Introduction

Sweet pepper (Capsicum annuum L.) is an economically important vegetable crop grown extensively under greenhouse and open field conditions worldwide. Increasing market demand and the high cost of imported hybrid seeds underscore the need for efficient local hybrid development. Diallel analysis is a powerful tool for identifying superior parents and determining the genetic control of yield and fruit related traits. By estimating general combining ability (GCA), specific combining ability (SCA), and heterosis, breeders can target promising parental lines and hybrid combinations with strong commercial potential. The present study aimed to evaluate eight inbred pepper lines using a half diallel mating design to determine the nature of gene action and identify high performing hybrids with superior yield and fruit characteristics.

Materials and Methods

Eighty sweet pepper (Capsicum annuum L.) accessions were obtained from the germplasm collection of the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Germany. In the first stage, all accessions were evaluated for a range of morphological, agronomic, and fruit quality traits. Based on fruit yield, fruit quality attributes, pericarp thickness, vitamin C content, fruit uniformity, marketability, suitability for domestic and international markets, and relative tolerance to major production constraints including damping-off, powdery mildew, and temperature fluctuations, eight superior genotypes were selected. These genotypes were subsequently self-pollinated for five consecutive generations to develop highly homozygous inbred lines. The resulting lines were crossed in a half-diallel mating design, generating 28 F₁ hybrids. All hybrids and parents were evaluated during the 2023–2024 growing season in a greenhouse at the South Kerman Agricultural and Education Center (Iran) under a randomized complete block design with three replications. Each plot included 20 plants spaced 30 cm apart, with 100 cm between rows. Two commercial hybrids, Zola and Lombard, were used as standard checks for heterosis estimation. Data were collected for days to maturity, fruit length, fruit diameter, pedicel length and thickness, plant height, fruit weight, total fruit yield across fifteen harvests, and TSS. Combined ANOVA across years was performed using SAS 9.2. Diallel analysis followed Griffing’s Method II, Model I using AGD R v5.1 to estimate GCA, SCA, additive and dominance variances, Baker’s ratio, narrow sense heritability and degree of dominance. Baker’s ratio and heritability were computed according to conventional equations, and dominance degree was estimated following Gravois (1994). Relative heterosis and standard heterosis percentages were calculated for all F₁ hybrids using Microsoft Excel by comparing hybrid performance with the mid-parent values and commercial check cultivars, respectively.



Results and Discussion

Significant genotypic variation was observed for all traits, providing strong evidence of genetic diversity among the parents and confirming their suitability for hybrid breeding. Both GCA and SCA effects were highly significant (P < 0.01) for all traits, indicating that additive and non additive gene actions contributed to trait inheritance. Baker’s ratio values showed that TSS (0.77), plant height (0.73), and fruit diameter (0.60) were predominantly influenced by additive gene action. In contrast, traits such as fruit yield (0.37), pedicel thickness (0.35), and days to maturity (0.43) were mainly governed by non additive effects. These observations were reinforced by narrow sense heritability estimates, which were moderate to high for fruit diameter (0.58), pedicel length (0.60), and TSS (0.76), but lower for yield (0.35) and pedicel thickness (0.38). Degrees of dominance greater than 1.0 for fruit yield (1.83), days to maturity (1.64), and pedicel thickness (1.90) indicated overdominance. Fruit weight also showed evidence of overdominance (1.33). On the other hand, incomplete dominance (degree <1.0) was detected for fruit length, fruit diameter, plant height, and TSS. These results align with previous studies demonstrating the importance of non additive gene action in pepper for key yield traits. Analysis of GCA revealed that parental line 400 was the most consistent and desirable general combiner for fruit yield, fruit weight, pedicel traits, and fruit diameter. Line 245 also performed well for yield related traits. Line 318 showed favorable GCA values for fruit weight and pedicel thickness, while lines 241, 208, and 265 exhibited significantly negative GCA for days to maturity, identifying them as good combiners for earliness. SCA effects identified several highly promising hybrid combinations. The hybrids 318 × 245, 296 × 400, 245 × 400, and 318 × 400 achieved the highest yields, ranging from 132 to 159 t ha⁻¹, all outperforming the parental means and commercial checks. These hybrids also showed strong SCA effects for fruit weight, fruit length, and pedicel thickness, indicating superior gene complementation and strong non additive interactions.

Relative and standard heterosis analyses revealed considerable hybrid vigor for fruit yield and several related traits. The hybrids 296 × 400, 318 × 245, 245 × 400, and 318 × 400 exhibited the highest levels of heterosis and achieved fruit yields ranging from 133 to 160 t ha⁻¹, substantially exceeding both parental means and commercial check cultivars. Among these, the cross 296 × 400 showed the highest standard heterosis for fruit yield (132.85%), accompanied by strong positive heterosis for fruit weight, fruit diameter, pedicel thickness, and TSS. Similarly, hybrids 296 × 245 and 296 × 265 displayed exceptionally high standard heterosis values exceeding 100% for fruit yield, highlighting their commercial potential. The positive relative heterosis observed for fruit weight, fruit length, fruit diameter, and TSS suggests that the superiority of these hybrids resulted from the simultaneous improvement of several yield components and quality traits.

Conclusion

This study successfully identified superior parental lines and high performing hybrid combinations using half diallel analysis. Line 400 was the strongest general combiner across multiple traits, while hybrids 318 × 245, 296 × 400, 245 × 400, and 318 × 400 showed outstanding yield performance (>150 t ha⁻¹) and significant positive heterosis for several yield related traits. Considering the predominance of non additive gene action for key economic traits, heterosis breeding is highly effective for sweet pepper improvement. Although results were obtained under a single greenhouse environment, multi location and multi year trials are recommended to validate hybrid stability and determine their suitability for commercial seed production.