Genetic variability, heritability, and genetic advance in interspecific and intergeneric clones of sugarcane

Introduction

Sugarcane (Saccharum spp.), a vital member of the Gramineae family, is globally recognized for its remarkable capacity to accumulate sucrose and for possessing one of the highest biomass production potentials among cultivated plants. Its unparalleled efficiency in converting solar energy into carbohydrates has positioned it as one of the most economically valuable crops for both sugar and renewable bioethanol production (Gianotto et al., 2011; Hoang et al., 2015; Mirajkar et al., 2019) [1,2,3] . Historically, sugarcane has been cultivated on all inhabited continents, contributing substantially to local economies and food industries. In Ethiopia, the historical relevance of sugarcane dates back to the 16th century, when it began appearing in household gardens and farmers' fields, long before formal commercialization (Tena et al., 2018) [4] . Since the establishment of commercial sugarcane production in the country in 1951, the crop has significantly supported both domestic sugar demand and employment generation. It also facilitates the production of by-products such as molasses and bagasse, which are utilized in various industrial applications (Teklemariam, 1991; T. Esayas et al., 2016) [5,6] . As sugarcane continues to gain importance for both food and energy security, breeding efforts have intensified to meet rising demands, particularly under changing environmental conditions. Breeding improved varieties requires a fundamental understanding of genetic variability within the germplasm pool, as well as the ability to evaluate heritable traits and predict genetic gains from selection. Knowledge of the magnitude and nature of genetic variation for yield and its contributing traits forms the foundation for any crop improvement program. In this regard, dissecting the genetic architecture of complex traits enables breeders to better understand the inheritance patterns, enhance selection efficiency, and achieve targeted genetic improvements. Understanding the components of phenotypic variance, particularly the heritable and nonheritable portions, is critical in determining the extent to which a trait can be improved through selection. This process provides insights into the degree of genetic control over a trait and the predictability of its expression under varying environmental conditions (Ullah et al., 2012) [7] . However, high heritability alone is not a guarantee for significant genetic gain. It must be evaluated in conjunction with genetic advance estimates to accurately assess the scope for effective selection and long-term improvement (Amin et al., 2004; Johanson et al., 1955; Udeh & Ogbu, 2011) [8,9,10] . Genetic variability serves as the raw material for plant breeding. Its presence is essential to develop improved cultivars capable of coping with both biotic and abiotic stresses. The diversity within and between genotypes offers the flexibility to select desirable traits for enhancement. By broadening the genetic base of sugarcane through interspecific and intergeneric crosses, breeders can tap into novel alleles that contribute to superior yield, stress tolerance, and adaptability. This expansion of variability becomes even more critical when addressing the challenges of climate change, disease pressure, and resource limitations. Moreover, variance component analysis provides a powerful tool to quantify heritable variation and estimate the potential genetic progress achievable through selection. It helps in identifying promising genotypes for use as parents in hybridization programs, based on their performance and trait inheritance patterns. In sugarcane, where vegetative propagation and complex polyploidy present unique challenges, such assessments become even more vital for strategic planning in breeding (Kumar et al., 2018) [11] . Selection efficiency is also influenced by trait interrelationships. For instance, in multi-trait selection approaches, traits that demonstrate moderate to high heritability along with significant genetic advance, and that are strongly and positively correlated with the primary yield component sugar yield are prioritized (Borém et al., 2016) [12] . Therefore, for effective crop improvement, not only should traits be heritable, but they should also translate into substantial genetic gain under selection pressure. However, the extent of observed variability and heritability is influenced by several factors, including the nature of the genetic material, the target traits, and the environmental conditions under which the plants are evaluated (Dabholkar, 1992; Falconer & Mackay, 1996) [13,14] . These interactions highlight the importance of conducting location-and material-specific studies to draw accurate inferences for breeding applications. Given the importance of exploiting genetic variation for sugarcane improvement, the current study was undertaken to assess the genetic variability, heritability, and genetic advance in a diverse set of interspecific and intergeneric sugarcane clones. This investigation aims to provide essential insights into the potential of these clones for use in future breeding programs, ultimately contributing to the development of high-yielding and resilient sugarcane cultivars.

Materials and Methods

Experimental Material

The present study was conducted using a total of twenty sugarcane genotypes, comprising 17 interspecific and intergeneric clones along with three standard check

Experimental Design

The field experiment was carried out during the cropping season under controlled irrigation and recommended fertilization conditions at the Norman E. Borlaug Crop Research Centre, G. B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand. The trial was laid out in a Randomized Block Design (RBD) with three replications to ensure uniform environmental influence across plots and enhance statistical precision. Standard agronomic practices were followed to ensure healthy crop growth throughout the season.

Data Collection

Observations were recorded on 14 morphological and quality-related traits during the course of the experiment. Germination percentage was calculated 30 days after planting by counting the number of germinated buds and expressing it as a percentage of the total buds planted, providing an estimate of initial plant establishment. Tillers at 90 days were manually counted in each plot to assess early shoot proliferation and plant vigor. Cane length (cm) was measured from the base of the stalk to the top visible dewlap in five randomly selected millable canes per plot, while cane diameter (cm) was recorded at the midpoint of these canes using a Vernier caliper to evaluate stalk thickness. The number of millable canes was determined at harvest by counting the stalks that had matured to a harvestable stage. Juice quality parameters were assessed through brix percentage at 300 and 360 days to evaluate the soluble solids content in the cane juice. Sucrose percentage at 300 and 360 days was estimated by the standard polarimetric method, following established protocols for juice analysis. Purity percentage at both stages was calculated by expressing sucrose content as a proportion of brix and multiplying by 100, serving as an indicator of juice purity. The single cane weight (SCW) was determined by recording the average weight of five randomly selected millable canes using a digital scale. Commercial cane sugar (CCS%), indicating the amount of recoverable sugar, was computed using standard formulae based on brix and sucrose values. Finally, cane yield (t/ha) was calculated by converting the total weight of cane harvested per plot into tons per hectare, based on the plot dimensions.

Statistical Analysis

The statistical analysis for the estimation of genetic parameters, including genotypic and phenotypic coefficients of variation (GCV and PCV), heritability in broad sense, and genetic advance as percent of mean, was performed using the OPSTAT statistical software developed by CCS Haryana Agricultural University, Hisar, India. For data visualization and graphical representation of results, the R software (R Core Team, 2024) [15] was used. Trait distribution plots and comparative graphs were created using the 'ggplot2' package (Wickham, 2016) [16] .

Results and Discussion

The ANOVA results revealed that all observed traits showed significant variation among treatments (genotypes), confirming the existence of substantial genetic variability in the evaluated sugarcane clones (Table 1). Across all 14 characters including germination percentage, tiller number, cane length and diameter, number of millable canes, juice quality traits (Brix, sucrose, purity), single cane weight, commercial cane sugar, and cane yield, the mean sum of squares for treatments was much higher than the corresponding error mean squares. This pattern supports the presence of significant genetic diversity in the test material. In sum, the significant variation observed aligns with studies that emphasize the existence and utility of genetic diversity in sugarcane for targeted selection, particularly when combined with parameters such as heritability and genetic advance (Rani et [17,18,19] . This paves the way for further analysis of genetic parameters (GCV, PCV, heritability, genetic advance) on these same clones for advanced breeding work.

Variability

The analysis of variability parameters revealed substantial differences among the sugarcane clones for all observed traits. For each character assessed, the phenotypic coefficient of variation (PCV) was consistently higher than the genotypic coefficient of variation (GCV), suggesting that environmental factors contributed to the overall phenotypic expression, though their influence was generally moderate. High levels of genotypic and phenotypic variability were particularly notable for tiller count (GCV: 41.78, PCV: 42.39), germination percentage (GCV: 26.98, PCV: 28.51), single cane weight (GCV: 26.24, PCV: 28.03), CCS (GCV: 34.54, PCV: 36.35), cane yield (GCV: 28.61, PCV: 31.07), and number of millable canes at 360 days (GCV: 30.25, PCV: 31.21), signifying a strong genetic basis for variation in these characters (Table 2). In contrast, traits related to juice quality such as Brix and purity exhibited lower GCV and PCV values, pointing to relatively less genetic variation for these attributes (Fig. 1). The environmental coefficient of variation (ECV) values were lower for most traits, indicating acceptable experimental precision for the data. The results indicated a considerable range of variability for critical agronomic and quality traits among the sugarcane genotypes studied. The observation that PCV consistently exceeded GCV aligns with prior reports in sugarcane, underscoring the influence of environment on trait expression, though genetic variation remains the dominant component for most yield-related characters (Khan et al., 2017) [20] . Traits such as tillers, germination percentage, cane yield, single cane weight, CCS, and millable cane number, which exhibited high GCV and PCV, mirror the findings of earlier studies that highlighted the substantial inherent genetic diversity present in sugarcane breeding populations (Rahman et al., 2024; Rani et al., 2024) [21,17] . This sizable genetic variability is essential for effective selection, as it enhances the prospects for realizing substantial genetic improvement in subsequent breeding cycles. For traits where both GCV and PCV were low, particularly for juice quality traits, the range for potential genetic improvement may be narrower, highlighting the need for targeted strategies to enhance these attributes (Prasad et al., 2021). The close correspondence between GCV and PCV for most yield and biomass traits suggests that selection for these traits is less likely to be confounded by environmental effects, thereby increasing the reliability and effectiveness of selection (Khan et al., 2017; Rani et al., 2014) [20,17] . [17,21] . This trend is consistent with previous studies, which demonstrate that selection pressure on such traits can result in effective genetic gain due to the predominance of additive genetic variance ( [20,23,21] . High heritability alone, while important, may not always predict selection success;

the combination with high genetic advance is a more robust indicator that improvements in these traits can be reliably inherited by future generations (Gowda et al., 2016) [24] . On the other hand, for traits such as juice purity and initial sucrose content with lower heritability and genetic advance estimates, direct phenotypic selection is expected to be less effective due to substantial environmental influence or complex genetic control. These findings reinforce long-held breeding principles that heritability estimates should always be interpreted in conjunction with genetic advance to determine the realistic prospects for crop improvement.

Conclusion

The present study revealed substantial genetic variability among the interspecific and intergeneric sugarcane clones for key agronomic and quality traits. Traits such as tiller number, CCS, cane yield, and single cane weight exhibited high heritability coupled with high genetic advance, indicating the predominance of additive gene action and their suitability for improvement through direct selection. In contrast, traits like purity and early sucrose content showed low heritability and genetic advance, reflecting greater environmental influence. These findings provide valuable insights for selecting superior genotypes and designing effective breeding strategies aimed at enhancing yield and quality sugarcane improvement programs.

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