Assessment of genetic variability, heritability and genetic advance for yield and its components in safflower (Carthamus tinctorius L.)

Introduction

Safflower (Carthamus tinctorius L.) is an important oilseed crop cultivated for its edible oil and other useful products. Improvement in safflower productivity depends largely on the availability of suitable genetic variation in breeding material. Quantitative characters such as flowering, maturity, plant architecture, yield components and seed yield are influenced by both genetic constitution and environmental conditions. Therefore, estimating the different components of variability is an important step before undertaking effective selection. Genotypic and phenotypic coefficients of variation provide a measure of the extent of variability present in a population. The genotypic coefficient of variation reflects the genetic component of observed variation, whereas the phenotypic coefficient of variation includes both genetic and environmental effects. Comparing these estimates helps in understanding the extent to which environmental conditions influence the expression of individual characters. Heritability provides an estimate of the proportion of phenotypic variation attributable to genetic differences among the genotypes. However, heritability alone does not indicate the expected improvement from selection. Genetic advance and genetic advance as percent of mean provide complementary information about the likely response to selection. A combination of high heritability and high genetic advance as percent of mean is particularly useful for identifying characters in which selection may produce substantial improvement.

In the present investigation, 38 safflower genotypes were evaluated to estimate genotypic and phenotypic variability parameters for yield and yield-attributing traits. The study also considered heritability, genetic advance and genetic advance as percent of mean to obtain a broader understanding of the selection potential of the characters.

Materials and Methods

Experimental material and design

The experimental material consisted of 38 safflower genotypes, including NARI 36 as the check. The trial was conducted at OILSEEDS RESEARCH UNIT, Dr. PDKV, AKOLA during RABI 2025. The genotypes were evaluated in a randomized block design with three replications.

Characters recorded

Data were recorded for days to 50% flowering, days to maturity, plant height (cm), number of primary branches per plant, number of capitula per plant, number of seeds per capitulum, diameter of capsule (cm), hundred seed weight (g), seed yield per plant (g) and oil content (%).

Estimation of variability parameters

Genotypic variance was estimated from the analysis of variance as σ²g = (MSG -MSE)/r, where MSG is the mean square due to genotypes, MSE is the error mean square and r is the number of replications. Phenotypic variance was obtained as σ²p = σ²g + σ²e, where σ²e represents environmental variance. Genotypic coefficient of variation was calculated as GCV = (√σ²g/X ̄) × 100, while phenotypic coefficient of variation was calculated as PCV = (√σ²p/X ̄) × 100. Environmental coefficient of variation was estimated as ECV = (√σ²e/X ̄) × 100. Broad-sense heritability was estimated following Hanson et al. (1956) as h² = (σ²g/σ²p) × 100. Heritability values were classified as low (0-30%), moderate (30-60%) and high (>60%) following Robinson et al. (1951) [8] . Genetic advance was estimated following Johnson et al. (1955) [3] using GA = i h² σp, where i is the selection differential (2.06 at 5% selection intensity), h² is broadsense heritability and σp is the phenotypic standard deviation. Genetic advance as percent of mean was calculated as GAM = (GA/X ̄) × 100. GAM values were classified as low (0-10%), moderate (10-20%) and high (>20%) following Johnson et al. (1955) [3] .

Results and Discussion

Mean performance and variability

The 38 safflower genotypes differed considerably for the characters evaluated. The overall means were 82.05 days for days to 50% flowering, 122.55 days for days to maturity, 87.21 cm for plant height, 17.67 primary branches per plant, 41.16 capitula per plant, 25.64 seeds per capitulum, 2.92 cm for diameter of capsule, 4.91 g for hundred seed weight, 23.65 g for seed yield per plant and 32.29 percent for oil content. The differences among genotypes indicate the presence of exploitable variation for breeding purposes.

Genotypic and phenotypic coefficients of variation

Phenotypic coefficient of variation (PCV) exceeded genotypic coefficient of variation (GCV) for every character studied, indicating that environmental factors contributed to the phenotypic expression of the traits, although the magnitude of environmental influence varied among characters. A higher PCV than GCV for quantitative traits is commonly reported in safflower and indicates the contribution of environmental variation to the total phenotypic variability (Manikya Minnie et al., 2018; Sudha Rani et al., 2020) [4,5] . The largest GCV was recorded for seed yield per plant (29.35%), followed by number of capitula per plant (15.70%), number of branches per plant (13.39%), hundred seed weight (13.18%) and diameter of capsule (12.92%). The corresponding PCV values were 31.17, 18.54, 16.81, 15.12 and 14.67 percent, respectively. The relatively high GCV and PCV observed for these traits indicate the presence of considerable variability and suggest greater scope for their improvement through selection. Similar high variability for seed yield, number of capitula per plant and seed weight has been reported in safflower germplasm (Manikya Minnie et al., 2018; Neelima et al., 2021) [4,6] . In contrast, oil content recorded the lowest GCV (3.16%) and PCV (6.17%), followed by days to maturity with GCV and PCV values of 3.74 and 7.30 percent, respectively, indicating comparatively limited genetic variability for these characters in the material studied. The relatively small difference between GCV and PCV for seed yield per plant suggests that environmental influence on its expression was comparatively lower than for traits showing a wider difference between the two estimates. Consequently, a substantial proportion of the observed variation in seed yield per plant appears to be attributable to genetic differences among the genotypes. Similar observations of comparatively high GCV and PCV for seed yield and yield components have been reported in safflower.

Heritability, genetic advance and genetic advance as percent of mean

Broad-sense heritability varied from 26.30 to 88.65 percent. Seed yield per plant recorded the highest heritability (88.65%), followed by diameter of capsule (77.67%), hundred seed weight (75.91%), number of capitula per plant (71.76%), number of primary branches per plant (63.51%) and number of seeds per capitulum (62.76%). Days to 50% flowering showed moderate heritability (47.09%), whereas days to maturity, plant height and oil content had relatively low estimates. Variation in heritability among safflower traits has also been reported in earlier studies, with high heritability observed for several yield and yield-attributing traits. Genetic advance ranged from 0.69 for diameter of capsule to 13.46 for seed yield per plant. When expressed as a percentage of the mean, the highest genetic advance as percent of mean (GAM) was obtained for seed yield per plant (56.92%). High GAM was also recorded for number of capitula per plant (27.40%), hundred seed weight (23.65%), diameter of capsule (23.46%) and number of primary branches per plant (21.99%). Number of seeds per capitulum had moderate GAM (18.54%), whereas days to 50% flowering, days to maturity, plant height and oil content recorded low GAM values. Similar combinations of high heritability and high genetic advance as percent of mean have been reported for seed yield and several yield components in safflower, suggesting considerable scope for selection of superior genotypes.

The simultaneous occurrence of high heritability and high GAM for seed yield per plant, number of capitula per plant, diameter of capsule, hundred seed weight and number of primary branches per plant indicates substantial genetic variability and greater expected response to selection for these traits. High heritability coupled with high genetic advance is generally considered an indication of the predominance of heritable genetic effects, particularly additive genetic variance, and therefore provides a stronger basis for selection than either heritability or genetic advance considered independently. Among the characters studied, seed yield per plant was particularly promising because it exhibited the highest GCV and PCV together with the highest heritability and GAM. This combination indicates considerable genetic variability, high transmissibility of the observed variation and substantial expected genetic progress through selection. Similar findings have been reported in safflower, where high heritability coupled with high genetic advance was observed for seed yield and important yieldcontributing traits.

Conclusion

The evaluation of 38 safflower genotypes demonstrated appreciable genetic variation for yield and associated characters. Phenotypic coefficients of variation were consistently higher than the corresponding genotypic coefficients, confirming some contribution of environmental effects to trait expression. Seed yield per plant showed the most favourable variability profile, with high GCV (29.35%), PCV (31.17%), broad-sense heritability (88.65%) and GAM (56.92%). Number of capitula per plant, hundred seed weight, diameter of capsule and number of primary branches per plant also showed high heritability together with high GAM. These traits therefore appear promising for selection and can be given emphasis in breeding programmes aimed at improving safflower productivity.

References

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