Statistically significant difference among the parents and crosses were observed for yield and its component traits. Mean performance of the parents showed that IC 632961 performed better in term of pod length, average pod weight, pod dry weight, 100 seed weight and seed yield but it was late in days to 50% flowering and days to harvest. In contrary, variety; Arka Arjun found as busy, earliest in 50% flowering having long pod and overall performed well. Analysis of heterosis revealed significant heterosis in all three crosses for better parent and standard parent (Table 1). Transgressive segregation illustrates the emergence of individuals in the offspring of a hybrid that outperform either of the parents in terms of one or more characteristics. The segregants emerged with different frequency and may perform positively or negatively depends on traits of interest due to the complementation of additive alleles, epistatic interactions of unique parental attributes, unmasking of recessive alleles from a heterozygous parent, or any combination of these mechanisms. Therefore, the frequency of transgressive segregants was estimated for all the three crosses and is presented in Table 2.
Plant height
The data indicated that the maximum heterobeltiosis (16.62%) and standard heterosis (23.48%) for plant height were observed in cross IC 632961 × Arka Sukomal, while the minimum per cent (8.94% and 15.35% respectively) were observed in cross Arka Arjun × IC 632961 (Table 1). TGS were determined based on values exceeding those of the lower parent, which was considered as the better parent (Arka Arjun). A high frequency of transgressive segregants (21.95%) was observed in the F
2 plants derived from the cross IC 632961 × Arka Arjun (Table 2). It is observed that transgressive segregations are frequently noticed in crossing of diverse crosses
i.e., IC 632961 and Arka Arjun French bean leads to increase in plant height. Genesists explained it as accumulation of genes from both parents and subsequent recombination in segregating generations.
Leaf length and leaf width
The maximum better parent heterosis (32.9%, 28.06%) and economic heterosis (51.7%, 88.54%) were observed in cross IC 632961 × Arka Arjun while the minimum percentages were estimated in cross IC 632961 × Arka Sukomal (Table 1). Regarding the TGS, the maximum frequency (48.72% and 41.03%) for leaf length and width respectively was reported in the F
2 plants of cross IC 632961 × Arka Sukomal as presented in Table 2. The IC 632961 is a primitive cultivar grown in Kandhamal district of Odisha projected higher transgressive segregants when crossed with Arka Sukomal which insisted earlier findings that crosses involve domestic lines commonly witnessed transgressive segregation
(Rieseberg et al., 1999).
Leaf area
Significantly, the maximum heterobeltiosis (38.22%) and the standard heterosis (74.92%) were estimated for the leaf area in cross IC 632961 × Arka Arjun whereas, the minimum value was observed in IC 632961 × Arka Sukomal. In contrast, the highest TGS (43.59%) were observed in IC 632961 × Arka Sukomal (Table 2) as both the parents having bigger leaf size where the overdominance or non-additivity of allelic interaction within a locus may be contributed.
Days to 50% flowering
For earliness negative heterosis is desirable to obtain segregants that flower earlier compared to parent. The cross IC 632961 × Arka Sukomal showed a significantly minimum heterosisbeltiosis (-13.51%) than other cross combination. For TGS estimation, the value of the lower parent value was considered and the maximum frequency TGS (15.38%) was observed in cross IC 632961 × Arka Sukomal followed by 12.2% and 3.08% in cross IC 632961 × Arka Arjun and Arka Arjun × IC 632961 respectively in F
2 generation which may be due to non-additivity allelic interaction between loci or epistasis. Reports confirmed that transgressive segregation shown elevating potential premating barriers like flowering time in pigeon pea (Srivastava and Saxena, 2019). The results were in conformity with
Aditya et al., (2013) in soybean crosses and Kshirsagar
et al. (2013) in tomato who reported transgressive segregation for days to first flowering in F
3 generation.
Number of inflorescences
Significantly higher percentages of heterosis for inflorescences (32.35% and 28.57%) were found in the better parent and standard parent, respectively, in cross IC 632961 × Arka Sukomal, whereas in the cross Arka Arjun × IC 632961, the difference was non-significant. Regarding transgressive segregants, the F
2 plants exhibited a higher percentage of transgressive segregants in reciprocal cross combination
i.e., IC 632961 × Arka Arjun (79.49%) and Arka Arjun × IC 632961 (69.23%) explained cross between two diverse parents
i.e., IC 632961 (pole type) and Arka Arjun (bush type) with additive and additive × additive epistatic allelic interactions along with dominance effects lead to increase in inflorescence counts in segregating generations.
Pod length and pod width
Due to the low heritability observed for pod length and pod width in French bean, the heterosis was found to be non-significant for all crosses. However, significant standard heterosis (29.32% and 33.53%) was observed (Table 1). The cross IC 632962 × Arka Arjun showed moderate heterosis in comparison to the better parent. The data on TGS on pod length depicted that the cross combination; IC 632961 × Arka Sukomal observed with maximum number of TGS (71.79%) may be due to involvement of overdominance effects as both the parents expressed longer pods phenotypically which was not observed in cross; Arka Arjun × IC 632961 (TGS = 0) (Table 2). As far pod width is concerned less percentage of TGS were observed in all crosses due to low heritability.
Number of pods
Significantly, higher positive heterobeltiosis (33.33%) was estimated in cross IC 632961 × Arka Sukomal and standard heterosis (52.63%) was observed in cross IC 632962 × Arka Arjun resulting in the maximum emergence of TGS (78.46%) for number of pods plant
-1 followed by IC 632961 × Arka Sukomal (76.92%). The results explained the evaluation of TGS is due to accumulation of favourable genes and complementary action of additive alleles that are dispersed between the parental lines (
Reddy and Singh, 1989).
Shirkole (2006) and Kshirsagar
et al. (2013) worked on tomato interparietal crossing reported higher transgressive segregation for pod number in F
3 generation.
Pod weight and pod yield
The cross IC 632962 × Arka Arjun exhibited maximum heterobeltiosis (29.44% and 78.09%) and standard heterosis (44.96% and 79.61%) for average pod weight and yield per plant, respectively. Additionally, the same cross combination showed the highest percentage of TGS (68.29% and 75.61% respectively) due to the presence of high heterosis, involvement of complementary genes action and additive gene action and fixing of those genes in homozygous state as
prima facie evidence of emergence of transgressive segregants in such polygenic quantitative traits. The findings were in accordance with
Radkov (1980) who inferred that accumulation of plus genes during F
2 and F
3 generations in French bean leads to evaluation of higher transgressive segregants for pod yield per plant. Results are also inconformity with
Kshirsagar et al., (2013) reported transgressive segregation for average fruit weight and yield per plant in F
3 generation of two inter varietal crosses in tomato.
Pod dry weight
In terms of fresh pod weight, the cross IC 632962 × Arka Arjun exhibited maximum positive heterosis in the better parents (20.93% and 46.42%) and the standard parent (20.80% and 103.42%) for average pod dry weight and pod dry weight per plant, respectively. This cross combination also showed a high frequency of TGS (58.54% and 60.98% respectively) due to high heterosis and fixing of dominance × dominance and additive × additive interactions in F
2.
Number of seeds per pod
The data revealed negative or non-significant heterosis in the F
1 generation for the three crosses, indicating non-additive genetic effects for the number of seeds per pod. However, the cross IC 632962 × Arka Arjun exhibited the highest positive standard heterosis (32.04%) and the maximum frequency of TGS (39.02%) which attributed to accumulation of favourable genes or nonadditive gene actions or epistasis.
Seed index
The trait examined in the study showed negative or non-significant heterobeltiosis for seed index
i.e., hundred seed weight in all cross combination whereas, the cross-combination Arka Arjun × IC 632961 and IC 632962 × Arka Arjun exhibited positive heterosis (22.48% and 29.49% respectively) for the standard parent (Table 1). However, for TGS estimation, maximum frequency (43.59%) was reported in the cross IC 632961 × Arka Sukomal (Table 2). This indicated the recombination of genes from both the parents with positive effects resulted emergence of transgressive segregants in groundnut
(Byadagi et al., 2019).
Seed yield
The data on seed yield per plant displayed maximum significant positive heterobeltiosis (33.82%) and economic heterosis (410.64%) in cross IC 632961 × Arka Arjun. On the other hand, IC 632961 × Arka Sukomal and Arka Arjun × IC 632961 displayed negative heterosis for better parent but displayed high economic heterosis (Table 1). TGS identification revealed maximum frequency of 64.62% witnessed in cross combination Arka Arjun × IC 632961 (Table 2). The results corroborated with finding of
Radkov (1980) revealed higher transgressive segregants in seed yield per plant due to accumulation of plus genes in French bean during F
2 and F
3 generations. This indicating that the parents involved in developing F
3 families derived were differed for many genes which causes large amount of genetic variability for yield and its contributing traits
(Shivakumar et al., 2013).
The results on heterobeltiosis corroborated with findings
Chinapolaiah et al., (2019) who revealed high heterotic effect on plant traits such as days to 50% flowering, pod length, pod weight, dry pod yield per plant and seed yield per plant in velvet bean.
Patil et al., (2012) revealed high heterosis in crosses of vegetable lab lab bean for number of pods and green pod yield per plant. The findings regarding transgressive segregants in French bean during the early segregating generation (F
2) align with the findings of previous studies conducted by various authors. Geneticists have proposed that when heterozygous hybrids are self-pollinated and progressed to subsequent segregating generations, they undergo a transition from heterozygosity to homozygosity. During this transition, a rare combination of genes inherited from both parents can contribute to the occurrence of transgressive segregations in later generations. The individuals receiving ‘plus’ alleles from both the parents or ‘minus’ alleles from both the parents are likely to have extreme phenotypes.
Khrostovska et al., (1975) explained parents possess favourable alleles and genes governing economic traits witnessed transgressive segregation in pea crosses across eight segregating generations.
Radkov (1980) considered pod weight and seed yield for estimation of TGS in F
2 and F
3 population of French bean.
Monpara et al., (2004) conducted a study to investigate transgressive segregants in the F
2 generation of French bean for traits such as plant height, pods per plant and pod yield per plant. The researchers concluded that the emergence of transgressive segregants in these traits can be attributed to the contribution of different alleles from the parental lines. Maximum number of transgressive segregants was isolated for number of pods per plant and number of seeds per plant in F
2 and F
3 generation of chick peas
(Sundaram et al., 2023). In an experiment,
Basanagouda et al., (2022) revealed higher transgressive RILs in crosses of dolichos bean for the concerned traits like number of branches per plant, number of pods per plant and seed weight per plant.
Principal component analysis
Principal component analysis (PCA) is used for multivariate analysis to estimate and decompose complicated and large datasets. In this study, PCA was employed to investigate the pattern of variation in F
2 populations, including three parents and a standard check. The analysis was based on the correlation between the studied traits and the extracted clusters were assessed to understand the diversity of genotypes and their relationship with the observed traits. All the examined yield and yield-related traits were subjected to PCA, resulting in a total of 16 principal components (PCs). However, only five of these components were considered significant as they had eigenvalues greater than 1 (Table 3). The length and colour intensity of a vector in a biplot indicate, respectively, the quality’s representation and its contribution to the principal components. In the biplot, the angles between the vectors derived from the midpoint demonstrate the independence or relationship between the qualities being studied for Groups I and III. Positive angles (between I and II) suggest a positive interaction, while negative angles (between I and IV) indicate a negative interaction. Additionally, the larger circles represent the centroids of the corresponding clusters (Fig 1). Taking into account PC1 and PC2 simultaneously, we identified three distinct sets of traits. Group I consisted of NIP and NIP, while group II included LL, LW, LA, PYP, SYP and PDWP. Group III comprised PL, PW, APW, NSP, HSW and APDW and group IV consisted of PH and DF (Fig 1). Notably, the PCA biplot revealed a strong association between group I and II traits, which had a significant contribution to PC1 and the individuals belonging to row clusters 1 and 4. The traits in group III had a greater impact on PC2 and showed a positive correlation with individuals scattered across clusters 1 to 3. On the other hand, the group IV traits (PH and DF) exhibited strong interactions with group I and II traits, indicating a negative correlation. The individuals scattered across clusters 2 to 4 were closely related to these traits (Fig 2). The results corroborated with findings of
Reddy et al., (2021) for pod length, number of pods per plant, 10 pod weight (g), pod length (cm), number of seeds per pod and yield per plant.
Correlation studies for yield and component traits in F2 plants
The correlation studies depicted that there is maximum significant positive correlation of pod yield per plant with NPP followed by NIP, APW, LA and other relevant traits under study except DF which had significant negative correlation (Fig 3). As far as seed yield per plant is concerned, it had strong correlation with PL, NPP, PYP and PDYP whereas, it has nonsignificant correlation with SI. Days to 50% flowering had nonsignificant negative correlation with most of yield associated traits.