Partitioning of non-additive gene action into dominance and epistatic interaction effects on the inheritance of characters could be congregated through generation mean analysis.
Mather and Jinks (1982) endorsed that generation mean analysis evaluates the extent of dominance and epistatic gene effects in addition to additive gene effects. The individual scaling tests C and D and the genetic parameters
viz., ‘d’, ‘h’, ‘i’ and ‘l’ of additive, dominance, additive × additive, additive × dominance and dominance × dominance respectively was estimated. The scales and their parameters of three crosses
viz., PLM 506 × IC 76417, PLM 506 × IC 76381 and IC 398746 × IC 76417 are presented in Table 2 to 4.
Days to fifty percent flowering
In cross PLM 506 × IC 76381 the significance of both the scales were evidenced, whereas the other two crosses observed significance for scale D alone which indicated the presence of epistatic effects in all the three crosses. Additive (d), additive × additive (i) and dominance × dominance (l) effects were significant for the cross PLM 506 × IC 76417 which indicated the presence of additive-dominance and epistatic gene action for this trait. In cross PLM 506 × IC 76381, dominance (h) and dominance × dominance (l) effects were found significant which suggested the presence of dominance and epistatic component of dominance × dominance type of gene action. Similar findings were also recorded by
Yadav et al., (2017). In the case of cross combination IC 398746 × IC 76417, all the effects
viz., additive (d), dominance (h), additive × additive (i) and dominance × dominance (l) effects were found significant. The results suggested that additive along with epistatic gene action plays key role in this cross for the trait. This was also suggested by
Latha et al., (2018), Panigrahi et al., (2020) and
Ragul et al., (2021).
Plant height
The cross PLM 506 × IC 76381 showed significance in both scales for plant height. while the two other crosses showed significance for scale C alone which explains the inadequacy of simple additive-dominance model. The additive (d) gene effect and dominance × dominance (l) effects were found significant for the cross PLM 506 × IC 76417 which suggested additive and epistatic component of dominance × dominance gene action were involved in controlling this trait. The cross PLM 506 × IC 76381 showed significance for additive (d) and dominance (h) effects, which suggests that the character plant height was controlled by both additive and dominance gene actions in this cross. Similar observations were also reported by
Singh et al., (2007). The dominance (h) and dominance × dominance (l) interaction effect were significant for cross IC 398746 × IC 76417.
Sudhakar et al., (2020) and
Ragul et al., (2021) also reported similar findings for this character. Here dominance component and epistatic component of dominance × dominance were important. Hence, selection can be postponed to later generations after the dominance effects would have diminished.
Number of branches per plant
All the three crosses showed significance for the scale C. PLM 506 × IC 76417 showed significance for additive (d) effect, additive × additive (i) and dominance × dominance (l) effects. It showed the presence of additive and epistatic type of gene actions in the hybrid. PLM 506 × IC 76381 and IC 398746 × IC 76417 recorded significance for additive (d), dominance (h) effects, additive × additive (i) and dominance × dominance (l) components. The results specified that additive and epistatic gene action are predominant in these two crosses. These two crosses indicated complicated nature of inheritance for branches per plant while the third cross observed non-significant dominance (h) effects.
Singh et al., (2007) and
Narasimhulu et al., (2018) also reported similar observations for this trait.
Number of clusters per plant
Two crosses
viz., PLM 506 × IC 76381 and IC 398746 × IC 76417 exhibited significance for both the scales and the cross PLM 506 × IC 76417 showed significance for scale D only. In cross PLM 506 × IC 76417 additive (d) and additive × additive (i) effects were significant which indicated the existence of additive and additive × additive gene action. In the case of PLM 506 × IC 76381 additive (d), additive × additive (i) and dominance × dominance (l) effects were significant. It indicated the presence of additive and epistatic type of gene actions in the hybrid.
Narasimhulu et al., (2018) also documented parallel findings in them study for this trait. The cross IC 398746 × IC 76417 exhibited significance for additive (d), dominance (h) effects, additive × additive (i) and dominance × dominance (l) components which advised that the additive and epistatic gene action has a significant role in this cross.
Number of pods per cluster
Inefficacy of simple additive-dominance model to describe the genetic control of this trait was observed due to the significances of both scales in all the three crosses. PLM506 × IC 76417 recorded significant additive × additive (i) and dominance × dominance (l) interaction effects which implies the influence of epistatic gene action in the hybrid. The cross PLM 506 × IC 76381 recorded significant additive (d), dominance (h), additive × additive (i) and dominance × dominance (l) components. The observations showed the existence of additive together with epistatic gene action in the hybrid for the trait. Similarly, additive and non-additive gene action was reported by
Zubair et al., (2007) and
Latha et al., (2018) in their studies. In cross IC 398746 × IC 76417, dominance (h), additive × additive (i) and dominance × dominance (l) components were significant which indicated the predominant role of dominance coupled with epistatic gene action. This trait limits the scope of further improvement via direct selection. These findings were in congruence with the reports of
Narasimhulu et al., (2018).
Number of pods per plant
Significance of one or more scaling tests suggests the inadequacy of simple additive-dominance model for the crosses. The scaling test showed that the scale D was significant in all three crosses
viz., PLM 506 × IC 76417, PLM 506 × IC 76381 and IC 398746 × IC 76417. In the cross PLM 506 × IC 76417 additive (d) gene effect, additive × additive (i) and dominance × dominance (l) components were found significant. It indicated the presence of additive along with epistatic type of gene actions for the character in this cross. In the case of crosses PLM 506 × IC 76381 and IC 398746 × IC 76417 the components additive (d), dominance (h), additive × additive (i) and dominance × dominance (l) were significant for the trait. It revealed the existence of additive and epistatic type of gene actions. Similar findings were observed by
Yadav et al., (2017),
Vadivel et al., (2019) and
Ragul et al., (2021).
Pod length (cm)
Both the scales reported significance for all the three crosses which indicated the epistatic model in crosses. In the cross PLM 506 × IC 76417 additive (d), dominance (h), additive × additive (i) and dominance × dominance (l) components were significant. It revealed the existence of additive, along with epistatic type of gene actions in this cross. The cross PLM 506 × IC 76381 showed significance for additive (d) gene effect alone suggests the presence of additive gene action in the hybrid. In the case of cross IC 398746 × IC 76417 dominance (h), additive × additive (i) and dominance × dominance (l) components were significant which denotes the presence of dominance and epistatic type of gene actions. Similar results such as the presence of additive and non-additive gene actions for the trait pod length were recorded by
Yadav et al., (2017) and
Latha et al., (2018).
Number of seeds per pod
In scaling test, scale C was significant for all the three crosses whereas for scale D, cross PLM 506 × IC 76381 alone showed significance. Here, in crosses PLM 506 × IC 76417 and PLM 506 × IC 76381, additive × additive (i) gene effect and dominance × dominance (l) gene interaction effect were significant. The results implied that epistatic gene action plays an important role in these two crosses for this trait. Whereas in the case of cross IC 398746 × IC 76417, additive (d), dominance (h), additive × additive (i) and dominance × dominance (l) components were significant. The results revealed that additive and epistatic gene action plays a major role in the hybrid. Similar findings about additive and non-additive gene action were reported by
Zubair et al., (2007) and
Latha et al., (2018) respectively.
Hundred seed weight (g)
Simple additive-dominance model was adequate in the cross PLM 506 × IC 76417, whereas the other two crosses were proved significant for both C and D scale. In cross PLM 506 × IC 76417 additive (d) and dominance (h) effects showed high significance which indicated the additive-dominance gene action. In the cross PLM 506 × IC 76381, additive and dominance components along with epistatic component of additive × additive (i) was also important.
Sudhakar et al., (2020) also reported similar findings for this trait. The cross IC 398746 × IC 76417 showed significance for dominance (h) and dominance × dominance (l) components which indicated that dominance and epistatic component dominance × dominance was prominent for the trait. Similar observations were recorded by
Narasimhulu et al., (2018) for this trait.
Single plant yield (g)
The scaling test revealed significance for scale C and scale D in the two crosses PLM 506 × IC 76381 and IC 398746 × IC 76417. Among the main effects, the (d) additive gene effects were non-significant in all the three hybrids. In the case of PLM 506 × IC 76381 and IC 398746 × IC 76417 dominance effects (h) and dominance × dominance (l) effects showed significance, which indicated the existence of dominance and epistatic gene action for the trait.
Sudhakar et al., (2020) also reported similar findings for this trait. In the case of PLM 506 × IC 76417 additive × additive (i) and dominance × dominance (l) components were proved highly significant. This indicated that epistatic gene action plays a major role in this cross. Similar findings were also addressed by
Yadav et al., (2017) and
Latha et al., (2018).
Percentage of disease infection
The scaling test showed significance for both scale C and D for the crosses PLM 506 × IC 76417 and IC 398746 × IC 76417. Whereas in the hybrid PLM 506 × IC 76381, both C and D scales had no significance which indicated the adequacy of simple additive-dominance model for this cross. The additive and additive × additive components were found significant in the cross PLM 506 × IC 76417 which indicated the existence of additive and epistatic gene action for the character. This cross can be fixed for later generation. Additive and dominance components in cross PLM 506 × IC 76381 showed significance which indicated additive-dominance gene action model. In the case of cross IC 398746 × IC 76417, additive, dominance, additive × additive, dominance × dominance components were found significant. The results indicated that additive-dominance and epistatic gene action plays a major role in this cross.