Harnessing double cross populations to generate genetic variability for yield improvement in linseed

Introduction

Linseed (Linum usitatissimum L.) is an important industrial oilseed crop cultivated worldwide for its high-quality oil rich in Alpha-Linolenic Acid (ALA) and its diverse applications in food, pharmaceutical, cosmetic and fiber industries (Kumar et al., 2018) [11] . Despite its economic significance, genetic improvement for seed yield and related agronomic traits has been relatively slow due to the narrow genetic base of cultivated germplasm and the complex inheritance of quantitative traits (Dhirhi et al., 2018; Mahto & Mishra, 2025) [3,14] . Genetic variability provides the fundamental basis for crop improvement by enabling effective selection of superior genotypes with desirable combinations of agronomic traits (Kaur et al., 2024; Mohammad et al., 2022) [10,18] . Conventional biparental crosses, although widely employed in linseed breeding, involve only two parental genomes and often produce limited allelic recombination, thereby restricting the probability of recovering transgressive segregants for complex traits like seed yield, capsule number and seed weight (Kumar et al., 2017; Markandey et al., 2022) [13,17] . Double cross breeding offers an effective approach to expand the genetic base by combining favourable alleles from four genetically diverse parents into a single segregating population (Mahto et al., 2019; Mahto et al., 2020) [15,16] . This multi-parent mating design increases opportunities for genetic recombination, enhances allelic diversity and facilitates the accumulation of favourable gene combinations governing quantitative traits (Chaudhari et al., 2025) [2] . The greater recombination achieved through double crosses promotes transgressive segregation and increases the likelihood of identifying elite recombinants with improved yield potential and desirable agronomic performance (Mohammad et al., 2022; Sahu et al., 2022) [18,23] . Furthermore, the use of genetically divergent parents minimizes the limitations associated with narrow genetic diversity and enhances breeding efficiency by generating populations with wider phenotypic and genotypic variations (Hoque et al., 2020; Kumar et al., 2021) [7,12] . The effectiveness of selection largely depends on the magnitude of genetic variability, heritability and expected genetic advance present within breeding populations. Traits exhibiting high genetic variability coupled with high heritability and substantial genetic advance are generally governed by additive gene action and respond efficiently to selection (Abtahi et al., 2022; Kaur et al., 2024; Paul et al., 2017) [1,10,20] . Therefore, assessment of variability parameters in double cross-derived populations is essential for identifying promising recombinants and formulating effective breeding strategies for yield improvement. Although double cross breeding has been recognized as a valuable approach for enhancing recombination, limited information is available regarding the extent of genetic variability generated in such populations of linseed. Therefore, the present investigation was undertaken to evaluate the genetic variability, heritability and genetic advance in double cross-derived populations of linseed.

Materials and Methods

Plant material and development of double cross population

The experimental material comprised a double cross-derived population (Supplementary Table 1) of linseed (Linum usitatissimum L.) developed at Main Agricultural Research Station (MARS), University of Agricultural Sciences (UAS), Raichur. Twenty genetically diverse parental genotypes were selected based on their contrasting performance for seed yield and its component traits. Initially, two independent single crosses were made between the selected parents to produce F 1 hybrids. Subsequently, the two F 1 hybrids were intercrossed to generate the double cross population, thereby facilitating greater genetic recombination and broader allelic diversity. The resulting population was advanced through the pedigree method to the F 6 generation by selecting superior plants in each segregating generation.

Experimental design and crop management

The F 6 double cross-derived population, along with the parental lines was evaluated during rabi 2025-26 at Main Agricultural Research Station, Raichur. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. Each genotype was grown in a single row of 3.0 m length with a spacing of 30 cm between rows and 10 cm between plants. All recommended agronomic and plant protection practices were followed uniformly throughout the crop growth period. Observations were recorded on five randomly selected competitive plants from each genotype in each replication for days to 50% flowering, days to maturity, plant height (cm), number of capsules, seeds per capsule, 1000-seed weight (g) and seed yield (kg ha⁻¹). The mean values of these observations were used for statistical analysis.

Statistical analysis

Analysis of Variance (ANOVA) was performed following the procedure described by Panse and Sukhatme (1985) [19] to determine the significance of differences among genotypes. Phenotypic variance and genotypic variance (σ²) were estimated according to Burton (1952) [4] . The Phenotypic Coefficient of Variation (PCV) and Genotypic Coefficient of Variation (GCV) were calculated following Burton and DeVane (1953) [5] Broad-sense heritability (H²) was estimated as suggested by Hanson et al. (1956) [6] , while expected genetic advance (GA) and genetic advance as percent of mean (GAM) was computed using method of Johnson et al. (1955) [9] .

Results and discussion

The highly significant differences (Table 1) among the double cross-derived linseed genotypes for all the studied characters demonstrate the successful generation of genetic variability through integration of genetically diverse parental lines. The substantial variation was observed for seed yield, capsules per plant, plant height, days to flowering, days to maturity; seeds per capsule and thousandseed weight confirms that double cross breeding effectively broadened the genetic base compared with conventional biparental breeding populations. The incorporation of four parental genomes enhances meiotic recombination and facilitates the accumulation of favourable alleles, thereby increasing the probability of recovering superior recombinants in segregating generations (Priya et [13,15,21] . Similar observations on the usefulness of broad-based breeding populations for generating exploitable genetic variability have been reported in linseed by Mohammad et al. (2022) [18] , Kaur et al. (2024) [10] and Rathva et al. (2023) [22] . The estimates of genetic variability (Table 2, Figure 1) clearly demonstrated that the double cross population possessed sufficient phenotypic and genotypic diversity for effective selection. The consistently higher Phenotypic Coefficient of Variation (PCV) than the corresponding Genotypic Coefficient of Variation (GCV) for all characters indicates that environmental factors contributed to phenotypic expression. Nevertheless, the relatively narrow differences between GCV and PCV for days to maturity and days to 50% flowering suggest that these traits were less influenced by environmental conditions and were predominantly governed by genetic factors. Similar trends have been reported in linseed by Abdelaty et al. (2023), Ibrar et al. (2024) [8] and Paul et al. (2017) [20] who also observed relatively small differences between GCV and PCV for maturity-related traits. Among all the characters, capsules per plant exhibited the highest GCV and PCV indicating the presence of substantial exploitable variability. Capsule number is one of the major yield-determining components in linseed because it directly influences the sink capacity of the plant. The high variability observed for this character suggests that recombination resulting from double cross breeding effectively disrupted unfavourable linkage blocks and generated novel gene combinations controlling reproductive development. Similar observations have been reported by Hosseini et al. (2025), Shah et al. (2025) [25] and Markandey et al. (2022) [17] who identified capsule number as one of the most variable and economically important characters in linseed improvement programmes. Heritability (Figure 2) estimates provide valuable information regarding the relative contribution of genetic and environmental factors to phenotypic variation. In the present investigation, high heritability was recorded for days to maturity and days to 50% flowering, indicating that these traits were predominantly controlled by genetic factors and could be selected with greater reliability. However, their comparatively lower genetic advance as a percentage of the mean suggests that improvement through direct phenotypic selection may be gradual because both additive and nonadditive genetic effects may contribute to their inheritance.

Similar conclusions have been drawn by Kaur et al. (2024) [10] , who emphasized that heritability should always be interpreted together with genetic advance to understand the underlying gene action. Moderate heritability coupled with relatively high genetic advance for capsules per plant indicates the predominance of additive gene action, suggesting that selection for this character would be effective in early segregating generations. Traits governed largely by additive genetic effects respond efficiently to phenotypic selection because favourable alleles can be accumulated over successive generations. Comparable findings have been reported by Upadhyay et al. (2019), Rathva et al. (2023) [22] and Mohammad et al. (2022) [18] , who highlighted capsule number as an important criterion for improving seed yield in linseed. In contrast, the relatively low heritability estimates observed for plant height and seed yield indicate that these traits were influenced considerably by environmental factors. Seed yield is a complex quantitative trait resulting from the cumulative interaction of several component characters and environmental conditions consequently, direct selection for seed yield alone is generally less efficient than indirect selection through highly heritable yield components. Similar observations have reported by Dhirhi et al. (2018) [3] , Mahto and Mishra (2025) [14] and Sandhya et al. (2026) [24] who concluded that yield improvement in linseed should be achieved through simultaneous selection for major yieldcontributing traits rather than seed yield alone. The results clearly demonstrate that double cross breeding substantially enhanced the genetic variability available within the segregating population. Unlike conventional biparental populations, which recombine alleles from only two parents, double cross populations integrate favourable alleles from four genetically diverse parents, thereby increasing the frequency of recombination events and generating a wider spectrum of phenotypic variation (Priya et al., 2018; Mahto et al., 2020) [15,21] . Such broad-based populations increase the probability of recovering transgressive segregants possessing superior combinations of favourable alleles for yield and its component traits (Chaudhari et al., 2025; Mohammad et al., 2022) [2,18] . The observed variability parameters indicate that the present double cross population represents a valuable breeding resource for future linseed improvement. Among the evaluated traits, number of capsules emerged as the most reliable selection criterion because of its comparatively high genetic variability, moderate heritability and higher genetic advance. Therefore, selection based on this character is expected to accelerate genetic gain and facilitate the identification of elite recombinants with improved seed yield.

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