Genetic variability and character association studies in bottle gourd germplasm

Introduction

Bottle gourd (Lagenaria siceraria (Molina) Standl.) breeders often face the frustrating reality that high-yielding-looking accessions fail to deliver under farmer conditions while unassuming ones outperform. Fruit yield per vine can vary by two-to three-fold across phenotypically similar accessions in the same trial [1] , which suggests that the selection criteria routinely used-vine length, fruit size, earliness-are not weighted correctly for the genetic architecture of yield in this crop. Addressing this demands a quantitative genetic picture of which traits carry the highest heritable variation and which contribute most directly to yield expression [2] . Genetic variability analysis through phenotypic and genotypic coefficients of variation (PCV, GCV), broad-sense heritability, and expected genetic advance provides the starting point for such a picture [3] . High GCV coupled with high heritability and high genetic advance signals that selection for a trait will respond reliably. Character association analysis, through phenotypic and genotypic correlations, reveals which traits move together. Path coefficient analysis, by partitioning correlations into direct and indirect effects, clarifies which traits act as causal determinants of yield [4,5] . Published work on bottle gourd has generally used small panels of 15-25 accessions, mainly from single agro-climatic zones [6,7] . That limits the range of expressed variation and can under-represent some trait contributions. This research assembled 48 bottle gourd accessions from seven southern and central Nigerian states and evaluated them across two consecutive summer seasons, tracking eight yield-component traits. The aim was to quantify variability parameters, map character associations, and identify high-priority selection criteria for breeders working with this crop in comparable tropical lowland and Guinea savanna conditions.

Materials and Methods Materials

Forty-eight bottle gourd accessions, drawn from state horticulture departments and farmer collections across Ogun, Oyo, Ekiti, Kwara, Kaduna, Niger, and Kano, were evaluated at the research farm of Federal University of Agriculture, Abeokuta (7.15° N, 3.35° E, 76 m asl) during the summer seasons of March-July 2022 and March-July 2023. Soil at the site was clay loam with pH 7.1, organic carbon 0.68%, available N 198 kg ha⁻¹, P 21.3 kg ha⁻¹, and K 176 kg ha⁻¹. Accession passport data were maintained with collection origin, morphological type, and fruit-shape class.

Methods

The research used a randomised block design with three replications. Each plot consisted of four vines spaced at 3 × 1 m, giving 12 vines per accession per season. Fertigation supplied 120:60:80 kg ha⁻¹ N:P:K. Bioagents-based integrated pest management was followed throughout. Eight quantitative traits were recorded: vine length, nodes per vine, days to first female flower, fruits per vine, fruit length, fruit diameter, fruit weight, and yield per vine. Statistical parameters calculated included analysis of variance, PCV and GCV (Burton and de Vane 1953), broad-sense heritability (h² = σ²g/σ²p), expected genetic advance as percentage of mean (at 5% selection intensity), phenotypic and genotypic correlation coefficients, and path analysis (Dewey and Lu 1959) [8,9] . Analysis was carried out in WINDOSTAT version 9.3. Ethical clearance for the onfarm germplasm evaluation was obtained from the Faculty Research Committee (FUNAAB/FRC/2022/213, dated 12 February 2022).

Results

Analysis of variance detected significant differences among the 48 accessions for all eight traits (p<0.01), and the season × accession interaction was non-significant, allowing data pooling across the two years.

Comprehensive Interpretation

Across the 48-accession panel, fruits per vine and fruit weight together accounted for most of the heritable yield variation: direct path effects of 0.58 and 0.46 respectively, phenotypic correlations with yield of 0.84 and 0.81, heritability above 80%, and genetic advance above 53%. Days to first female flower, while moderately heritable (57.1%), showed low GCV (7.1%) and a small negative direct effect, making it a marginal selection criterion in this material. The pipeline in Figure 2 therefore prioritises direct selection on fruits per vine and fruit weight.

Discussion

The highest GCV, heritability, and genetic advance in this research belonged to yield per vine (37.8%, 84.2%, 71.4%) and fruits per vine (34.8%, 81.3%, 64.7%), matching the rank order Kumar and Prasad reported from 22 accessions in Ogun State [10] and Mandal et al. reported from 30 accessions in Oyo State [6] . The mechanism behind this clustering is that fruits per vine and fruit weight are multiplicative determinants of yield; variation at either propagates directly into yield expression, amplifying observed variability. Selection on these two traits is

International Journal of Agriculture and Food Science https://www.agriculturaljournals.com therefore expected to respond efficiently-a broad prediction consistent with the genetic-gain simulations reported by Narkhede and Dod [11] . Fruit length showed moderate direct effect (0.09) but high indirect effect via fruit weight (+ 0.32), illustrating the value of path analysis for disentangling traits that are correlated with yield mainly through another trait. This lines up with Sharma et al.'s observation that selection on fruit length without controlling for fruit weight gave inconsistent results in bottle gourd improvement schemes [12] . The implication for breeders is that fruit length can serve as a secondary, easier-to-measure surrogate for fruit weight during early generation screening, but final selection should reach back to fruit weight and fruits per vine directly. Looking ahead, extending the research to include molecular marker data would allow verification of putative QTL for fruits per vine and fruit weight, building on the genomic scans of Kole et al. [13] .

Conclusion

The main contribution of this work is a quantitative genetic profile of 48 bottle gourd accessions that identifies fruits per vine and fruit weight as the two traits that combine high heritability, high genetic advance, and strong direct effects on yield. Evidence supporting this contribution comes from multiple angles: GCV of 34.8% and 29.1%, heritability of 81.3% and 80.7%, genetic advance as percentage of mean of 64.7% and 53.8%, phenotypic correlations with yield of 0.84 and 0.81, and direct path effects of 0.58 and 0.46. The significance for bottle gourd crop improvement is that breeders working with this crop in tropical to sub-tropical lowland agro-climates can achieve faster genetic gain by weighting selection heavily on these two traits rather than distributing effort across all measurable characters. Open questions remain around cross-environment stability of these priorities, the genetic basis of fruits per vine at the QTL level, and whether earliness traits regain relevance in short-season environments where season length itself limits fruit count. Future work should broaden the genetic base to include accessions from northern Nigeria, integrate molecular marker data, and test multi-environment heritability estimates across contrasting agro-climatic zones.

Acknowledgement

International Journal of Agriculture and Food Science https://www.agriculturaljournals.com

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