Effect of the photoperiod response on growth and physiological traits in cut chrysanthemum

Introduction

Chrysanthemum (Chrysanthemum morifolium Ramat.), a member of the Asteraceae family (2n = 36), ranks as one of the world's most important ornamental crops Popularly called the Under natural cycles, Chrysanthemums exhibit vegetative growth during extended summer daylight, while reduced day length in late summer to early autumn triggers bud initiation and flowering (Prasad and Kumar, 2005) [24] . The present investigation was therefore undertaken to evaluate cut Chrysanthemum varieties planted across different months for their photoperiodic response with respect to growth and physiological parameters under open field conditions in the Northern Dry Zone of Karnataka.

Material and Methods

A field experiment was conducted during 2024-25 at the research block of the Department of Floriculture and Landscape Architecture, College of Horticulture, University of Horticultural Sciences, Bagalkot, Karnataka, India. The experimental site experienced maximum monthly rainfall in October (109.7 mm) followed by August (89.9 mm). The mean minimum temperature ranged from 17.72°C to 21.18°C, with relative humidity fluctuating from 23.00 to 86.90 per cent. The soil was prepared by thorough ploughing up to 30 cm depth followed by harrowing and raised beds of 30 cm height, 80 cm width and 30 m length were formed with 45 cm pathways between beds. The experiment was laid out in a Factorial Randomized Complete Block Design (FRCBD) with 25 treatment combinations and two replications, comprising five Chrysanthemum varieties (Champagne Yellow, Artic Queen White, Lollipop Pink, Bright Orange and Bright White) and five planting months (August, September, October, November and December). Rooted cuttings (25-30 days old) were transplanted from August to December 2024 at a spacing of 45 cm × 30 cm, accommodating 40 plants per treatment. Standard plant protection measures were followed to control pests and diseases using appropriate chemical and biological agents. Pinching was carried out at 30 and 45 days after planting to promote lateral branching, and staking was done using bamboo stakes and jute twine to support plant growth. Flowers were harvested at full bloom stage using sharp tools. Observations were recorded on five randomly selected and tagged plants from each treatment in both replications. Growth parameters such as plant height, plant spread, stem girth, number of primary branches and internodal length were measured at 30, 60, 90 and 120 days after transplanting. Physiological parameters including leaf area and leaf area index were recorded at 70 days after planting, while crop growth rate (CGR) and relative growth rate (RGR) were computed using dry matter accumulation at 45 and 75 days after planting. The data obtained were subjected to statistical analysis using the critical difference (CD) at 5 per cent level of significance.

Results and Discussion

The experimental results obtained from the evaluation of cut Chrysanthemum varieties for photoperiodic response under open conditions in the Northern Dry Zone of Karnataka during 2024-25 are presented and discussed below.

Growth Parameters

Plant performance in terms of growth was significantly and directly affected by day length and the intensity of light received. Planting Chrysanthemum during different months led to marked variations in vegetative growth parameters at 30, 60, 90 and 120 DAT. These differences can be attributed to variation in photoperiod across planting months, which created distinct environmental conditions influencing vegetative development.

Plant height differed significantly among varieties at all growth stages, indicating strong genetic control over vegetative growth. The data at 30 and 60 DAT are presented in [20] . Bright White recorded minimum height due to its compact growth habit and restricted internodal elongation, in line with Thiripurasundari et al. (2021) [44] . Similar varietal differences in plant height have been reported by Swaroop et al. (2008) [41] and Banerji et al. (2012) [3] . Different months of planting significantly influenced plant height at all stages. August planting (M₁) produced the tallest plants 22.43, 46.02, 57.17 and 71.92 cm at 30, 60, 90 and 120 DAT which may be attributed to higher light intensity and longer photoperiod that enhanced photosynthetic activity and metabolic processes (Bose et al., 2003; Bhattacharjee and De, 2003; Kumar et al., 2011) [5,6,14] . December planting (M₅) produced the shortest plants (13.49, 27.89, 42.15 and 45.19 cm), attributable to reduced sunshine hours and lower temperatures suppressing vegetative growth (Jose et al., 2017) [11] . The interaction between varieties and months was significant at all stages. M₁V₄ (August × Bright Orange) recorded maximum plant height with 24.10, 50. [20] [1] . [25] . Artic Queen White (V₂) also showed comparatively higher spread (8.01, 14.09, 20.42 and 26.14 cm), indicating inherent vegetative vigour (Singh et al., 2019) [37] . Bright White (V₅) recorded the least plant spread (7.31, 12.98, 19.34 and 24.80 cm), possibly due to compact growth habit and limited lateral branching ability. August planting (M₁) produced the greatest plant spread (9.67, 16.55, 25.13 and 31.65 cm) due to favourable temperature and higher light availability enhancing photosynthetic activity (Singh and Arora, 2009) [35] . December planting (M₅) produced the minimum spread (5.63, 10.73, 15.80 and 19.46 cm) due to reduced sunshine hours and lower temperatures (Khan and Qureshi, 2017) [12] .

The . [35] . A progressive reduction was observed with delayed planting, reaching the minimum in December (M₅) at 6.35, 11.46, [2,34] .

Number of primary branches

Marked differences in primary branch number were observed among varieties, reflecting the influence of genetic makeup on branching behaviour. Bright Orange (V₄) produced the highest number of primary branches (5.37, 6.56 and 7.69 at 60, 90 and 120 DAT), attributed to vigorous vegetative growth and greater lateral shoot development, followed by Artic Queen White (V₂) with 4.86, 6.06 and 6.90 (Kumar et al., 2016) [16] . [33,49] . The M₁V₄ combination consistently produced the highest primary branch count (7.92, 9.42 and 11.67 at 60, 90 and 120 DAT), while M₅V₅ recorded the lowest (2.02, 2.33 and 3.56), attributable to the combined influence of a less vigorous genotype and unfavourable winter conditions (Aashutosh et al., 2019; Allard and Bradshaw, 1964) [1] .

Stem girth differed significantly among varieties at all growth stages. Bright Orange (V₄) recorded maximum stem girth of 0.60, 0.82, 1.15 and 1.31 cm at 30, 60, 90 and 120 DAT, reflecting superior vigour and effective channelling of dry matter into structural biomass, likely associated with rapid cambial cell division and superior vascular bundle arrangement (Eisa et al., 2022) [8] . Artic Queen White (V₂) followed with 0.53, 0.78, 1.07 and 1.22 cm, while Bright White (V₅) recorded the minimum (0.43, 0.63, 0.93 and 1.06cm). August planting (M₁) produced the thickest stems (0.62, 0.84, 1.16 and 1.33 cm) due to favourable thermo-photoperiodic conditions that enhanced photosynthesis and carbohydrate accumulation (Sajid, 2025; Sadhna, 2025) [30] . Late-season December planting (M₅) recorded the minimum (0.41, 0.63, 0.93 and 1.05 cm) due to reduced light intensity and sub optimal temperatures (Van der Ploeg and Heuvelink, 2020) [45] .

The M₁V₄ treatment recorded maximum stem girth (0.81, 0.96, 1.38 and 1.54 cm), while M₅V₅ recorded the lowest (0.29, 0.41, 0.74 and 0.78 cm), demonstrating how harsh low-light winter conditions can further stunt a variety already possessing low growth vigour. This synergistic relationship is supported by Kumari et al. (2023) [17] and Sadhna (2025) [21,36] . Artic Queen White (V₂) followed with 1.91, 2.15, 2.42 and 2.77 cm, while Bright White (V₅) showed the minimum (1.75, 2.00, 2.24 and 2.51 cm).

August planting (M₁) yielded significantly longer internodes (1.98, 2.24, 2.52 and 2.83 cm) due to the ideal thermophotoperiodic window with extended daylight and favourable temperatures facilitating rapid cell expansion, boosting photosynthetic rate and carbohydrate reserves essential for stem stretching (Sajid, 2025) [30] . December planting (M₅) resulted in the shortest internodes (1.74, 2.00, 2.25 and 2.54 cm), likely due to inhibition of auxin and gibberellin synthesis under short-day and low-temperature conditions (Van der Ploeg and Heuvelink, 2020) [45] .

The [17] , these results demonstrate that while a variety's genetics provides the blueprint for growth, the planting month provides the energy needed to realise that potential. [4,10] . Artic Queen White (V₂) followed with 2067.73 cm², while Bright White (V₅) recorded the minimum (1788.55 cm²), reflecting its inherent tendency towards compact growth. August planting (M₁) produced the largest leaf area (2229.21 cm²) as the long days and warm weather provided the perfect mix for leaf expansion before flowering initiation (Singh and Arora, 2009) [35] . Later planting months showed progressive reductions September (M₂) at 2080.95 cm² and December (M₅) at 1887.52 cm² as colder, shorter days slowed metabolism and prevented full leaf expansion (Sujatha et al., 2023) [39] . The M₁V₄ interaction combination displayed the maximum leaf area (2673.68 cm²), followed by M₁V₂ (2335.13 cm²), confirming that a vigorous variety performs best under favourable environmental conditions (Wilkins and Dodson, 1985) [47] . The minimum was recorded in M₅V₅ (1621.63 cm²), as a less vigorous variety was exposed to unfavourable winter conditions (Khan and Qureshi, 2017; Srivastava et al., 2022) [12,38] .

Leaf Area Index (LAI) Significant variation in LAI was observed among varieties. Bright Orange (V₄) recorded the maximum LAI of 1.62, indicating its natural superiority in building a thick canopy that captures more sunlight, followed by Artic Queen White (V₂) with 1.54 (Beniwal et al., 2021) [4] . Bright White (V₅) recorded the least LAI (1.35), reflecting its compact plant architecture (Sujatha et al., 2023) [39] . August planting (M₁) yielded the maximum LAI (1.72) as the planting date gave adequate good-weather days for leaf development before flowering (Singh and Arora, 2009) [35] . December planting (M₅) showed the lowest LAI (1.30), as shorter days and colder weather signalled the plant to slow down leaf growth. The M₁V₄ combination achieved the maximum LAI of 1.96, followed by M₁V₂ with 1.76 (Wilkins and Dodson, 1985) [47] . The M₅V₅ combination recorded the minimum LAI of 1.04, demonstrating how a less vigorous variety is further constrained by poor winter growing conditions (Khan and Qureshi, 2017) [12] . [50] . December planting (M₅) showed the lowest CGR (6.94 g m⁻² day⁻¹) due to reduced day length and lower temperatures limiting photosynthesis.

Crop

The M₁V₄ treatment reached a maximum CGR of 10.01 g m⁻² day⁻¹, demonstrating that the genetic potential of a variety is only fully unlocked when synchronised with the ideal environment (Swaroop et al., 2025) [42] . Conversely, M₅V₅ recorded the minimum (5.14 g m⁻² day⁻¹), illustrating a double-stress scenario where low varietal vigour was further inhibited by sub-optimal December conditions (Zhou et al., 2025) [25] . [46] . Artic Queen White (V₂) followed with 1.78 g g⁻¹ × 10⁻², while Bright White (V₅) recorded the minimum RGR (1.24 g g⁻¹ × 10⁻²), suggesting a slower internal growth mechanism and lower assimilation efficiency (Mishra et al., 2025) [19] .

August planting (M₁) recorded the highest growth efficiency (1.67 g g⁻¹ × 10⁻²), attributable to favourable climatic conditions during late summer that supported sustained plant growth through accumulation of additional heat units (Prakash and Fatmi, 2023) [23] . December planting (M₅) showed the lowest efficiency (1.48 g g⁻¹ × 10⁻²), as low winter temperatures reduced nutrient movement within plants and limited biomass accumulation relative to plant size (Thakur, 2022) [43] . The M₁V₄ combination was the most efficient, recording a peak RGR of 1.96 g g⁻¹ × 10⁻², confirming that matching a fast-growing variety with optimal seasonal conditions further amplifies growth efficiency (Reddy and Gupta, 2025) [28] . The M₅V₅ treatment recorded the minimum RGR (1.05 g g⁻¹ × 10⁻²), demonstrating that a naturally slower variety is further constrained by the short, cold days of winter (Sharma et al., 2018) [34] .

Conclusion

The present investigation clearly demonstrates that both varietal selection and planting time are critical factors influencing the growth and physiological performance of cut Chrysanthemum under open field conditions in the Northern Dry Zone of Karnataka. Among the varieties evaluated, Bright Orange (V₄) exhibited superior performance across all growth parameters, including plant height, plant spread, number of primary branches, stem girth and internodal length, as well as physiological traits such as leaf area, leaf area index, crop growth rate and relative growth rate, which may be attributed to its strong genetic potential, higher photosynthetic efficiency and better assimilate translocation.

With respect to planting time, August (M₁) was found to be the most favourable, promoting maximum vegetative growth and physiological efficiency due to optimal photoperiod, temperature and moisture conditions, whereas December (M₅) resulted in the poorest performance owing to unfavourable low temperature and short-day conditions. The interaction effect further revealed that the combination of August planting with Bright Orange (M₁V₄) produced the highest values for all observed traits, indicating that the full potential of a variety is realized only under suitable environmental conditions, while December planting with Bright White (M₅V₅) recorded the lowest performance.

Overall, the study highlights the importance of genotype × environment interaction in Chrysanthemum cultivation and recommends planting Bright Orange in August to achieve enhanced growth, physiological efficiency and overall crop vigour in this agro-climatic region, while suggesting further research on flowering, yield and economic aspects for comprehensive recommendations.

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