Efficacy of Growth Regulators on Flowering of Gerbera (Gerbera jamesonii B.) cv. Goliath in Open Field Condition

Gerbera (Gerbera jamesonii, B.) also known as ‘Transvaal Daisy’, ‘Barbeton Daisy’ or ‘African Daisy’ belonging to family Asteraceae occupies 5^th place as cut flower in international flower trade (Sujatha et al., 2002). It is popular because of its attractive colour, long vase life and suitability for long distant transport (Bose et al., 2003). It is used for fresh and dry flower arrangement, exhibition, decoration, bouquet preparation (Patra et al., 2015). Local and improved cultivar are grown in garden, flower bed, pots, borders, dish garden and rock garden. Flowers are of different colour like white cream, yellow, pink, orange, brick red, scarlet, salmon, maroon and bicolor and are available in single, semi-double or double form.

Application of plant bio regulators at specific concentration modify growth, flowering, flower yield and post harvest quality of flowers. Growth promoters like auxin, gibberellin and cytokinin modify physiological process by accelerating plant growth while growth retardant like cycocel and abscisic acid inhibit plant growth. Maximum vegetative  growth, flower yield and quality was observed in gerbera by application  of GA3 @ 150 ppm. (Dalal et al., 2009).

Similarly, application of growth retardant like paclobutrazole @ 25 to 100 ppm in gerbera reduce plant spread, increase leaf number/plant, increase chlorophyll content, decrease in stalk length, increase in stalk thickness, number of flowers and flower quality parameters (Bekheta et al., 2008).

The present study was conducted in premises of Biotechnology cum Tissue Culture Centre, Odisha University of Agriculture Technology, Bhubaneswar from Nov. to Oct. 2015-16 and 2016-17 in open condition.

The experimental site is situated 63 km away from Bay of Bengal at an altitude of 25 m above MSL and extended between 20°15' North latitude and 85°50' East longitude. The average rainfall of the site is 1646 mm. The maximum temperature during the experimental period was 38.8°C to 40.8°C and minimum temperature was 14.1°C to 15.2°C. The relative humidity during the experimental period was 37% to 94%. The experimental soil was sandy loam with pH 5.83, EC 0.64 ds/m, OC 0.475%, N 125 kg/ha, P₂O₅ 67.1 kg/ha, K₂O 166.6 kg/ha. The growing media was composed of soil, FYM and coco peat in 1: 1: 1 proportion.

Earthen pots with a hole at the bottom were used for planting. The pots were filled with soil mixture. Four leaved tissue culture plantlet of gerbera cv. Goliath a variety suitable for protected cultivation was used for planting. A basal dose of NPK @ 10:15:20 g per m² was applied. The experiment was laid down in completely randomized design (CRD) with nine treatments and three replication per treatments. There were 10 plants per replication and 30 plants per treatment making a total population of  270 plants.

The present experiment comprised with 9 treatments i.e. T₁ (Control), T₂ (GA3 @ 100 ppm), T₃ (GA3 @ 150 ppm), T₄ (Cycocel  @ 700 ppm), T₅ (Cycocel  @ 800 ppm), T₆ (GA₃ @ 100 ppm + amino acid @ 2 ml/l), T₇ (GA₃ @ 150 ppm + amino acid @ 2 ml/l), T₈ (Cycocel @ 700 ppm + amino acid @ 2 ml/l), T₉ (Cycocel @ 800 ppm + amino acid @ 2 ml/l).

For application of treatments to the plants following concentrations of plant bio regulators solution were prepared. With help of a precision balance 100 mg and 150 mg of GA₃ were measured and taken in two beakers separately. Little quantity of sodium hydroxide was added to the beaker for easy solubility. Then the volume was made to 1 litre by adding water in to the beakers thus preparing 100 ppm and 150 ppm of GA₃ solution.Similarly, 700 mg and 800 mg of cycocel were measured and taken in two beakers separately. Little quantity of alcohol was added to the beaker for easy solubility and then the volume was made to 1 litre by adding water into the beaker. Thus, 700 ppm and 800 ppm cycocel solution were prepared.

The observation were recorded from 5 randomly selected plant within each replication of treatment for different floral parameters like days taken to flower bud initiation after disbudding, days taken to flowering, stalk length, stalk thickness, number of flower/plant, flower diameter and bloom life. The data collected were analysed statistically following the method of Gomez and Gomez (1984) using one way ANOVA in CRD. A comparison of treatment means were done at 5% level of significance (P=0.05).

The result of the experiment obtained in the year 2015-16 and 2016-17 were pooled and presented under following headings.
 
Days to flower bud initiation after disbudding
 
After disbudding of all plants, the days taken to flower bud initiation was counted. The pooled  data from both the years showed that the days taken to flower bud initiation (8.83 days) was minimum in T₆ (GA @ 100 ppm+ amino acid) which was at par with T₂ (GA @ 100 ppm), T₇ (GA @ 150 ppm+ amino acid) and T₃ (GA @ 150 ppm) (Table 1). The earliness in flower bud initiation might be attributed to the fact that GA helps in auxin synthesis and enhance metabolism. Phengphachanh (2012) reported that GA application reduce ABA level in plant resulting early bud emergence. The maximum delay in flower bud initiation (22.08 days) was observed in treatment T₁ (control) where no growth regulator was applied. Similar finding was also observed by Dalal et al., (2009), Emongor et al., (2004) who reported early flower bud emergence by GA application.


 
Days to flowering
 
The days taken to flowering from flower bud emergence was counted. The earliest flowering (15.83 days) was recorded in T₆ (GA @ 100 ppm+ amino acid) which was at par with T₇ (GA @ 150 ppm + amino acid), T₂ (GA @ 100ppm) (Table 1). The earliness in flowering might be due to GA application at optimum concentration (100 ppm). Phengphachanh (2012) reported that application of GA reduce level of growth retardant (ABA) in gerbera resulting early flowering. Similar findings have been obtained by Awan et al., (1999), Nair et al., (2002), Rana et al., (2005), Matsumoto et al., (2006), Dalal et al., (2009) with respect to early flowering in gerbera. The maximum delay in flowering (23.50 days) was observed in treatment T₁ (control) due to no application of growth regulators.
 
Length of flower stalk
 
The pooled data from both the year revealed that in winter season longest stalk length (61.84 cm) was observed in T7 (GA @ 150 ppm+ amino acid) which was at par with T₃ (GA @ 150 ppm) while minimum stalk length (45.68cm) was observed in T₅ (Cycocel @ 800 ppm) (Table 1). Increase in stalk length in T₇ and T₃ might be due to application of GA @ 150 ppm with or without amino acid. Being a growth promoter Gibberellin induce cell elongation and cell enlargement increasing stalk length. Similar finding was obtained by Pobudkiewicz and Nowak (1992), Sujatha et al., (2009), Dalal et al., (2009), Dogra et al., (2012), Mehraj et al., (2013) and Jamaluddin et al., (2014) by application GA in gerbera. Decrease in flower stalk length in T₅ (Cycocel @ 800ppm) may be due to inhibitory effect of cycocel on cell elongation and cell enlargement which corroborates with the findings of Mohamed (1992) who reported that growth retardant like ethrel decreased stalk length. Similar trend in increase in length of flower stalk was also observed in summer and rainy season.
 
Thickness of flower stalk
 
The pooled data from both the year revealed that in winter season maximum stalk thickness (6.99 mm) was observed in T₉ (Cycocel @ 800 ppm + amino acid) which was at par with T₈ (Cycocel @ 700 ppm+ amino acid). Increase in stalk thickness in T₉ and T₈ might be due to application of cycocel and as a growth retardant it checks apical dominance and stem elongation but increases stem thickness.

Similar findings were also obtained by Lin (1961) and Muthumanickam et al., (1999) who stated that application of growth retardant like ethrel increased stalk thickness in gerbera. Thinnest flower stalk (5.17 mm) was observed in T₁ (control) during summer where no growth regulators was applied. Similar trend in increase in stalk thickness was also observed in winter and rainy season.

Number of flowers/plant
 
Pooled data from both the year revealed that in winter season maximum number of flowers (15.77/plant) was found in T₈ (Cycocel @ 700 ppm+ amino acid) which was at par with T₄ (Cycocel @ 700 ppm), T₆ (GA @ 100 ppm+ amino acid) and closely followed by T₉ (Cycocel @ 800 ppm+ amino acid while lowest number of flower (8.43/plant) was recorded in T₁ (Control).

Increase in flower number in T₈ and T₄ may be due to application optimum concentration of Cycocel @ 700 ppm with or without amino acid. Being a growth retardant cycocel inhibits apical dominance and induce bushiness/ dwarfness which resulted in emergence of more number of suckers. When number of suckers increased, the number of flower/plant increased. Similar finding have been obtained by Mohamed (1992), Muthumanikam et al., (1999) and Kumar et al., (2008) who reported increase in flower number by application of growth retardant like ethrel in gerbera. Besides, Cycocel application another treatment T₆ (GA @ 100 ppm+ amino acid) produced more number of flowers/plant which was very close to best treatment. Similar finding have been obtained by Nair et al., (2002), Sujatha et al., (2002), Dalal et al., (2009), Jamaluddin et al., (2013) in increasing number of flowers/plant in gerbera. The minimum number of flower/plant obtained in T₁ (Control) may be due to no application of growth regulator. Similar trend in increase in number of flowers/plant was also observed in summer and rainy season.
 
Flower diameter
 
The pooled data from both of the years revealed that in winter season largest flower diameter (11.53cm) was observed in T₈ (Cycocel @ 700 ppm + amino acid) which was at par with T₆ (GA3 @ 100 ppm + AA), T₉ (Cycocel  @ 800 ppm + AA) and T₄ (Cycocel @ 700 ppm) while minimum flower diameter (9.49cm) was observed in T₁ (control) (Table 2). Increase in flower diameter in T₈ and T₄ might be due to application of optimum concentration of cycocel @ 700 ppm with or without amino acid. Being a growth retardant cycocel result delay flowering which help in accumulation of photosynthates in plant resulting larger flower. Highest chlorophyll content in treatment with cycocel is also an evidence of maximum dry matter production resulting large flower. Similar findings have been obtained by Nair et al., (2002) by application of cycocel in gerbera. The role of growth retardant in increasing flower diameter was also proved by Mohamed (1992) with application of ethrel in gerbera. The smallest flower diameter was recorded in T₁ (control) which was due to no application of growth regulator in gerbera. Similar trend in increase in flower diameter was also observed in summer and rainy season.
 
Bloom life
 
The pooled data from both the years revealed that in winter season maximum bloom life (21.34 days) was observed in T₈ (Cycocel 700 ppm+ amino acid) which was closely followed by T₉ (Cycocel @ 800 ppm+ amino acid) while minimum bloom life (11.65 days) was observed in T₁ (control) (Table 2). Increase in bloom life might be due to application of cycocel. As discussed earlier, due to delay in flowering and more chlorophyll content in treatment with cycocel, there was more reserve of photosynthates in flower which prolong bloom life. Similar finding have been reported by Jamaluddin et al., (2014) by application of growth retardant like ethrel in gerbera. The shortest bloom life was observed in T₁ (control) due to no application of growth regulators. Similar trend in increase in bloom life was also observed in summer and rainy season.

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From the above findings it can be concluded that combination of GA3 @ 100 ppm and amino acid performed best with respect to days to flower bud initiation and flowering. Maximum stalk length was achieved by application of GA3 @ 150 ppm+ amino acid while maximum number of flowers/plant, diameters of flower and bloom life were observed by application of CCC @ 700 ppm + amino acid. Maximum stalk thickness was found in treatment with cycocel @ 800 ppm+ amino acid. The result of this study will be torch bearer for the researcher as well as gerbera grower for enhancing flower production under open field condition.