Response of different plant growth regulators on growth, flowering and yield of african marigold (Tagetes erecta L.)

Introduction

Marigold (Tagetes erecta L.) is one of the most important and commercially cultivated ornamental flower crop belonging to the family Asteraceae. It occupies a prominent position in floriculture owing to its attractive flower colour, wide adaptability, ease of cultivation and prolonged flowering period. Marigold is extensively grown throughout India for loose flower production, garland making, religious offerings, landscaping and decorative purposes. Due to its excellent keeping quality and higher productivity, it has become one of the most preferred flower crops among commercial growers. Apart from ornamental value, marigold also possesses considerable medicinal and industrial importance. The flowers are rich in carotenoid pigments, particularly xanthophylls, which are extensively used in poultry feed, food colouring and pharmaceutical industries. The essential oils extracted from marigold flowers exhibit antimicrobial, antifungal and nematicidal properties. Because of these diverse uses, the demand for quality marigold flowers has increased considerably in recent years. Growth, flowering and yield of ornamental crops are greatly influenced by environmental conditions, nutrient management and endogenous hormonal balance within the plant system. Among these factors, plant growth regulators (PGRs) play a significant role in regulating various physiological and biochemical processes associated with plant growth and development. Plant growth regulators are known to influence cell division, cell elongation, flowering behaviour, photosynthesis, assimilate translocation and sink-source relationship in plants. Gibberellic acid (GA₃) is one of the most important growth-promoting hormones which stimulatescell division, stem elongation and flowering in many ornamental crops. It enhances vegetative growth and improves flower quality through increased metabolic activities and mobilization of nutrients. Naphthalene acetic acid (NAA), a synthetic auxin, plays an important role in promoting vegetative growth, root development, flower retention and fruit setting. Ethrel (ethephon), an ethylene-releasing compound, regulates flowering, senescence and various physiological activities in plants. [3,4,9,6] . Similar beneficial responses of GA [2,14,1] . In recent years, commercial cultivation of marigold has expanded rapidly due to increasing market demand for flowers in social, cultural and religious functions. Therefore, enhancement of flower yield and quality through scientific crop management practices has become essential. However, limited information is available regarding the optimum concentration of plant growth regulators under agro-climatic conditions of Agra region. Hence, the present investigation was undertaken to evaluate the effect of different plant growth regulators on growth, flowering and yield attributes of (Tagetes erecta L.).

Materials and Methods

The present investigation was carried out at the Research Farm, Department of Horticulture Raja Balwant Singh College, Bichpuri, Agra (U.P.) during the winter season of 2023-24. The experimental site is situated at 27.20° N latitude and 78.50° E longitude with an elevation of 168 m above mean sea level. The climate of the region is subtropical in nature, characterized by hot summers and cold winters.

The experiment was laid out in Randomized Block Design (RBD) with three replications and ten treatments. The treatments comprised T₀ (Control-water spray), T₁ (GA₃ 50 ppm), T₂ (GA₃ 100 ppm), T₃ (GA₃ 150 ppm), T₄ (NAA 50 ppm), T₅ (NAA 100 ppm), T₆ (NAA 150 ppm), T₇ (Ethrel 50 ppm), T₈ (Ethrel 100 ppm) and T₉ (Ethrel 150 ppm).

Healthy and uniform seedlings of marigold about 4 weeks old were transplanted in well-prepared plots at recommended spacing 30 cm x 45 cm. All the recommended cultural and plant protection practices were followed uniformly for all treatments throughout the crop period. Foliar application of plant growth regulators was carried out at 30 days after appropriate growth stages using a hand sprayer during morning hours.

Observations were recorded on important vegetative, flowering and yield parameters such as plant height (cm), number of branches per plant, days taken to first flower bud appearance, days taken to opening of first flower, length of flower stalk (cm), weight of flower (g), flower diameter (cm), number of flowers per plant, flower yield per plant (g) and flower yield per hectare (q). The recorded data were subjected to statistical analysis as per the method suggested by Panse and Sukhatme (1978). The significance of treatment effects was tested at 5 per cent level of significance.

Results and Discussion

Effect on growth and flowering parameters

The data presented in Table 1 clearly revealed that different plant growth regulators exerted significant influence on vegetative growth and flowering parameters of marigold.

Considerable variation among the treatments was observed for plant height, number of branches, days taken to flower bud initiation, days taken to opening of first flower and flower stalk length. Among all the treatments, foliar application of GA₃ @ 100 ppm proved superior over other treatments for most of the growth and flowering characters. Maximum plant height (62. [4,9,6,5,13,12] . Minimum days taken to first flower bud appearance (36.6 days) and opening of first flower (37.6 days) were recorded under GA 3 100 ppm treatment, which was found significantly superior to all other treatments. However, maximum days were recorded in control in this respect.

Early flowering under gibberellic acid treatment might be due to enhanced physiological activities, accelerated metabolic processes and early differentiation of floral primordia. GA 3 is known to influence endogenous hormonal balance and stimulate synthesis of flowering-related enzymes and proteins which promote early floral initiation. Enhanced translocation of carbohydrates from source to sink tissues might also have contributed towards early flowering. [4,9,6,7] .

Effect on flower yield and quality parameters

The data presented in Table 2 indicated that different plant growth regulators significantly influenced flower quality and yield attributes of marigold. Significant variation among treatments was observed with respect to flower weight, flower diameter, number of flowers per plant, flower yield per plant and flower yield per hectare. Among all the treatments, GA₃ 100 ppm recorded significantly maximum flower weight (9.3 g), flower diameter (7.9 cm), number of flowers per plant (41.7), flower yield per plant (331.8 g) and flower yield per hectare (148.8 q) followed by application of 150ppm NAA. However, statistically minimum values were recorded in control with this respect. The improvement in flower quality and yield parameters under GA₃ treatment may be attributed to enhanced vegetative growth, increased photosynthetic activity and better translocation of assimilates towards reproductive organs. The increase in flower weight and flower diameter under GA 3 application might be due to enhanced cell enlargement and accumulation of carbohydrates in floral tissues. Gibberellic acid possibly stimulated synthesis of proteins, nucleic acids and growth-promoting enzymes which enhanced flower development and quality. Increased flower diameter under GA 3 treatment might also be associated with improved uptake and utilization of nutrients by the plant system. Similar findings were reported by [14,2,4,9,16] . Maximum number of flowers per plant recorded under GA 3 100 ppm treatment may be due to vigorous vegetative growth, production of more branches and increased flower initiation. Better source-sink relationship and enhanced synthesis of photosynthates under GA 3 treatment might have contributed towards increased flower production. Production of higher number of branches under GA 3 treatment provided more flowering sites which ultimately resulted in higher number of flowers per plant. Similar observations were also reported by Kumar et [3,5,6,1,17] . Higher flower yield per plant and per hectare observed under GA 3 100 ppm treatment may be attributed to cumulative effects of increased flower size, higher flower weight and greater number of flowers per plant. Gibberellic acid possibly enhanced photosynthetic efficiency and mobilization of assimilates towards reproductive tissues, thereby improving overall flower production. Enhanced nutrient uptake and improved metabolic activities under GA 3 treatment may also have contributed towards higher flower yield. Similar beneficial effects of GA

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