Field pea (Pisum sativum L.) is a cool-season crop that provides nutrition for people and feed for livestock. Its yield is often reduced by environmental stresses, especially heat (Dave et al., 2024). High temperatures during the reproductive stage are particularly harmful, even though the crop is grown in climates from semi-arid to temperate regions with the temperatures (7-30)°C (Olle et al., 2020). Heat stress disrupts processes like photosynthesis, pollen function, fertilization and pod development, which lowers yield (Kumar et al., 2025). The problem is more in late sowing, when flowering and seed filling coincide with high temperatures, causing major yield losses. Studying genetic variation and trait interactions under heat stress is key to developing better, heat-tolerant varieties.
       
Sufficient genetic variability enables the selection of superior genotypes. Assessing this variation helps breeders identify desirable parents and formulate effective selection strategies. Parameters such as GCV, PCV, heritability and genetic advance provide valuable information on the nature of variability and the expected response to selection. These parameters help to identify traits that are more likely to respond to selection. Correlation analysis identifies the association of seed yield with its related traits, whereas path coefficient analysis separates these associations into direct and indirect effects, thereby identifying characters that contribute most effectively to yield improvement (Singh and Kumar, 2023). Such information is particularly useful when selecting traits for simultaneous improvement under contrasting environments.
       
In this context, the present investigation focused on evaluating genetic variability, heritability, correlation and path coefficients for yield and its associated traits in ten parental lines and their forty-five F1 hybrids under timely and late-sown conditions. The findings are expected to facilitate the identification of key traits for developing high-yielding and heat-tolerant field pea genotypes.

The experimental trials were conducted across two Rabi seasons (2023-24 and 2024-25). In the first season, ten selected field pea genotypes were crossed using a half-diallel design to produce 45 F1  hybrids. In the next season, these hybrids and their parents were tested under timely (5 Nov 2024) and late sowing (5 Dec 2024) in RBD with three replications at the research farm of Genetics and Plant Breeding Research, Acharya Narendra Deva University of Agriculture and Technology. Meteorological parameters, including maximum and minimum temperature, relative humidity, rainfall and other weather variables recorded during the crop growth period, were collected from the university meteorological observatory and are illustrated in Fig 1a and 1b.




       
Late sowing exposed the crop to higher temperatures during reproduction, causing heat stress. Data were recorded on five randomly selected plants for eleven characters, namely days to flowering, days to maturity, primary branches/plant, secondary branches/plant, plant height, pods/plant, seeds/pod, harvest index, seed index, Biological yield/plant and seed yield/plant. The recorded data were subjected to ANOVA and other statistical analyses using R software.

Analysis of variance
 
ANOVA for eleven morpho-agronomic traits under timely-sown (Table 1) and late-sown (Table 2) conditions indicated significant genotypic differences, demonstrating considerable genetic variability within the experimental material. Considerable variation among the evaluated genotypes was observed for flowering time, maturity, plant height, pods/plant, biological yield/plant, harvest index and seed yield/plant, highlights the existence of diverse genetic backgrounds, Consequently, this offers considerable scope for selecting superior genotypes. and successful crop improvement programme.




 
GCV, PCV, heritability and genetic advance
 
Table 3 and 4 indicate that PCV were consistently greater than GCV across all the studied traits in both environments, reflecting the involvement of environmental factors. High PCV and GCV estimates were observed for seed yield, secondary branches/plant, biological yield/plant and pods/plant, reflecting considerable variation for these characters. Similar observations have been noted by Afreen  et al. (2017) and Sharma  et al. (2023). Conversely, days to maturity exhibited the least variability in both environments. The small differences between GCV and PCV for traits such as biological yield/plant, seed yield/plant and plant height suggests stronger genetic control with minimal environmental effects, whereas larger differences noted for harvest index and seeds/pod, indicate greater environmental sensitivity.




       
Heritability and genetic advance exhibited considerable variation among the studied traits under both timely and late-sown environments, reflecting differences in their underlying genetic regulation. Higher heritability values were obtained for biological yield/plant, plant height, seed yield/plant, pods/plant, secondary branches/plant and seed index, which suggests that the observed phenotypic differences were mainly explained by genetic factors. In comparison, days to flowering, days to maturity, primary branches/plant and harvest index expressed moderate heritability, whereas seeds/pod displayed relatively lower heritability, suggesting a stronger influence of environmental conditions on its expression.
       
Genetic advance estimates varied considerably among the evaluated traits. Biological yield/plant recorded the high genetic advance in both environments, followed by seed yield/plant, pods/plant and secondary branches/plant. Similar observations have been reported by Singh  et al. (2019). The simultaneous occurrence of high heritability and genetic advance for traits including Biological yield/plant, seed yield/plant, pods/plant and secondary branches/plant indicates that substantial improvement can be obtained through phenotypic selection, making them useful targets in a field pea breeding programme, particularly under late-sown conditions where heat stress limits productivity.
 
Correlation coefficient
 
Table 5 and 6 showed the pattern of trait associations remained largely consistent across both sowing conditions. Similar trends have been reported by Singh  et al. (2017). Seed yield exhibited favourable associations with most of the yield contributing traits under both environments. In contrast, days to flowering and days to maturity were negatively associated with seed yield/plant, suggesting that early-flowering and early-maturing genotypes possess greater potential to perform better under terminal heat stress, particularly in late-sown conditions.




       
Genotypic correlations were generally stronger than the corresponding phenotypic correlations, indicating that genetic factors contributed more strongly to trait associations than environmental effects. Days to flowering showed a positive relationship with days to maturity, whereas both traits were negatively associated with plant height, pods/plant, biological yield/plant and seed yield/plant, suggesting that genotypes with early flowering and maturity are more productive, especially under late sown conditions.
       
Days to flowering displayed a positive relationship with days to maturity, whereas it showed significant negative associations with plant height, primary branches/plant, pods/plant, biological yield/plant and seed yield/plant. Likewise, days to maturity was negatively correlated with pods/plant, Biological yield/plant and seed yield/plant, reflecting the advantage of early phenological development to improve productivity, Similar findings were reported by Kumar et al. (2014).
       
Furthermore, Biological yield/plant maintained strong positive relationships with pods/plant, seeds/pod, primary branches/plant, secondary branches/plant and seed yield/plant in both the environments. These associations emphasize the role of biomass production in determining seed yield/plant. Harvest index also exhibited positive relationships with seed yield/plant under timely sowing; however, these associations became comparatively weaker under late sown conditions, suggesting that its contribution declined under heat stress.
       
The consistent positive correlations among traits across studies highlight their usefulness for selection in improving seed yield/plant, particularly via pods/plant, seeds/pod and Seed index (Georgieva et al., 2015; Sharma et al., 2023). Pods/plant, biological yield/plant, primary branches/plant and secondary branches/plant were identified as major contributors to seed yield/plant under both timely and late-sown conditions, highlighting their usefulness in improving yield across different environments, especially under late sown stress conditions. Fig 2a and 2b present the genotypic and phenotypic correlation heatmaps, respectively, under timely-sown conditions, whereas Fig 3a and 3b depict the corresponding genotypic and phenotypic correlation heatmaps under late-sown conditions in field pea.








 
Path coefficients analysis
 
Path coefficient analysis was used to determine the relative contribution of individual traits to seed yield/plant by partitioning their correlations into direct and indirect effects. The results obtained under timely and late-sown environments are given in Table 7 and 8, while the corresponding genotypic and phenotypic path diagrams are illustrated in Fig 4 and 5. Under timely-sown conditions, biological yield/plant produced the strongest positive direct effect on seed yield/plant at genotypic and phenotypic levels, indicating that improvements in biomass production are predicted to enhance grain yield under favourable growing conditions. In contrast, its direct contribution was comparatively lower in late sown condition, where terminal heat stress altered the relative importance of yield components. Under late sown conditions, pods/plant made the greatest direct contribution to seed yield/plant. Seeds/pod and seed index also made comparatively greater direct contributions under heat-stress conditions than timely sown condition, highlighting their importance in maintaining productivity when plants are exposed to elevated temperatures during the reproductive stage. Harvest index contributed positively under timely sowing but its influence declined under late sowing, indicating that its effectiveness was reduced under stress conditions.













Days to flowering exerted a negative direct effect on seed yield/plant under both environments, suggesting that earlier flowering genotypes possess a greater capacity to maintain productivity, particularly when exposed to terminal heat stress. Examination of indirect effects further showed that several traits influenced seed yield/plant indirectly through biological yield/plant under late sown conditions, however, pods/plant and seeds/pod represented the major indirect contributors to yield improvement.
       
The residual effects were relatively low under both environments, suggesting that the characters included in the analysis captured most of the variability observed in seed yield/plant. Overall, the results emphasize that biomass related traits are more important under favourable environments, whereas reproductive attributes, particularly pods/plant and seeds/pod, become increasingly important under late sown, heat-stressed conditions. Similar observations have been reported by Tofiq  et al. (2015).

The present investigation demonstrated the considerable genetic diversity among the evaluated field pea genotypes under timely and late sown environments, indicating good prospects for genetic improvement. Although environmental factors influenced the expression of all the studied traits, biological yield/plant, seed yield/plant, pods/plant and secondary branches/plant consistently exhibited favourable genetic parameters, suggesting that these characters can be improved effectively through selection. Correlation and path coefficient analyses further identified biological yield/plant, pods/plant, seeds/pod and seed index as the main contributors to seed yield/plant. Under heat stress conditions, reproductive traits, particularly pods/plant and seeds/pod, assumed greater importance in determining yield performance. Therefore, these may be serve as valuable traits for developing high-yielding and heat tolerant field pea cultivars suitable for both timely and late sown environments.

The present study was supported by Department of Genetics and Plant Breeding, Acharya Narendra Deva University of Agriculture and Technology, Kumarganj, Ayodhya-224 229, (Uttar Pradesh), India.

The author declares that there are no conflicts of interest regarding the publication of this article, No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.