Assessment of genetic variability and diversity in Niger (Guizotia abyssinica (L.f.) Cass)

Introduction

Niger (Guizotia abyssinica (L.f.) Cass.) is an important minor oilseed crop belonging to the family Asteraceae. It is a highly cross-pollinated annual diploid species (2n = 2x = 30) cultivated primarily for its seeds and oil. Although the crop originated in the Ethiopian highlands of tropical Africa, India is recognized as its secondary centre of diversity and has become the world's largest producer and exporter of niger seed. At present, niger is cultivated over an area of approximately 85,000 ha in India, with an annual production of 28,000 metric tonnes and an average productivity of 329 kg ha⁻¹. In Maharashtra, the crop occupies about 3.94 thousand ha with a production of 1,100 metric tonnes and an average productivity of 279 kg ha⁻¹, which is lower than the national average. Indian niger seed is exported mainly to the United States, the Netherlands, Italy, Germany, Belgium and Spain, and its export value has increased remarkably from ₹12 crore during 1990-91 to ₹281.95 crore during 2023-24, reflecting its growing economic importance. Niger seeds contain 32-40% oil, characterized by a high proportion of unsaturated fatty acids. The oil contains approximately 75-80% linoleic acid, 5-8% oleic acid, and 7-8% palmitic and stearic acids, while Indian genotypes generally possess about 55% linoleic acid and 25% oleic acid. The seeds contain approximately 19.4% protein, 0.05% calcium and 0.18% phosphorus, whereas the defatted meal contains about 30% protein and 23% crude fibre, making it a valuable livestock feed. The high linoleic acid content, along with naturally occurring tocopherols and sterols, enhances the nutritional quality of niger oil and contributes to its health-promoting properties, including protection against cardiovascular diseases. The oil is also utilized in food, cosmetic and paint industries, while the absence of pesticide residues further enhances its export potential. Despite its nutritional, industrial and economic significance, niger has remained a neglected oilseed crop with limited systematic breeding efforts. Low productivity is mainly attributed to cultivation under rainfed and marginal environments, the use of traditional low-yielding cultivars, protandrous selfincompatibility, poor seed set, dependence on insectmediated cross-pollination, and susceptibility to various biotic stresses. Consequently, the available genetic variability has not been adequately exploited for crop improvement. Comprehensive evaluation of germplasm for genetic variability, genetic diversity, heritability and associated yield-contributing traits is therefore essential for identifying superior genotypes and developing efficient breeding strategies. The present investigation was undertaken to assess the genetic potential of diverse niger genotypes and generate information useful for the selection of promising parents and the development of high-yielding cultivars with improved agronomic performance and enhanced seed yield.

Material and Methods

The investigation of 35 genotypes which were obtained from the ZARS, Igatpuri, Nashik. The experiment was evaluated in a Randomized Block Design (RBD) with two replications each genotype was sown in single row of 4.5 m length with spacing 30 cm between row and 15 cm within rows. The observations were recorded on five randomly selected plants from each treatment in each replication for ten morphological characters viz., days to 50 per cent flowering, days to maturity, plant height, number of branches per plant, number of internodes per plant, number of capitula per plant, number of seeds per capitulum, 1000seed weight, seed yield per plant, and oil content. Analysis of variance commonly applicable to the Randomized Block Design (Panse and Sukhatme, 1995) [25] . The analysis of divergence was carried out by D 2 statistics proposed by Mahalanobis (1936) as described by Rao (1952) [33] .

Results and Discussion

Analysis of Variances

The analysis of variance revealed highly significant differences for all the characters studied except for number of branches per plant and internodes per plant (Table 1). In plant breeding programme, wide range of variation among the genotypes paves the way to bring in desirable improvement in the crop. The present material therefore, could serve a pool for selection of suitable material in the breeding programme. Similar results were also reported by Patil (2000) [30] , Kenjale et al. (2003) [16] , and Sreedhar (2003) [38] .

Genetic variability parameters

Parameters of genetic variability were recorded on ten quantitative traits viz., days to 50% flowering, days to maturity, plant height, number of branches per plant, number of internodes per plant, number of capitula per plant, number of seeds per capitula, 1000 seed weight, seed yield per plant and oil content.

Genotypic and Phenotypic Coefficients of Variation

Estimates of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were classified as suggested by Sivasubramanian and Madhavamenon (1973) and are presented in Table 2. The characters of Number of branches per plant recorded high estimates of GCV (21.83%). Moderate GCV were observed for Days to 50 per cent flowering (10.59%), Seed yield per plant (12.39), 1000 seed weight (15.27%), Number of internodes per plant (18.06%). While Low GCV were observed for Oil content (%) (4.99%) High estimates of PCV were observed for Number of branches per plant (22.29), followed by 1000 seed weight (20.49). Medium estimates of PCV were observed for Days to 50 per cent flowering (10.59), Seed yield per plant (17.81), Number of internodes per plant (18.99). While, low estimates of PCV were observed for Oil content (%) (5.37) This was in conformity with the results of Ahmad et al. (2003) [1] , Sreedhar (2003) [38] , Patil and Duhoon (2005) [31] , Panda and Sial (2012) [34] , Ahmad et al (2016) [2] , Dudhe et al. (2017) [11] , Kusumlata et al (2018), Fekadu (2020) [12] , Gururaja et al. (2021) [14] , Bhoite et al. (2023) [6] and Baghel et al (2018) [4] . . Heritability Estimates of heritability in broad sense is presented in Table 2. The high estimates of heritability in broad sense were observed for Plant height (98.60%) followed by Number of capitula per plant (98.10%), Days to 50 per cent flowering (97.20%), Days to maturity (96.50%), Number of branches per plant (95.90%) and Number of seeds/capitula (94.70%), Number of internodes per plant (90.40%), Oil content (%) (86.60%). Whereas low estimates of heritability were observed for Seed yield per plant (48.40%), and 1000 seed weight (55.5%). While high heritability coupled with high genetic advance as % of mean was observed for Days to 50% flowering, number of branches per plant, number of internodes per plant, indicating the predominant role of additive gene action in the inheritance of these characters. These results are in conformity with results of Mathur and Gupta (1993) [20] , Borole and Patil (1997) [8] , Patil (2000) [30] , Kenjale et. al. (2003) [16] , Sreedhar (2003) [38] , Ahmad et. al. (2003) [1] and Patil and Duhoon (2005) [31] , Patil et al. (2013) [28] , Ekhlaque et al. (2016), Bamrotiya et al. (2016) [5] , Kumar and Bisen (2016) [17] , Valli et al. (2016) [42] , Teja et al. (2024) [18] .

Genetic advance

Genetic advance (at 5% selection intensity) was calculated by the formula cited by Allard (1960) [3] . The range of genetic advance observed from 0.64 to 25.31. The highest estimate of GA for Plant height was 25.31, followed by number of capitula per plant (20.33). Days to 50 per cent flowering (14. The range of genetic advance as a percent of mean is classified as suggested Johanson, et al. (1955a). High estimates of genetic advance as per cent of mean (Table 2) was observed for Number of branches per plant (44.03%) followed by Number of internodes per plant (35.38%), 1000 seed weight (23.45%), Days to 50 per cent flowering (21.21%).The medium estimates of genetic advance as per percent of mean was observed for Number of seeds per capitula (19.43%), Number of capitula per plant (18.04%), Seed yield per plant (17.77%), plant height (15.08%), days to maturity (14.70%) and Low estimates of genetic advance as percent of mean were observed for Oil content (%) (9.57%). Considering the estimates of genotypic coefficient of variation, heritability, and genetic advance as per cent of mean together, it is evident that days to 50 per cent flowering, number of branches per plant, and number of internodes per plant are the most important traits. Therefore, hybridization followed by selection in the early generations for these characters would be an effective approach for their genetic improvement in niger.

Genetic divergence

The Mahalanobis D² statistics are computed for all possible pair of thirty five genotypes in order to assess the genetic diversity present among the genotypes under study. The clustering pattern based on magnitude of D² values was made and are presented in Table 5. The thirty-five genotypes are grouped into eight clusters. It reveals from Table 3 that cluster II had maximum eight genotypes followed by cluster I and III seven genotypes. The cluster VI have five genotypes followed by cluster IV and VII with three genotypes. The cluster V, VIII were solitary since they had only one genotype. Similar findings, where two of the five clusters were mono-genotypic, were reported by Aboye B.M. (2021). The average inter and intra-cluster D² distances are presented in Table 4. The inter-cluster distance ranged from 28.62 to 216.34. The maximum inter-cluster distance was observed between clusters I and V (D² = 216.34), followed by clusters I and IV (D² = 199.77) and clusters III and V (D² = 187.61). In contrast, the minimum inter-cluster distance was recorded between clusters IV and V (D² = 28.62), followed by clusters VI and VIII (D² = 38.02) and clusters II and III (D² = 41.87).The intra-cluster distance ranged from 0.00 to 24.00. Among all the clusters, cluster VI exhibited the highest intra-cluster distance (D² = 24.00), followed by cluster IV (D² = 21.55) and cluster VII (D² = 17.72). The cluster means for all ten characters are presented in Table 5. Considerable inter-cluster variation was observed for days to 50 per cent flowering, days to maturity, plant height, number of branches per plant, number of capitula per plant, number of internodes per plant, number of seeds per capitula, seed yield per plant, 1000 seed weight, and oil content. The cluster mean for days to 50 per cent flowering ranged from 56.20 (cluster V) to 78.77 (cluster I). Similarly, the cluster mean for days to maturity varied from 87.44 (cluster V) to 109.71 (cluster I). The cluster mean for plant height ranged from 159.91 cm (cluster III) to 198.96 cm (cluster V), while the cluster mean for number of branches per plant varied from 9.60 (cluster I) to 17.70 (cluster IV). The cluster mean for number of internodes per plant ranged from 9.94 (cluster I) to 15.98 (cluster V). The cluster mean for number of capitula per plant ranged from 65.75 (cluster I) to 98.44 (cluster VII). The cluster mean for number of seeds per capitula ranged from 14.39 (cluster I) to 20.14 (cluster II). The cluster mean for 1000 seed weight varied from 2.49 (cluster I) to 4.07 (cluster V). Similarly, the cluster mean for seed yield per plant ranged from 2.67 (cluster I) to 6.83 (cluster IV), whereas the cluster mean for oil content ranged from 36.79 (clusters V and VIII) to 41.74 (cluster I). Similar findings have been reported by Chatterjee (1983) [9] , Sohan (1987) [37] , Mehta (1989) [21] , Chatterjee et al. (1991) [10] , Jagadev and Samal (1991) [15] , Biswas et al. (1993) [17] , Ravanappa et al. (1994), Kumar (1999) [34] , Sreedhar et al. (2006) [39] , Parameshwarappa et al. (2009, 2011) [26,27] , Sangita et al. (2012), Goyal and Bisen (2017) [13] , Misganaw (2017) [22] , Naik et al. (2018) [23] , Suryanarayana et al. (2018b) [40] , and Suryanarayana et al. (2019) [41] .

Conclusion

The present investigation revealed substantial genetic variability among the thirty-five niger genotypes, as indicated by significant differences for all characters except number of branches per plant and number of internodes per plant. The estimates of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) indicated the presence of adequate variability for important quantitative traits, providing scope for effective selection. High heritability coupled with high genetic advance as per cent of mean for days to 50 per cent flowering, number of branches per plant, and number of internodes per plant suggested the predominance of additive gene action and the effectiveness of selection for their improvement.

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