1 Background
Due to complex nature of seed yield, studying the mode of inheritance of yield and its component traits is essential for formulation of an effective breeding programme for genetic improvement of any crop like mungbean. Because selection aimed at one trait may lead to negative or positive response on the other trait (s). Hence selection of particular trait could depends on its nature and extent of heritability estimates. One of the best methods for the estimation of genetic parameters is generation mean analysis (GMA), in which epistatic effects could also be estimated. Six basic generations variance components may give an accurate information in relating inheritance. Thus, these components may complete the derived information from means (Mather and Jinks, 1982; Kearsey and Pooni, 1996). The choice of an efficient breeding procedure depends on the knowledge of the genetic controlling system of the character to be selected (Azizi et al., 2006). Growth pattern (erect/ spreading) of the plants is also important and are related to the development of lodging resistance in mungbean. Development of varieties with erect and/ semi-erect growth habit may helps to manipulate the plant density and finally enhance the production and productivity. Keeping the above facts in mind, the present experiment was conducted (1) to test suitability of additive-dominance model (2) to estimate genetic parameters such as gene effects using six basic generations and (3) to study the inheritance pattern of growth habit in mungbean.

2 Results and Discussion
Among all six generations of cross I (Meha/ DMS 03-17-2) (Table 1); BC_1:1, BC_1:2 and F₂ were found earliest flowering than the both parents and F₁, whereas F₂ exhibited late maturity duration than all the five generations. F₁ followed by BC_1:1 and BC_1:2 exhibited superior performances in terms of DM, indicating the possibility to recover the early maturing promising lines. P₁ was noted as shortest plant type, whereas F₂ was the tallest one. BC_1.1 and BC_1.2 were found taller than P₁ but shorter than P₂. The maximum NMS was found in B₁, whereas shortest AIL was noted in P₁. BC_1:1 and F₁ takes second rank for AIL. F₁ exhibited superiority over rest five generations for NPBP, NSBP, NPP, BYP and SYP. However, F₂, BC_1:1 and BC_1:2 exhibited inferiority over both parents and F₁. Likewise in cross II (Meha/ DMS 01-34-2), BC_1.2 was found superior for DFFO, NPP, NSP, HI and SYP over rest five generations. P₁ was noted as superior for DM and PH, whereas P₂ showed superiority for NSBP. The F₁ mean was found greater for NMS with short AIL, SI and BYP. BC_1:1 and F₁ takes second rank for AIL. F₁ exhibited superiority over rest five generations for NPBP, NSBP, NPP, BYP and SYP. However, F₂, BC_1:1 and BC_1:2 exhibited inferiority over both parents and F₁. The maximum mean value was exhibited by BC_1:2 for HI and SYP, however F₁ mean for HI and SYP were recorded smaller than the F₂ and both backcross generations but greater than the both parents.

Table 1 Mean performance of P1, P2, F1, F2, B1 and B2 generations for fourteen agro-morphological traits in cross Meha/ DMS 03-17-2 and Meha/ DMS 01-34-2

Significance of epistasis was detected by both type of (scaling and joint scaling) tests, are presented in Table 2. Barring some exceptions (NMS & NSP in Meha/ DMS 03-17-2 and NSBP & NMS in Meha/ DMS 01-34-2) these test revealed the presence of one or more kinds of epistatic effects were detected for all the agro-morphological traits. Estimates of gene effects with SE of the fitted models for fourteen agro-morp hological traits for both crosses are summarized in Table 3. For clear understanding of direction of generation components involved in inheritance of fourteen agro-morphological traits, the shaded matrix is developed and presented as Figure 1. The mean [m] effect was found significant for all the twelve agro-morphological traits under study in both crosses  (except HI & SYP in Meha/ DMS 01-34-2). For cross I; the traits viz., DFFO, NPBP & NPP exhibited positive and significant additive [d] effect, whereas DM, PH, AIL, NSP, SI, HI & SYP showed significant [d] effect but in negative direction. Similarly, NMS & HI showed positive and significant dominance [h] effect, whereas DFFO, DM, NSBP, AIL, PL & SI showed negative and significant [h] effect.  Rest traits viz., PH, NPBP, NPP, NSP, BYP and SYP showed non-significant [h] effect. Additive x additive [i] interaction was found positive and significant for PH, BYP, HI & SYP, whereas negative significant for DM. Additive x dominance [j] gene effect was found negative only for PH, whereas DFFO, NPBP & NSP exhibited positive and significant [j] gene effect. Dominance x dominance [l] was found positive and significant for all the twelve agro-morphological traits under study except NSBP, NSP & HI. Likewise in cross II, The traits viz., DFFO & NPBP exhibited positive and significant [d] gene effect, whereas DM, PH, NSBP, AIL, PL, HI & SYP showed negative and significant [d] gene effect. Similarly, DFFO & DM showed negative and significant [h] effect, whereas NPBP, NMS, NPP, PL, NSP, SI, BYP, HI & SYP showed positive and significant [h] effect.  Additive x additive [i] interaction was found positive and significant for PH, NPBP, NSP, SI, BYP, HI & SYP, whereas negative and significant for DFFO & DM. Additive x dominance [j] gene effect was found positive and significant for PH, AIL & SI, whereas negative and significant for NPP. Dominance x dominance [l] was found positive and significant for DFFO & DM, whereas negative significant for NPBP, NPP, PL, NSP, BYP, HI & SYP.

Table 2 Scaling and joint scaling test for adequacy of additive-dominance model of fourteen agro-morphological traits in cross Meha/ DMS 03-17-2 and Meha/ DMS 01-34-2

Table 3 Estimates of gene effects with SE of the fitted models for fourteen agro-morphological traits in cross Meha/ DMS 03-17-2 and Meha/ DMS 01-34-2

Figure 1 Shaded matrix for direction of generation components involved in inheritance of fourteen agro-morphological traits

Barring some exceptions, [h] effects were greater than the [d] effects for almost all agro-morphological traits in both crosses, indicated the importance of dominance gene effects for yield and its related agro-morpho logical traits. The negative and positive sign of [i] gene effect showed dispersion and association of alleles in parents, respectively. Therefore, allele association exhibited by both crosses viz., cross I (PH, BYP, HI & SYP) and cross II (PH, AIL, SI) for respective traits, whereas none of the cross showed allele dispersion. The negative significant sign of [d] gene effect was recorded for DM, PH, AIL, HI & SYP in both crosses; NSP & SI in cross I and NSBP & PL in cross II, indicating the involvement of reductive alleles in expression of dominant phenotype. In cross I almost all the traits showed unidirectional dominant, whereas in cross II mostly traits showed ambidirectional dominant, indicating the involvement of both reductive and increasing alleles depending on genetic background of parents. The contribution of dominance gene effects varied with to cross and traits. Similar result was also observed earlier by Gawande et al., (2005) and Azizi et al., (2006). The findings also revealed that one and/ or more type of epistatic interaction involved in inheritance of all the traits under study indicating their complex nature. The similar results were also obtained by Khattak et al., (2004a) for PH;  Khattak et al., (2004b) for NCP, TW & NSP; Patil and Kajjidoni (2005) for DFF, PL & HI; Singh et al., (2007) for DFF, DM, PH, NPBP, NSBP, NPP & SYP; Patel et al., (2012) for DFF, PH & SYP. The [h] and [l] sign was found opposite for DFFO, DM, NPP and PL in both crosses indicating the duplicate type of digenic interaction. Likewise, similar type of digenic interaction was also observed for NSBP, AIL, and SI in cross Meha/ DMS 03-17-2 and for NPBP, NSP, BYP HI and SYP in cross  Meha/ DMS 01-34-2. These findings agreed with the reports of Singh et al. (2006), Aliyu et al., (2007) and Khodambashi et al., (2012) for most of the traits. The duplicate type of epistasis interaction generally hinders the improvement by practicing the selection. Hence, higher magnitude of duplicate type of interaction effect would not be desirable. It may give promising lines for respective traits when selection should be made in delayed after several generations of selection through single seed decent (SSD) till fixation for accumulating the favourable genes. The biparental approach is suggested for the exploitation of these important complex inherited agro-morphological traits to recover/ develop the high yielding mungbean. Besides, NMS exhibited [h] gene effect in both crosses, indicating the dominance gene action in governing NMS, may helpful through recombination breeding for mungbean improvement. NSP in Meha/ DMS 03-17-2 and NSBP in Meha/ DMS 01-34-2 exhibited [d] gene effect, indicating the additive gene action in governing, may give transgressive segregants in early generations.

Spreading growth habit was found dominant over erect in both crosses (Table 4). F₂ and back cross population score also fit the expected 3: 1 and 1:1, respectively for growth habit, indicating that these traits are under the monogenic control and could be easily exploited in mungbean improvement progr- amme. Similar findings were also observed earlier by Khattak et al. (1999) and Sriphadet et al. (2010).

Table 4 Segregation ratio for growth habit in two mungbean crosses

It is observed that the inheritance of yield and its component traits is too much complex and gene action is highly influence by type of genetic/ breeding material used to develop the crosses. The present study suggests the biparental mating and/ or diallel selective mating might be rewarding for mungbean improvement. The monogenic inheritance of growth habit indicated that possibility to develop the ideal plant type for high yield from developed population. 

3 Materials and Methods
Genetics of some important agro-morphological traits of mungbean were studied using the F₁, F₂, BC_1.1 and BC_1.2 of a cross between Meha (spreading growth habit) as female parent (P₁) and DMS 03-17-2 and DMS 01-34-2 (erect growth habit) as male parent (P₂). The parents were selected from previous experiment (Singh et al., 2013) and crossed in to obtain the crosses during kharif, 2012. The F₁ seeds were subjected to back crossing and selfing during summer, 2013. These six basic generations were sown in randomized complete block design (RCBD) with three replications during kharif, 2013. 10 competitive random plants from P₁, P₂ & F₁; 15 plants from BC_1:1 & BC_1:2; 60 plants from F₂ population were randomly selected from each family in each replications, to record the observations for agro-morphological traits viz., plant height (PH), number of primary branches per plant (NPBP), number of secondary branches per plant (NSBP), number of pods per plant (NPP), pod length (PL), number of seeds per pod (NSP), seed index (SI), biological yield per plant (BYP), harvest index (HI) and seed yield per plant (SYP). The traits viz., days to first flower open (DFFO) and days to maturity (DM) were computed on plot basis.

The observed means of the six generations and their standard errors were used to estimate the mid-parent [m], additive [d] and dominance [h] gene effects using the joint scaling test of Mather and Jinks (1982). The adequacy of the simple additive-dominance model (mean, additive, and dominance effects) was determined by χ2 test. Where the simple model proved to be inadequate, additive×additive [i], additive×dom- inance [j] and dominance×dominance [l] were added to the model, as proposed by Mather and Jinks (1982). The significance of genetic parameters (m, [d], [h], [i], [j] and [l]) were tested using t-test. The data were subjected to GMA by using statistical package WINDOSTAT 9.1 version. To confirm the inheritance pattern of plant growth habit, the F₂, BC_1.1 and BC_1.2 were subjected to χ2test.

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