Genetic variability, heritability and genetic advance for yield and quality traits in sponge gourd [Luffa cylindrica (L.) M. Roem.]

Introduction

Sponge gourd [Luffa cylindrica (L.) M. Roem.], commonly referred to as smooth luffa or ghiya tori, is a major cucurbitaceous vegetable cultivated extensively across tropical and subtropical regions of Asia, Africa and Latin America. In India, its cultivation is concentrated in Uttar Pradesh, Bihar, West Bengal, Andhra Pradesh and Maharashtra, primarily during the Kharif season. The crop occupies a dual economic position: the immature fruits serve as a nutritious culinary vegetable rich in carbohydrates, proteins, calcium and ascorbic acid (Whitaker and Davis, 1962) [30] , while the dried fibrous skeleton of mature fruits finds wide application as a natural sponge, loofah pad, industrial filter and handicraft raw material. Despite these attributes, sponge gourd remains comparatively underexploited in terms of systematic genetic improvement relative to bottle gourd, bitter gourd and ridge gourd. The foundation of any successful crop improvement programme rests on the magnitude and nature of genetic variability present in the breeding material. The genotypic and phenotypic coefficients of variation (GCV and PCV) are widely used indices to quantify the extent of genetic and total phenotypic variation among genotypes (Burton, 1952; Singh and Chaudhary, 1985) [8,26] . A close correspondence between GCV and PCV indicates minimal environmental influence on trait expression. Heritability in broad sense (h²ᴮ), defined as the proportion of total phenotypic variance attributable to genetic factors (Allard, 1960) [2] , determines the efficiency with which phenotypic selection reflects underlying genetic differences. However, heritability alone does not predict actual selection gain, since high heritability may arise from non-additive gene effects not fixable by selection (Lush, 1940) [19] . Genetic advance as percentage of mean (GAM), when interpreted jointly with heritability, provides a reliable indicator of gene action: high heritability with high GAM points to additive effects and ensures productive mass or pedigree selection, while high heritability with low GAM implies dominance and epistatic variance (Johnson et al., 1955) [12] . Although several workers have estimated genetic parameters in sponge gourd, comprehensive simultaneous evaluation of parents, F₁ hybrids and F₂ populations for all major morphological, yield and quality characters remains limited. (Gantayat et al., 2025) [10] and Billur et al., (2025) [6] recently reported variability parameters in sponge gourd, while (Annigeri et al., 2020, Bisen et al., 2016) [4,7] and (Abhijeet et al., 2018) [1] have contributed important baseline data. Quality-related traits such as sugar fractions, ascorbic acid and shelf life remain comparatively less studied relative to yield traits. The present investigation was undertaken to estimate GCV, PCV, h²ᴮ, GA and GAM for twenty characters across three populations, with the aim of identifying traits amenable to direct selection and providing a quantitative basis for designing breeding strategies in sponge gourd.

Materials and Methods

The experiment was conducted at the Vegetable Research Farm, Department of Vegetable Science, CSAUA&T, Kanpur (latitude 26°28'N, longitude 80°19'E, altitude 126 m), Uttar Pradesh, India during Kharif 2025-26. Ten genetically diverse sponge gourd parents were selected for the study: Kashi Divya, Kashi Kalyani, VRSG-1716, VRSG-1731, Kashi Vandana, Kashi Shreya, VRSG-175, VRSG-1710 and VRSG-196 were procured from ICAR-Indian Institute of Vegetable Research (IIVR), Varanasi, while Kalyanpur Hari Chikni was a locally adapted variety sourced from CSAUA&T, Kanpur. These ten parents were crossed in all possible combinations under a half-diallel mating design (Griffing, 1956; Method II, Model I) [5] to generate 45 F₁ hybrids, which were subsequently selfpollinated to produce 45 F₂ populations. All 100 entries (10 parents + 45 F₁ + 45 F₂) were evaluated in Randomized Block Design with three replications. Each entry was sown in a single row of 4.5 m with row-to-row spacing of 0.75 m and plant-to-plant spacing. Plants were allowed to trail freely on the ground along the bed. Standard agronomic practices and recommended fertilizer doses (100:60:60 kg NPK/ha) were followed uniformly. Observations were recorded on five randomly selected competitive plants per entry per replication for twenty characters: days to first male flower (DFMF), days to first female flower (DFFF), node number of first male flower (NNMF), node number of first female flower (NNFF), days to first harvest (DFH), vine length (VL), number of primary branches per plant (NPB), average fruit weight (AFW), fruit length (FL), fruit diameter (FD), number of fruits per plant (NFP), fruit yield per plant (FY), fruit yield per plot (FYPP), dry matter content (DM), total soluble solids (TSS), nonreducing sugar (NRS), reducing sugar (RS), total sugar (TS), ascorbic acid (ASC) and shelf life (SL). Analysis of variance was performed following Panse and Sukhatme (1985). Genotypic (σ²g) and phenotypic (σ²p) variances, GCV and PCV (Burton, 1952) [8] , heritability in broad sense h²ᴮ (%) = (σ²g/σ²p) ×100 (Allard, 1960) [2] and genetic advance at 5% selection intensity GA = k×√σ²p×h²ᴮ, k = 2.063 (Johnson et al., 1955) [12] were estimated. GCV and PCV were classified as low (<10%), moderate (10-20%) or high (>20%) (Sivasubramanian and Madhavamenon, 1973) [27] , and GAM as low (<10%), moderate (10-20%) or high (>20%) (Johnson et al., 1955) [12] .

Results and Discussion

Analysis of variance (Table 1 and Figure 1) revealed highly significant (p<0.01) differences among genotypes for all twenty characters studied in parents, F₁ hybrids and F₂ populations of sponge gourd, confirming the existence of adequate genetic variability amenable to selection. Mean squares due to replications were non-significant for the overwhelming majority of trait-population combinations, confirming experimental precision and uniformity of field management. Detailed estimates of variability parameters are presented in (Table 2 andFigure 2) discussed below. Similar highly significant differences among genotypes for all quantitative traits were reported by (Abhijeet et al., 2018) [1] , (Singh et al., 2019) [25] , (Kumar et al., 2022) [18] and (Sashi Suman et al., 2024) [23] in sponge gourd.

Phenological and Vegetative Characters

Days to first male flower (DFMF) ranged from 31.50 to 38.12 days (mean 35.29) in parents, with low GCV (6.47%) and PCV (6.80%), indicating narrow phenotypic and genotypic variability for this trait. Despite the limited range, heritability was very high (h²ᴮ = 90.47%) with moderate GAM (12.70%), confirming that the observed variability, though small, is predominantly genetic and additive in origin. In F₁ hybrids, DFMF ranged from 31.12 to 36.86 days (mean 34.29; h²ᴮ = 69.38%; GAM = 7.03%), while F₂ populations showed h²ᴮ of 61.33% and GAM of 7.15%. The gradual decline in heritability across generations reflects some contribution of dominance variance in hybrid populations. Similar low GCV with high heritability for DFMF was reported by (Gantayat et al., 2025) [10] and (Billur et al., 2025) [6] in sponge gourd. Low GCV for days to first male flower was also reported by (Kasera et al., 2018) [13] and (Prabakaran et al., 2025) [21] in sponge gourd, while (Abhijeet et al., 2018) [1] noted that node number at first staminate flower recorded the highest GCV (36.20%), indicating greater variability when flowering is measured by node position rather than days. Days to first female flower (DFFF) in parents ranged from 36.53 to 44.33 days (mean 40.55), with low GCV (5.70%), high h²ᴮ (81.96%) and moderate GAM (10.65%). The narrow GCV-PCV difference across all three generations confirms minimal environmental modification of flowering time. In F₁ hybrids, DFFF ranged from 36.58 to 42.20 days (mean 39.43; h²ᴮ = 66.25%), and F₂ populations recorded h²ᴮ of 56.88%, reflecting reduced additive variance in segregating populations. Node number of first male flower (NNMF) showed low GCV (3.31%) and PCV (4.42%) with moderate h²ᴮ (56.11%) and low GAM (5.11%) in parents, declining sharply to h²ᴮ of 34.95% in F₁ and 16.47% in F₂, with consistently very low GAM. This pattern indicates the predominance of non-additive gene action for NNMF, making early-generation selection ineffective. Node number of first female flower (NNFF) showed a comparable decline from 61.23% (parents) to 32.42% (F₂), confirming substantial dominance variance. Hybridization-based approaches are more appropriate for improving these traits, consistent with observations of (Annigeri 2020) [4] . High heritability with moderate genetic advance for days to first female flower was similarly observed by (Kasera et al., 2018) [13] with h² = 90.4% and Saudamini (Ray et al., 2021) [24] in sponge gourd. Days to first harvest (DFH) ranged from 43.50 to 53.67 days (mean 48.79) in parents, with low GCV (8.07%) but very high h²ᴮ (94.30%) and moderate GAM (16.16%), indicating strong additive genetic control. This pattern persisted across generations: F₁ h²ᴮ = 79.69% and F₂ h²ᴮ = 71.24%, confirming that selection for early harvest will be reliable. Vine length (VL) showed moderate h²ᴮ (71.39%) and moderate GAM (12.36%) in parents, declining to 43.73% in F₂, suggesting partial non-additive contribution in segregating populations. Number of primary branches (NPB) recorded high h²ᴮ (90.54%) and moderate GAM (15.86%) in parents, declining to 44.36% in F₂, consistent with involvement of dominance variance in branching habit. High heritability for days to first harvest was corroborated by (Prabakaran et al., 2025) [21] and (Priyanka et al., 2025) [22] in sponge gourd.

Yield and Yield-Contributing Characters

Average fruit weight (AFW) ranged from 113.72 to 168.29 g (mean 140.38 g) in parents, with moderate GCV (10.96%), high h²ᴮ (80.68%) and high GAM (20.31%), collectively indicating additive gene action and good scope for mass selection. In F₁ hybrids, AFW showed h²ᴮ of 65.46% and GAM of 11.24%, and F₂ populations recorded h²ᴮ of 54.67% and GAM of 10.55%. The slight decline reflects modest inbreeding depression and some nonadditive contribution. These results are in agreement with (Gantayat et al., 2025) [10] and Aslam et al., (2024) [5] . High heritability coupled with high genetic advance for average fruit weight was similarly documented by (Abhijeet et al., 2018) [1] , (Kasera et al., 2018) [13] with h² = 89.4% and GA% = 49.85%, (Singh et al., 2019) [25] , (Annigeri 2020) [4] with h² = 71.8% and GA% = 33.6%, (Kumar et al., 2020) [16] , (Sashi Suman et al., 2024) [23] and (Prabakaran et al., 2025) [21] in sponge gourd. Fruit length (FL) emerged as one of the most selectionresponsive traits. Parents showed high GCV (15.73%), very high h²ᴮ (96.99%) and very high GAM (31.96%) the most favourable combination for selection response. In F₁ hybrids, h²ᴮ was 87.18% and GAM 19.99%, while F₂ populations recorded h²ᴮ of 82.82% and GAM of 19.87%. The uniformly high estimates across all generations confirm strong additive genetic control and predict rapid, consistent gains from selection for fruit length. Fruit diameter (FD) showed high h²ᴮ in parents (82.28%) but low GAM (11.18%), declining sharply in F₁ (56.20%; GAM 5.42%) and F₂ (46.10%; GAM 5.36%), indicating notable dominance variance that limits early-generation selection utility. Very high heritability and high genetic advance for fruit length were similarly reported by (Singh et al., 2019) [25] [25] , (Kumar et al., 2020) [16] , (Kumar et al., 2022) [18] and (Prabakaran et al., 2025) [21] in sponge gourd. Number of fruits per plant (NFP) is a primary yield determinant in sponge gourd. In parents, NFP ranged from 12.53 to 23.67 (mean 18.17), with high GCV (18.97%), very high h²ᴮ (94.89%) and very high GAM (38.12%), providing compelling evidence for additive inheritance. In F₁ hybrids, h²ᴮ was 81.43% and GAM 21.38%, and F₂ populations showed h²ᴮ of 70.92% and GAM of 20.91%. The persistent high heritability and GAM across all three generations confirm the effectiveness of early-generation selection for NFP. (Abhijeet et al., 2018) [1] and (Bisen et al., 2016) [7] similarly reported high GCV and heritability for this trait. High heritability and high genetic advance for number of fruits per plant were reported by (Kasera et al., 2018) [13] with h² = 92.8% and GA% = 49.83%, (Singh et al., 2019) [25] with h² = 80.1% and GA% = 39.2%, (Annigeri 2020) [4] with h² = 76.4% and GA% = 38.2%, (Kumar et al., 2020) [16] with h² = 92.49%, (Kumar et al., 2022) [18] , (Kousthubha et al., 2023) [14] and (Prabakaran et al., 2025) [21] in sponge gourd. Fruit yield per plant (FY) recorded the highest GAM among all characters: 26.94% GCV, 96.51% h²ᴮ and 54.60% GAM in parents, the most desirable combination a plant breeder can encounter, confirming overwhelming additive genetic control and predicting substantial gains from selection. In F₁ hybrids, FY ranged from 2.05 to 4.06 kg (mean 2.89 kg; h²ᴮ = 85.41%; GAM = 31.59%), and F₂ populations recorded h²ᴮ of 77.02% and GAM of 30.55%. The uniformly high GAM (>30%) across all generations strongly supports direct selection for FY in any generation. Fruit yield per plot (FYPP) closely mirrored FY (parents: GCV = 26.84%; h²ᴮ = 93.75%; GAM = 53.61%), as expected. These findings are consistent with Billur et al., (2025) [6] , Abhijeet et al., (2018) [1] and Bisen et al., (2016) [7] . These findings conform with Singh et al., (2019) [25] reporting h² = 82.4% and GA% = 37.8%; Annigeri (2020) [4] with GCV = 29.6% and PCV = 34.8%; Saudamini Ray et al., (2021) [24] with h² = 84.3%; (Kumar et al., 2022) [18] ; Sashi Suman et al., (2024) [23] with GCV = 24.96%; and (Prabakaran et al., 2025) [21] and (Gantayat et al., 2025) [10] in sponge gourd, all reporting high GCV, heritability and genetic advance for fruit yield per plant.

Quality Characters

Dry matter content (DM) showed moderate GCV (10.92%), high h²ᴮ (90.72%) and high GAM (21.45%) in parents, indicating additive gene effects and good scope for selection. Both F₁ (h²ᴮ = 74.87%; GAM = 12.13%) and F₂ (h²ᴮ = 68.76%; GAM = 11.93%) maintained relatively high heritability, suggesting persistent genetic control across generations. Total soluble solids (TSS) showed low GCV (3.88%) and moderate h²ᴮ (61.40%) in parents, but heritability declined steeply to 26.53% in F₁ and 29.84% in F₂, with very low GAM throughout (2.36-6.27%), clearly indicating substantial non-additive gene influence and environmental sensitivity. Selection for TSS in early generations is therefore unlikely to be productive. High heritability for dry matter content was similarly noted by (Kumar et al., 2019) [15] and (Kumar et al., 2022) [18] in sponge gourd. Non-reducing sugar (NRS) showed a favourable pattern with high h²ᴮ (87.61%) and moderate GAM (19.94%) in parents, persisting at high levels in F₁ (73.14%) and F₂ (66.29%), suggesting predominantly additive genetic control. Total sugar (TS) similarly showed high h²ᴮ (87.31%) and moderate GAM (16.30%) in parents. Reducing sugar (RS) showed moderate h²ᴮ in parents (75.38%) declining progressively in F₁ (49.32%) and F₂ (47.51%), indicating partial dominance involvement. Ascorbic acid content (ASC) showed moderate h²ᴮ (59.49%) with low GAM (6.66%) in parents, declining further in F₁ (43.60%) and F₂ (36.97%), confirming the influence of nonadditive gene action and environmental factors on this biochemical trait. Marker-assisted selection in advanced generations would be more appropriate for ASC improvement. High heritability for sugar fractions was corroborated by (Kumar et al., 2019) [15] in sponge gourd, indicating the scope for simultaneous improvement of yield and quality characters.

Shelf life (SL) emerged as one of the most promising traits for direct selection: high GCV (15.84%), very high h²ᴮ (96.34%) and very high GAM (32.08%) in parents, remaining high in F₁ (h²ᴮ = 83.80%; GAM = 18.85%) and F₂ (h²ᴮ = 80.84%; GAM = 18.87%). The consistently high heritability and high GAM across all three populations confirm additive gene control of shelf life and predict excellent response to selection. Genotypes with SL exceeding 8 days would be particularly valuable for distant market supply chains. These results corroborate the findings of (Gantayat et al., 2025) [10] and (Amulya et al., 2025) [3] . Comparable high heritability estimates for fruit quality traits were reported by (Sashi Suman et al., 2024) [23] , (Yadav et al., 2024) [29] and (Vidya et al., 2025) [28] in sponge gourd.

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