## 3 Discussion  
High variability in germplasm collection is desirable when it comes to introducing new sources of variation in breeding programs. Evaluation and characterization of inherited agronomic traits can improve the identification of the phenotypic clusters within broad geographic groups [21]. In order to assess the phenotypic variability of a pea germplasm collection, the partially-replicated experimental design used in this work allowed successful estimation of broad-sense heritability (He\({}^{2}\)g) using limited seed quantities, significantly reducing the cost of phenotyping [22] a diversity panel containing a large number of lines. Extensive phenotypic variation was present in the diversity panel at both trial sites, illustrated particularly by high coefficients of variation for SY (at IFVCNS and Agro Seed), for TSW (at IFVCNS), and for GPP (at Agro Seed), as well as for SWPP and PL (at IFVCNS) in 2020 and for PH in 2019 and TSW in 2020 (at Agro Seed), while for PH, higher values were recorded in the 2020 season for both trial sites. High heritability of TSW was observed at both IFVCNS and Agro Seed, similar to previous findings [15; 19; 23; 24], showing that this trait is highly genetically controlled. The lowest heritability was recorded for PPP in 2019 and SPP in 2020 for IFVCNS, and for PPP in 2019 and PL in 2020 for Agro Seed, similar to the findings of [19]. Lower heritability for these traits could be due to the significant error variance caused by high environmental influence (particularly with regards to rainfall) and not the narrow genetic variance. Means for PPP, SPP, SWPP, and PH were significantly lower in 2020 than in 2019, which might be the consequence of drought during the flowering period in May 2020 in Serbia (Table S1). The mean for SY was higher in 2020; similar findings were given by [6], where a high amount of precipitation, especially at the flowering stage, positively affected the grain yield of field pea. Means for  
Figure 8: 3D graph of the pea seed yield and pea protein content (the first two principal components from the PCA of the genotype data) for the plant type. (**Left**): seed yield; (**Right**): protein content. B–breeding Line; V–variety; SW–semi-wild; W–wild; L–landrace. PPP, SPP, PH, and SY were lower in 2019 in Belgium. In contrast, TSW was higher in 2019 compared to 2020, which is similar to the findings of [25], where lack of moisture in the pod-filling period led to lower number of pods and seeds per plant. This causes the plants to concentrate their nutrients and energy in the weight of the seeds, giving a higher mass of 1000 seeds, but generally lower yields. The coefficient of variation for all traits in the Serbia trial was generally higher in 2020, which is most likely due to uneven rain distribution during the pea growing season (Table S1), which can affect all the elements of the yielding structure, the length of flowering, and the height and lodging of plants. The phenotypic correlation is conditioned by the relationship among individual traits and the influence of environmental factors [26]. If there is a correlation between two traits, direct selection of one will cause a change in the other. Before initiating any effective selection program, it is necessary to know the association of various traits with each other [27]. The relationship between various traits of peas has been studied previously, but the results were found to vary significantly according to varietal differences and environmental conditions [28; 29; 30; 31]. This study used a very diverse group of pea genotypes and many varieties have a low number of seeds per pod or small grains, therefore diluting the correlation. However, in both trial sites, a positive and significant correlation was found between the traits that represent plant yield (SWPP) with PoL, PPP, SPP, and TSW, similar to previous findings [32; 33], as well as a high positive correlation of SY with TSW and SWPP. The high positive correlation between PPP and SPP is similar to the results of [34].