same software to determine the relationship between different parameters of GA3-treated tulip plants.

Results

Bulb Sprouting and Vegetative GrowthDipping of bulbs in GA3 solutions substantially affected

different bulb, and vegetative characteristics of ‘Ad-Rem’ tulip. Among the treatments, 100 mg·L-1 GA3-treated bulbs sprouted earlier (37.67 days) as compared to the controls (Table 1). Dipping of GA3 significantly (p ≤ 0.05) improved the sprouting percentage of Ad-Rem’ tulip bulbs (Table 1). The GA3-treated-bulbs exhibited high sprouting percentage than the control. However, bulb treated with 100 mg·L-1 GA3 exhibited highest (1.5-fold) percentage of sprouting than the untreated bulbs (Table 1). Plant height was found significantly (p ≤ 0.05) more in the treated bulbs as compared to the control. Application of 100 mg·L-1 GA3 resulted in maximum (26.21 cm) plant height than the control plants


Table 1. Effects of pre-planting gibberellic acid (GA3) application on days to sprouting, sprouting percentage, plant height, and number of leaves per plant of tulip ’Ad-Rem’.

Treatment Days to sprouting

Sprouting(%)

Plant height(cm)

No. of leaves/plant

Control 57.11 a 66.73 e 12.10 b 3.00 d50 mg·L-1 GA3 53.67 b 76.68 d 15.64 ab 3.11 bc75 mg·L-1 GA3 47.89 d 84.22 c 19.09 ab 3.22 b100 mg·L-1 GA3 37.67 f 97.76 a 26.21 a 3.44 a125 mg·L-1 GA3 41.00 e 90.53 b 21.09 ab 3.44 a150 mg·L-1 GA3 50.56 c 79.51 d 16.40 ab 3.22 bLSD (p ≤ 0.05) 2.619 4.224 3.882 0.723

Values are the means of 10 tulip plants per treatment. Mean values within columns followed by different letters are significantly different according to Duncan’s new multiple range test (p ≤ 0.05).

Fig. 2. Effects of pre-planting gibberellic acid (GA3) application on photosynthesis rate, leaf chlorophyll content, and leaf area of tulip ‘Ad-Rem’. Vertical bars represent standard error of means (n = 4).

(12.10 cm) (Table 1). Number of leaves per plant was also greater in the GA3-treated bulbs as compared to the control. However, 100 mg·L-1 GA3 application exhibited 1.15-folds more leaves than the control (Table 1). The level of photo-synthetic rate was also increased with the exogenous application of different concentration of GA3. However, unlike plant height and number of leaves, bulbs-treated with 125 mg·L-1 GA3 exhibited higher (1.5-fold) photosynthesis rate as com-pared to the control (Fig. 2A). Besides the photosynthesis rate, exogenous application of GA3 also significantly (p ≤ 0.05) exhibited higher leaf chlorophyll contents. However, the most pronounced increment (1.30-fold) was found in the bulbs treated with 100 mg·L-1 GA3 than the control (Fig. 2B). Similarly, significant differences were also found regarding leaf area of ‘Ad-Rem’ tulip, and the maximum leaf area was found in the bulbs treated with 100 mg·L-1 GA3 (147.75 cm2) as compared to the control (Fig. 2C). Exogenous ap-plication of GA3 also increased both leaf fresh and dry weight of tulip plants. However, unlike leaf area, ‘Ad-Rem’ tulip bulbs-treated with 125 mg·L-1 GA3 exhibited highest leaf fresh (3.40-fold), and dry weight (2.41-fold), as compared to the control (Table 2).

Flower CharacteristicsExogenous application of GA3 significantly (p ≤ 0.05)

decreased days to the emergence of flowers in all treatments. However, bulbs-treated with 100 ppm GA3 were emerged in substantially less number of days (91.89 days) (118.11 days) (Table 2). Moreover, in the control treatment, flowers not only emerged in more number of days, but flowers also did not open profusely. Pre-planting exogenous application of GA3 significantly affected ‘Ad-Rem’ tulip flower opening in all treatments. However, unlike flower emergence, bulbs treated with 75 mg·L-1 GA3 opened in the least number of days (2.64) compared to the control (Table 2). Although flowers were opened in less number of days in 75 mg·L-1


Table 2. Effects of pre-planting gibberellic acid (GA3) application on fresh and dry leaf weight and days to flower emergence and flower opening of tulip ’Ad-Rem’.

Treatment Fresh leaf weight(g)

Dry leaf weight(g)

Days to flower emergence

Days to flower opening

Control 1.97 b 0.41 b 118.11 a 5.78 a50 mg·L-1 GA3 1.79 b 0.56 ab 110.22 b 5.22 a75 mg·L-1 GA3 5.39 ab 0.68 ab 103.89 c 2.64 c100 mg·L-1 GA3 4.69 ab 0.60 ab 91.89 e 2.78 c125 mg·L-1 GA3 6.70 a 0.88 a 98.78 d 2.67 b150 mg·L-1 GA3 2.76 b 0.54 ab 106.89 c 3.00 bLSD (p ≤ 0.05) 3.491 0.345 4.440 0.739


Fig. 3. Effects of pre-planting gibberellic acid (GA3) application on flower stalk diameter, and flower stalk length of tulip ‘Ad-Rem’.Vertical bars represent standard error of means (n = 4).

treated plants, ‘Ad-Rem’ tulip flowers were opened uniformly in bulbs treated with 100 ppm GA3. Pre-planting exogenous application of GA3 also significantly (p ≤ 0.05) increased both flower stalk diameter, and length in all treated-plants than control. However, bulbs treated with 100 mg·L-1 GA3 exhibited highest stalk diameter (1.41-fold) as well as stalk length (1.51-fold) as compared to the control (Figs. 3A and 3B). Besides flower stalk diameter and stalk length, exogenous application of GA3 also significantly increased both fresh and dry flower stalk weight in all treated-plants. But, Ad-Rem’ tulip treated with 100 mg･L-1 GA3 excelled with maximal

fresh (2.79-fold) and dry (2.26-fold) stalk weight as compared to the control (Table 3). Similarly, exogenous GA3 application substantially influenced fresh and dry flower weight. However, among the treatments, bulbs-dipped in 125 mg·L-1 GA3 solution excelled with peak fresh (1.50-fold) and dry (2.44-fold) flower weight, respectively, as compared to the control (Table 3). Unlike to fresh and dry flower weight, maximum flower size was attained in tulip plants dipped in 100 mg·L-1 GA3 as compared to the control (Table 4). Moreover, this flower size was 1.40 folds higher than the control. Similarly, ex-ogenous application of GA3 significantly improved the flower tepal diameter. However, ‘Ad-Rem’ tulip bulbs treated with 125 mg·L-1 GA3 exhibited highest tepal diameter (1.88- fold) than the control (Table 4). Likewise, exogenous ap-plication of GA3 also increased the quality of ‘Ad-Rem’ tulip flowers. However, most remarkable quality flowers were found in bulbs treated with 100 mg·L-1 GA3 (6.78 score) with attractive, glowing, and sturdy flowers in contrast to the control (Table 4). Exogenous GA3 application also en-hanced the vase life of all treated-tulip flowers, but maximum increment in vase life extension was exhibited in bulbs dipped in 100 mg·L-1 GA3 (2.92-fold) as compared to the control which was characterized with least flower vase life (Table 4).

Bulb CharacteristicsPre-planting exogenous application of GA3 remarkably

influenced different bulb characteristics of ‘Ad-Rem’ tulip in all treated plants. However, unlike to various sprouting, vegetative, and flower characteristics, dipping of ‘Ad-Rem’ tulip in 150 mg·L-1 GA3 solution significantly increased (1.56) the number of daughter bulblets per clump in contrast to control (Table 5). Moreover, these bulbs were also healthier and bigger in size than the control. Similarly, exogenous application of GA3 substantially increased the diameter of ‘Ad-Rem’ tulip bulbs. However, among the treatments, bulblet diameter was higher in bulbs-dipped in solution of 150


Table 3. Effects of pre-planting gibberellic acid (GA3) application on fresh and dry flower stalk weight, and fresh and dry flower weight of tulip ’Ad-Rem’.

Treatment Fresh stalk weight(g)

Dry stalk weight(g)

Flower fresh weight(g)

Flower dry weight(g)

Control 3.74 d 0.43 d 23.04 e 2.61 d50 mg·L-1 GA3 3.97 d 0.52 d 25.11 d 3.38 cd75 mg·L-1 GA3 6.63 bc 0.75 bc 27.13 c 4.03 bc100 mg·L-1 GA3 10.43 a 0.97 a 32.43 b 4.68 b125 mg·L-1 GA3 7.61 b 0.85 ab 34.64 a 6.37 a150 mg·L-1 GA3 4.76 cd 0.59 cd 25.49 d 3.82 bcLSD (p ≤ 0.05) 2.043 0.199 1.504 0.869


Table 4. Effects of pre-planting gibberellic acid (GA3) application on flower size, tepal diameter, flower quality, and vase life of tulip ’Ad-Rem’.

Treatment Flower size(cm)

Tepal diameter(mm)

Flower quality(score)

Vase life (day)

Control 4.71 c 5.53 d 4.75 c 3.00 e50 mg·L-1 GA3 5.38 b 6.34 c 4.92 c 4.22 d75 mg·L-1 GA3 5.42 b 7.03 b 5.24 b 6.88 b100 mg·L-1 GA3 6.59 a 8.92 b 6.78 a 8.77 a125 mg·L-1 GA3 6.22 a 10.38 a 6.56 a 7.22 b150 mg·L-1 GA3 5.91 b 6.57 c 5.34 b 5.11 cLSD (p ≤ 0.05) 0.867 1.187 0.893 0.772

Values are the means of 10 tulip plants per treatment. Mean values within columns followed by different letters are significantly different according to Duncan’s New Multiple Range test (p ≤ 0.05).

Table 5. Effects of pre-planting gibberellic acid (GA3) application on different bulb characteristics of tulip ’Ad-Rem’.

Treatment Number of bulblets/clump Bulblet diameter (mm)

Bublet weight (g)

Control 2.56 d 16.95 c 4.04 d50 mg·L-1 GA3 2.78 cd 22.40 b 4.31 d75 mg·L-1 GA3 3.44 abc 24.45 b 5.40 c100 mg·L-1 GA3 3.11 bcd 23.98 b 4.36 d125 mg·L-1 GA3 3.78 ab 30.70 a 6.90 b150 mg·L-1 GA3 4.00 a 35.09 a 8.62 aLSD (p ≤ 0.05) 0.742 5.316 0.940


mg·L-1 GA3 (2.07-fold) followed by 125 mg·L-1 GA3 (1.81-fold) in contrast to the control (Table 5). Regarding bulblet weight is concerned, it was proved to depend substantially on GA3 application as bulbs of tulip cv. Ad-Rem dipped in 150 mg·L-1 solution of GA3 excelled with comparatively higher weight of bulblets (2.13-fold) than the control (Table 5).

Relationship between Different Vegetative, Flower and Bulb Characteristics of GA3-treated Plants

Strong positive correlation was found among most of the parameters under study. Bulb diameter was significantly (p ≤ 0.01) correlated (r = 0.88) with bulblets weight (Table 6). Similarly, significant positive correlation was also found


Table 6. Correlation of various characteristics of tulip ’Ad-Rem’ as affected by pre-planting gibberellic acid (GA3) application.

BD DFW DSW FFW FLW FSW LA LCC LDW NB PH FSD FSL FS VLDFW 0.67**SDW 0.65** 0.67**FFW 0.80** 0.92** 0.81**FLW 0.45NS 0.50* 0.55* 0.56*FSW 0.74** 0.59** 0.92** 0.77** 0.58*LA 0.77** 0.65** 0.92** 0.83** 0.55** 0.88**LCC 0.58* 0.60** 0.41NS 0.60** 0.25NS 0.38NS 0.38NS

LDW 0.31NS 0.53* 0.56* 0.55* 0.83** 0.48* 0.49* 0.38NS

NB 0.79** 0.72** 0.87** 0.78** 0.59** 0.82** 0.86** 0.42NS 0.53*PH 0.74** 0.46NS 0.60** 0.61** 0.65** 0.78** 0.92** 0.49* 0.44NS 0.80**FSD 0.64** 0.46NS 0.74** 0.65NS 0.23NS 0.69** 0.75** 0.51* 0.44NS 0.67** 0.56*FSL 0.75** 0.75** 0.82** 0.84** 0.37NS 0.75** 0.84** 0.67** 0.41NS 0.75** 0.61** 0.72**FS 0.87** 0.64** 0.74** 0.83** 0.32NS 0.77** 0.87** 0.51* 0.29NS 0.75** 0.57* 0.79** 0.88**VL 0.83** 0.67** 0.84** 0.83** 0.60** 0.86** 0.59** 0.48* 0.49* 0.58* 0.75** 0.75** 0.79** 0.86**BW 0.88** 0.62** 0.78** 0.84** 0.53* 0.87** 0.89** 0.46NS 0.40NS 0.76** 0.76** 0.70** 0.78** 0.89** 0.89**

BD, bulblets diameter; DFW, dry flower weight; DSW, dry stalk weight; FFW, fresh flower weight; FLW, fresh leaf weight; FSW, fresh stalk weight; LA, leaf area; LCC, leaf chlorophyll content; LDW, leaf dry weight; NB, number of bulbs per clump; PH, plant height; FSD, flower stalk diameter; FSL, flower stalk length; FS, flower size; VL, vase life; and BW, bulblet weight.NS,*,**Nonsignificant, significant at 5%, and 1%.

between dry flower weight, and fresh flower weight (r = 0.92). Likewise, dry stalk weight was significantly correlated with fresh stalk weight (r = 0.92) and leaf area (r = 0.92). Fresh flower weight was also significantly and positively correlated with stalk length (r = 0.84). Moreover, fresh leaf weight also revealed significant (p ≤ 0.01) positive correlation (r = 0.83) with leaf dry weight. Likewise, fresh stalk weight also ex-hibited strong positive correlation with leaf area (r = 0.88) followed by bulblets weight (r = 0.87). In case of leaf area, it was significantly and positively correlated with the height of tulip plants (r = 0.92). Leaf chlorophyll contents were also significantly correlated with stalk length (r = 0.67) of tulip flowers. Leaf dry weight was positively correlated (p ≤ 0.05) with number of bulbs (r = 0.53) per clump. On the other hand, the number of daughter bulblets per clump were significantly (p ≤ 0.01) correlated (r = 0.80) with plant height. On the other hand, plant height was significantly positively correlated (r = 0.76) with weight of bulblets. Likewise, flower stalk diameter was significantly (p ≤ 0.01), and positively correlated with flower size (r = 0.79), whereas, flower stalk length was also positively, and significantly (p ≤ 0.01) cor-related with flower size (r = 0.88). Flower size and vase life exhibited significantly positive correlations with weight of bulblets (r = 0.89).

Discussion

Bulb Sprouting and Vegetative Growth Physiognomies

Number of days required for sprouting and germination percentage is an important parameter for bulbous flowers. In the present study, exogenous GA3 application significantly reduced the mean sprouting time with increased sprouting percentage in ‘Ad-Rem’ tulip bulbs (Table 1). Early sprouting in GA3-treated bulbs may be ascribed to its suppressing effects on some growth inhibitors specially ABA contents which results in delayed, and non-uniform sprouting in tulip bulbs (Geng et al., 2007). Moreover, GA3 activates α-amylase enzyme that stimulates the hydrolyzaton of stored starch into simple sugars, and provides energy during germination of seeds or sprouting of bulbous crops (Hopkins and Huner, 2004; Kucera et al., 2005). Consequently, it enhanced the sprouting of ‘Ad-Rem’ tulip bulbs in relatively short time period. Growth is an important indicator that plays a pivotal role to obtain premium yield, and plant height is considered as the basic and key criteria indicating the normal plant growth. The GA3 application also significantly enhanced the height of treated ‘Ad-Rem’ tulip plants (Table 1) and sig-nificantly (p ≤ 0.01) and positively correlated (r = 0.76) with weight of bulblets (Table 6). The increase in plant height of tulip plant with the exogenous application of GA3 might be associated with the role of GA3 in increased cell division,


and cell elongation (Hartmann et al., 1989). Similarly, De Mello et al. (2009) also reported that GA3 reduced mean germination time, and increased the germination percentage in Penstemon digitalis.

Similarly, leaf chlorophyll contents, and photosynthesis rate were also significantly improved after GA3 application in ‘Ad-Rem’ tulip plants (Figs. 2A and 2B). Moreover, leaf chlorophyll contents were positively and significantly (p ≤ 0.01) correlated with stalk length (r = 0.67) of tulip flowers (Table 6). The possible reason for the increased chlorophyll contents is that GA3 emboldens the enrichment of plastids with ultra-structural morphogenesis, which leads to chlorophyll synthesis, conservation, and ultimately plant senescence is stopped and leaves were remained actively involved in pho-tosynthesis (Ouzounidou and Ilias, 2005). Similarly, GA3 can increase growth rate by increasing the leaf area, photosynthesis, photosynthate partitioning and/or their combinations (Ghorbanli et al., 1999). Moreover, GA3 is effective to prevent deg-radation of chloroplast, and chlorophyll that ultimately results in the increased chlorophyll content, and decreased leaf se-nescence of Alstroemeria flowers (Jordi et al., 1994). Similar to our findings, Emami et al. (2011) also reported increased leaf chlorophyll contents of lily in response to GA3 application in combination with benzyladenine. Besides other traits, the exogenous GA3 application also substantially increased the leaf area of treated-plants (Fig. 2C). There was also significant (p ≤ 0.01) positive correlation (r = 0.92) between leaf area and plant height during the growth, and development of tulip plants (Table 6). This increase in leaf area may be attributed to more cell division and cell enlargement by GA3 application (Hartmann et al., 1989). Besides increasing leaf area, fresh and dry weight of ‘Ad-Rem’ tulip leaves was also increased significantly (Table 2). It was possibly improved significantly due to biomolecules accrual responsible for the larger and thickened leaves owing to rapid cell division, and succeeding leaf enlargement. Similar to our findings, El-Naggar et al. (2009) reported that GA3 application increased fresh and dry biomass of Dianthus leaves.

Flower CharacteristicsFlower emergence was also significantly affected by pre-

planting exogenous GA3 application (Table 2) and, besides decreased flower emergence time, flowers also emerged uni-formly. Uniform flower emergence and opening are imperative for successful single possible harvesting to reduce overall production cost, and increased profit margin for the growers. In general, flowering in plants usually related with the hormonal as well as sugar changes. A transition progression from veg-etative growth to reproductive phase usually proceeds in response to certain environmental factors as these factors usually exert infusive effects by subsequently inducing various changes in the hormones (decreases levels of ABA), and sugar

levels (GA3 activates α-amylase enzyme that degrade starch into simple sugars) within the plants. Similar to our findings, Abou-Taleb and Kandeel (2001) and Al-Khassawneh et al. (2006) also reported decreased flower emergence time of Iris tingitana, and Iris nigricans, respectively.

Short flower stalk is one of the major problems in tulips. However, in the present study GA3 dipping remarkably in-creased both flower stalk length as well as stalk diameter of ‘Ad-Rem’ tulip flowers (Figs. 3A and 3B) and were also significantly (p ≤ 0.01) and positively correlated (r = 0.88 and r = 0.79) with flower size (Table 6). The increased flower stalk length, and diameter were possibly attributed to increased cell division, and cell enlargement that not only resulted in more stalk length, but also increased diameter as reported in ‘Cassini’ tulip by Khan et al. (2007). Similarly, fresh and dry stalk weight is considered a crucial factor for high yield in relation to plant growth. Exogenous GA3

application significantly increased both fresh and dry flower stalk weight in our case (Table 3). The GA3 improves length, and width of flower stalk due to prompt cell division besides cell elongation (Huttly and Philips, 1995). Therefore, its application resulted in improved fresh and dry flower stalk weight of ‘Ad-Rem’ tulip. Similar to our results, Younis et al. (2012) also reported increased fresh and dry biomass of Freezia flowers. Pre-planting GA3 application also substantially increased fresh and dry flower weight in ‘Ad-Rem’ tulip (Table 3). A significant (p ≤ 0.01) positive correlation (r = 0.92) was also found between dry and fresh flower weight (Table 6). Additionally, fresh flower weight was also sig-nificantly (p ≤ 0.01) and positively correlated (r = 0.84) with flower stalk length (Table 6). The increased fresh as well as dry weight was possibly attributed to increased tepal diameter, and comparatively more flower size indorsed by GA3. The GA3 possesses invigorating effects mainly on biochemical, and physiological aspects of plant that ultimately affects overall development as well as growth pattern. Consequently, such growth stimulating effects result in the alteration of plant flowering phase. The GA3 increased the number of flowers per inflorescence which finally leads to increased fresh and dry flower weight (Hassanpouraghdam et al., 2011). Similar to our findings, Abou-Taleb and Kandeel (2001) also found increased flower weight due to relatively more flower size of Iris tingitana in response to GA3 application. The GA3 also increased size and tepal diameter of ‘Ad-Rem’ tulip flowers (Table 4). It usually enhances both flower size, and diameter by making sink at a particular point where it usually draws as well as accumulates the available photo-synthates (Kuiper, 1993) that eventually results in the increased flower size, and diameter. Moreover, flower size was signif-icantly (p ≤ 0.01), and positively correlated (r = 0.89) with the weight of bulblets (Table 6). Likewise, Baskaran and Misra (2007) and Younis et al. (2014) also reported similar


increased flower diameter in Gladiolus, and Dahlia, respectively. Pre-planting application of GA3 also resulted in increased flower quality, and vase life of ‘Ad-Rem’ tulip (Table 4). During postharvest period of flowers several reactive oxygen species (ROS) are produced that ultimately lead to rapid senescence of flowers, and short vase life. However, GA3

induces increased production of catalase, and superoxide dismutase enzymes (Ducic et al., 2003) which prevent flowers from the damages caused by ROS and possibly increased the vase life. Moreover, our findings also corroborate the results of Delvadia et al. (2009) who reported that GA3 application significantly increased the vase life of Gaillardia pulchella flowers.

Bulb CharacteristicsIn case of different bulb characteristics, GA3 treatment

substantially increased the number of daughter bulblets per clump, bulb diameter, and weight (Table 5). Moreover, bulb diameter, and number of daughter bulbs per clump were significantly (p ≤ 0.01) and positively correlated (r = 0.88 and r = 0.80) with bulblets weight, and plant height, respectively (Table 6). Increased bulblets per clump, bulb size, and weight were possibly due to rapid cell division, and cell enlargement in response to GA3 application (Hartmann et al., 1989; Karuna et al., 2011). Moreover, photosynthetic metabolite partitioning is also very imperative because it generally relies on the suitable assimilation rate of photo-synthates from the source leaves, and their timely export to desired points (Komor, 2000). Therefore, export or accumulation of vital food reserves from tulip leaves was another possible reason for increased bulb size, bulblets/clump, and enhanced bulb weight in our case. Due to GA3 application food reserves increase at critical stages that ultimately lead to increased daughter bulblets per clump, diameter, and weight (Karuna et al., 2011). Moreover, similar to our findings, Mahesh and Misra (1993) also found increased size, and number of cormels in gladiolus.

Conclusion

In summary, pre-planting dipping of bulbs in GA3 solution significantly increased sprouting, vegetative growth; flowers stalk length, flower biomass, flower quality, and vase life. Moreover, it also proved to be effective to decrease overall flower emergence time, resulted in uniform flower opening with subsequent increased bulb size, and bulblets/clump. Therefore, dipping of bulbs in 100-150 ppm solution of GA3 is suggested to maximize quality tulip production under the sub-tropical climate of Punjab, Pakistan, and countries with similar climatic conditions.

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Pre-planting Exogenous Application of Gibberellic Acid Influences Sprouting, Vegetative Growth,...

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