Analysis of variance and per se performance
The analysis of variance for all the twelve characters studied in each of four crosses is presented in Table 2. The analysis of mean sum of squares between families (crosses) were significant for all the characters studied in all the crosses except for oil content indicating the presence of genetic variability for different traits. The Bartlett’s test for homogeneity of error variances of four crosses indicated that the error variances were homogenous for days to flowering of primary raceme, days to maturity of primary raceme, plant height up to primary raceme, number of nodes up to primary raceme, 100 seed weight and seed yield per plant as these traits showed non-significance chi-square values. Since, the crosses revealed significant mean sum of squares among different generations for different characters so, further analyzed for per se performance and gene action. The mean values of various quantitative traits in different generations from four crosses are depicted in Fig.1. The performance of F1 hybrids exceeded the value of their better parent in positive direction for days to flowering of primary raceme, days to maturity of primary raceme in all four crosses; for length of primary raceme and effective length of primary raceme in JP 104 x JI 433 and SKP 84 x JI 441; for number of effective branches per plant and 100 seed weight in SKP 84 x JI 441; for plant height up to primary raceme and oil content in JP 104 x JI 433 and SKP 84 x JI 433; for number of nodes up to primary raceme in SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; and number of capsules on primary raceme and shelling out turn in SKP 84 x JI 437. None of the F1 exceeded the seed yield per plant over their better parent in positive direction. Similarly, none of the F1 was poorer than its respective poor parent for all the crosses except for number of nodes up to primary raceme in cross JP 104 x JI 433; effective length of primary raceme in cross SKP 84 x JI 437 and SJP 84 x JI 433; seed yield per plant in SKP 84 x JI 437; and oil content in SKP 84 x JI 437 and SKP 84 x JI 441. With respect to days to flowering of primary raceme, days to maturity of primary raceme, plant height up to primary raceme and number of nodes up to primary raceme, parents with low value/per se was considered as better parent, in which the per se performance of F1 was lower than its better parent for plant height up to primary raceme in crosses SKP 84 x JI 437 and SKP 84 x JI 441 and for number of nodes up to primary raceme in cross JP 104 x JI 433, while for days to flowering of primary raceme and days to maturity of primary raceme, none of the F1 per se was lower than its better parent. Further, none of the F1 exceeded the seed yield per plant over their better parent in positive direction. Similarly, none of the F1 was poorer than its respective poor parent for all the crosses except for number of nodes up to primary raceme in cross JP 104 x JI 433; effective length of primary raceme in cross SKP 84 x JI 437 and SKP 84 x JI 433; seed yield per plant in SKP 84 x JI 437; and oil content in SKP 84 x JI 437 and SKP 84 x JI 441. The mean values of various quantitative traits in different generations from nine crosses are depicted in the Fig.1.
Scaling tests and estimation of gene effects
Estimates of scaling tests
Initially, the data were subjected to simple scaling tests A, B, C and D (Table 3 to 14). Significant estimates of one or more of these tests for all the traits in all the crosses except for plant height up to primary raceme in cross SKP 84 x JI 441 indicated the presence of digenic interactions (Table 5). Significance of one or other scaling tests B11, B12, B21, B22, B1s and B2s and X and Y for different traits in almost all crosses indicating the importance of higher order interactions. The scaling test B12 and Y for plant height up to primary raceme; B12 and B21 for length of primary raceme; B12, B21, B22 and X for effective length of primary raceme; B21 for number of capsules on primary raceme; B22 for shelling out turn; B21 and X for 100 seed weight; B11, B12, B21, B22, B1s, X and Y for seed yield per plant and B12, B21, B1s and B2s for oil content were significant in all the four crosses.
Estimates of gene effects
The estimates of 'm' were significant in all four crosses for all the traits studied (Table 3 to 14). The additive [d] gene effect was significant and negative in cross JP 104 x JI 433 for days to maturity of primary raceme, plant height up to primary raceme, number of nodes up to primary raceme, number of effective branches per plant, number of capsules on primary raceme and 100 seed weight; in cross SKP 84 x JI 433 for length of primary raceme, effective length of primary raceme, number of effective branches per plant and number of capsules on primary raceme; in cross SKP 84 x JI 437 for plant height up to primary raceme, length of primary raceme, shelling out turn, 100 seed weight and seed yield per plant; and in cross SKP 84 x JI 441 for plant height up to primary raceme. On the other hand, the additive [d] gene effect was observed significant and positive in cross JP 104 x JI 433 for days to flowering of primary raceme, length of primary raceme and seed yield per plant; in cross SKP 84 x JI 433 for days to flowering of primary raceme, days to maturity of primary raceme, plant height up to primary raceme, shelling out turn, seed yield per plant and oil content; in cross SKP 84 x JI 437 for days to flowering of primary raceme, days to maturity of primary raceme, number of nodes up to primary raceme, number of capsules on primary raceme and oil content; and in cross SKP 84 x JI 441 for days to flowering of primary raceme, length of primary raceme, effective length of primary raceme, shelling out turn, 100 seed weight and seed yield per plant. The dominance [h] gene effect played important role for inheritance of days to flowering of primary raceme, length of primary raceme, effective length of primary raceme, shelling out turn, 100 seed weight, seed yield per plant and oil content in all four crosses viz., JP 104 x JI 433, SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; of days to maturity of primary raceme, plant height up to primary raceme and number of effective branches per plant in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; of number of nodes up to primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 437; and of number of capsules on primary raceme in two crosses JP 104 x JI 433 and SKP 84 x JI 441. When the simple additive-dominance model failed to explain the variation among generation means, a six-parameter model involving three digenic interactions ([i], [j] and [l]) proposed by Hayman (1958) was applied. This model utilized only six basic generation viz., P1, P2, F1, F2, B1 and B2. On the other hand, based on weighted least square technique, digenic and trigenic interaction models were also tested which had additional provision of testing the adequacy of model with six degrees of freedom and two degrees of freedom besides being utilizing means of all the twelve generations, respectively. Further, these models were not adequate for all the traits studied in four crosses in the present study. The significant of 𝜒2(2) value at six degrees of freedom pointed out the presence of higher order gene interactions in all four crosses for all the traits studied. The goodness of fit for six-parameter model of Hayman (1958) could not be tested in the present study owing to no degrees of freedom left for testing chi-square estimates for various characters. Therefore, the perfect fit solution of Hayman (1958) does not provide a general method for testing the adequacy of digenic interaction model. Such a method would require experiment with more number of family means than the minimum number necessary for fitting a full digenic interaction model. Hence, the present study was planned and executed with means of twelve generations and model of Hill (1966) was tested in which six degrees of freedom left for testing the adequacy of six-parameter model of Hill (1966).While fitting trigenic epistatic model, the 𝜒2(3) value at two degrees of freedom were non-significant for effective length of primary raceme in JP 104 x JI 433; for number of effective branches per plant in SKP 84 x JI 441; for number of capsules on primary raceme in two crosses namely, JP 104 x JI 433 and SKP 84 x JI 437 suggesting the adequacy of the trigenic interaction model.
Among digenic interactions, additive x additive [i] gene effect was significant in all four crosses for length of primary raceme and shelling out turn; in crosses SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441 for effective length of primary raceme and seed yield per plant; in crosses JP 104 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441 for number of capsules on primary raceme and oil content; in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 441 for 100 seed weight; in crosses SKP 84 x JI 433 and SKP 84 x JI 437 for days to maturity of primary raceme and number of effective branches per plant; in crosses JP 104 x JI 433 and SKP 84 x JI 437 for number of nodes up to primary raceme; in cross SKP 84 x JI 441 for days to flowering of primary raceme and in cross SKP 84 x JI 437 for plant height up to primary raceme.
Likewise, the estimates of additive x dominance [j] gene effect were significant for days to maturity of primary raceme, shelling out turn, seed yield per plant and oil content in all four crosses, JP 104 x JI 433, SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for days to flowering of primary raceme in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 441; for plant height up to primary raceme and 100 seed weight in crosses JP 104 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for length of primary raceme and number of capsules on primary raceme in JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; for number of nodes up to primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 437; for effective length of primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 433; and for number of effective branches per plant in cross JP 104 x JI 433.
Similarly, dominance x dominance [l] gene effect was observed significant for days to flowering of primary raceme, effective length of primary raceme, number of effective branches per plant, shelling out turn and 100 seed weight in all four crosses JP 104 x JI 433, SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for days to maturity of primary raceme, plant height up to primary raceme and seed yield per plant in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; for length of primary raceme in crosses SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for number of nodes up to primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 437; for number of capsules on primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 441; and for oil content in crosses SKP 84 x JI 433 and SKP 84 x JI 441. This indicated that digenic epistasis interactions had also contributed a sizeable portion of variation in the genetic makeup of various traits.
Trigenic epistasis was significant in various crosses for different characters in the present study. Additive x additive x additive [w] gene effect was observed significant in the present study in all four crosses for plant height up to primary raceme, length of primary raceme, shelling out turn and seed yield per plant; in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437 for days to maturity of primary raceme and number of capsules on primary raceme; in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 441 for days to flowering of primary raceme; in crosses JP 104 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441 for 100 seed weight; in crosses JP 104 x JI 433 and SKP 84 x JI 433 for number of effective branches per plant; in crosses SKP 84 x JI 433 and SKP 84 x JI 441 for effective length of primary raceme; in crosses SKP 84 x JI 433 and SKP 84 x JI 437 for oil content; and in cross JP 104 x JI 433 for number of nodes up to primary raceme.
Moreover, additive x additive x dominance [x] gene effect was significant for number of capsules on primary raceme, shelling out turn and 100 seed weight in all four crosses JP 104 x JI 433, SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for days to flowering of primary raceme in crosses SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for number of effective branches per plant and oil content in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 441; for length of primary raceme in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; for seed yield per plant in crosses JP 104 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for days to maturity of primary raceme, plant height up to primary raceme and effective length of primary raceme in crosses SKP 84 x JI 433 and SKP 84 x JI 437; and for number of nodes up to primary raceme in crosses JP 104 x JI 433 and SKP 84 x JI 441.
On the other hand, additive x dominance x dominance [y] gene effect was significant for plant height up to primary raceme, length of primary raceme, shelling out turn and oil content in all the four crosses, for days to maturity of primary raceme, number of nodes up to primary raceme, 100 seed weight and seed yield per plant in three crosses viz., JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; for effective length up to primary raceme in crosses JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 441; for number of capsules on primary raceme in crosses JP 104 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for days to flowering of primary raceme in crosses, JP 104 x JI 433 and SKP 84 x JI 441; and for number of effective branches per plant in crosses JP 104 x JI 433 and SKP 84 x JI 437.
With respect to dominance x dominance x dominance [z] gene effect, it was noted significant for days to flowering of primary raceme, shelling out turn, seed yield per plant and oil content in all the four crosses; for days to maturity of primary raceme, effective length up to primary raceme and number of effective branches per plant in three crosses viz., JP 104 x JI 433, SKP 84 x JI 433 and SKP 84 x JI 437; for number of capsules on primary raceme and 100 seed weight in crosses SKP 84 x JI 433, SKP 84 x JI 437 and SKP 84 x JI 441; for length of primary raceme in crosses SKP 84 x JI 433 and SKP 84 x JI 437; for plant height up to primary raceme in cross SKP 84 x JI 437; and for number of nodes up to primary raceme in cross JP 104 x JI 433. So, to sum all types of digenic and trigenic interactions was found significant for shelling out turn in two crosses SKP 84 x JI 437 and SKP 84 x JI 441 and for days to maturity of primary raceme in cross SKP 84 x JI 433.
The opposite signs of either two or all the three gene effects viz., dominance [h], dominance x dominance [l] and dominance x dominance x dominance [z] suggests the presence of duplicate type of epistasis. In the present study, duplicate epistasis was reported in all the crosses for all the characters studied when all the three gene effects were considered together. Further, considering only [h] and [l] parameters, two were opposite in all four crosses for all the traits studied except for days to maturity of primary raceme in cross JP 104 x JI 433, that further indicated involvement of largely duplicate type of gene action in the inheritance of seed yield and its component traits.