Genetic variability studies in F5 population of China aster [Callistephus chinensis (L.) Nees]

Introduction

China aster (Callistephus chinensis (L.) Nees.) is an important ornamental flowering crop belonging to the family Asteraceae and is widely cultivated for loose flowers, cut flowers and ornamental purposes. It is valued for its wide range of flower colours and forms and is extensively used for interior decoration, floral arrangements and garden display (Munikrishnappa et al., 2013, Bhargav et al., 2016) [10,3] . Among traditional ornamental flowers, China aster occupies a prominent position next only to marigold and chrysanthemum. The crop is cultivated commercially in several countries across the world. In India, China aster is grown extensively in states such as Karnataka, Tamil Nadu, Telangana, Andhra Pradesh, Maharashtra and West Bengal, covering an estimated area of about 3,500 ha. Karnataka is one of the major producing states, with approximately 207 ha under cultivation and a production of about 1,448 metric tonnes, recording a productivity of 7.01 t ha⁻¹ (Anonymous, 2020) [1] . Favourable climatic conditions in regions like Bengaluru support year-round cultivation, thereby enhancing its commercial importance. Despite its economic significance, considerable variation exists in yield and flower quality among China aster genotypes. Genetic improvement of the crop largely depends on the availability and effective utilization of genetic variability for yield and its component traits. The magnitude of genetic variability present among genotypes determines the efficiency of selection and the scope for developing superior cultivars. Genetic variability is generally higher in early generations due to diverse genetic combinations but tends to decline in later generations due to selection and stabilization of desirable traits. Phenotypic expression of quantitative traits is influenced by both genetic and environmental factors. Therefore, estimation of phenotypic and genotypic coefficients of variation, heritability and genetic advance is essential for assessing heritable variability and predicting the response to selection, thereby providing a scientific basis for genetic improvement in China aster.

Materials and Methods

The present investigation was carried out in the Department of Floriculture and Landscape Architecture, College of Horticulture, Bagalkot, Karnataka during rabi season of 2024-25 period. The plant material comprised F 5 progenies derived from four hybrid combinations: Miraj Local × AAC-1, Namdhari White × Arka Kamini, AAC-1 × Arka Poornima and Arka Poornima × AAC-1. The respective parental lines, AAC-1, Miraj Local, Namdhari White, Arka Poornima and Arka Kamini, were included as checks. These F 5 populations were developed through selfing of F 4 hybrid lines, resulting in a total of 37 genotypes, including 32 F 5 lines and five parental lines. The experiment was laid out in a randomized complete block design with two replications. Seedlings were transplanted at 30 × 30 cm spacing using the raised bed method and recommended agronomic practices were followed. Observations were recorded for growth, flowering, yield and quality traits. Genetic variability was assessed using mean, range, phenotypic and genotypic coefficients of variation (PCV and GCV), while broad-sense heritability and genetic advance were calculated to determine the heritable component of variation and potential for selection of superior genotypes (Burton and DeVane, 1953) [4] .

Results and Discussion

The estimates of phenotypic coefficient of variation (PCV) were consistently higher than the corresponding genotypic coefficient of variation (GCV) for all the characters studied (Table 2), indicating the influence of environmental factors on the expression of these traits. High PCV and GCV values were recorded for number of branches (23.30% and 21.19%, respectively) and shelf life (26.93% and 25.23%, respectively). These findings are in agreement with Sagar et al. (2024) [13] in China aster and Gurung et al. (2023) [6] in chrysanthemum. This suggests the presence of substantial genetic variability and greater scope for improvement through selection. Moderate PCV and GCV values were observed for plant height (16.03% and 12.56), stem girth (17.61% and 14.16%), days to first flowering (15.33% and 11.04%), days to 50% flowering (12.90% and 11.04%), length of ray florets (16.48% and 12.91%), disc diameter (16.35% and 13.86), flower yield per plant (16.50% and 14.08%) and total yield per hectare (16.30% and 14.21%). Comparable observations were reported by Bhargav et al. (2019) [2] and Tanzeela et al. in China aster. This indicates moderate variability with a reasonable contribution of genetic factors. Moderate PCV and low GCV were observed for flowering duration (10.68% and 8.27%) and no. of flowers / plant (12.45% and 9.58%) suggesting that these traits are strongly influenced by environmental factors, thereby reducing the efficiency of direct phenotypic selection. Results comparable to the present study have been documented by Sagar et al. (2024) [13] and Tanzeela et al.

(2023) in China aster. Conversely, greater variability for number of flowers per plant has been reported by Bhargav et al. (2019) [2] and Ramya et al. (2019) [12] in China aster which could be due to differences in genetic material and prevailing environmental conditions. Low PCV and GCV was observed for flower diameter (9.07% and 6.05%) and vase life (7.84% and 5.71%) suggesting limited variability for these traits. In contrast, higher PCV and GCV values for these traits have been reported by Ramya et al. (2019) [12] in China aster and Devi et al. (2020) [5] in dahlia, possibly due to differences in genetic material and environmental conditions. High heritability coupled with high genetic advance as per cent of mean for number of branches (82.68% and 39.69%), stem girth (61.66% and 23.45%), shelf life (87.78% and 48.70%), length of ray florets (61.33% and 20.82%), disc diameter (71.92% and 24.22%), flower yield per plant (72.77% and 24.33%) and total yield per hectare (76.08% and 25.54%) indicates the predominance of additive gene action, suggesting that direct selection would be effective for improving these traits. Similar associations have been reported earlier in China aster by Bhargav et al. (2019) [2] and Ramya et al. (2019) [12] , in marigold by Tamut and Singh (2019) [14] and Thirulmurugan et al. High heritability coupled with moderate genetic advance for days to 50% flowering (73.26% and 19.47%) and individual flower weight (61.78% and 16.52%) indicates good genetic control, though the expected response to selection would be moderate, as also observed by Nandana (2022) [11] in China aster. Moderate heritability and genetic advance for days to first flowering (57.99% and 18.31%), duration of flowering (59.93% and 13.19%) and no. of flowers / plant (59.18% and 15.18%) indicate the combined influence of genetic and environmental factors. Higher estimates for these traits have been reported earlier in China aster by Bhargav et al. (2019) [2] , in dahlia by Devi et al. (2020) [5] and in chrysanthemum by Kavana et al. (2024) [7] possibly due to differences in genetic material and growing conditions. Vase life (53.12% and 8.58%) and flower diameter (44.42% and 8.30%) exhibited moderate heritability with low genetic advance, indicating limited scope for improvement through direct selection due to environmental influence. Hence, improvement of these traits may require hybridization or improved crop management practices. Similar traits showing higher heritability and genetic advance have been reported earlier in China aster by Khangjarakpam et al. (2014) [8] and Ramya et al. (2019) [12] and in chrysanthemum by Vandana et al. (2024) [17] which may be attributed to differences in genetic material and experimental conditions.

Conclusion

The present investigation revealed the presence of considerable genetic variability among the F₅ populations of China aster for various growth, flowering and yield-related traits. Characters such as number of branches, stem girth, shelf life, length of ray florets, disc diameter, flower yield per plant and total yield per hectare, which exhibited high heritability coupled with high genetic advance, can be effectively exploited through direct selection and utilized for the development of high yielding China aster genotypes in future breeding programmes.

Acknowledgement

AcknowledgeThe authors gratefully acknowledge the Department of Floriculture and Landscaping for providing the necessary facilities to carry out this research.

References

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