Abstract: An 8x8 diallel analysis study on cotton (Gossypium hirsutum L.) was launched at Faculty of Agriculture, Gomal University, D.I.Khan, during, 1996-99 to resolve the type of gene action in the inheritance and expression of some significant quantitative characters like number of seeds boll -1 and staple length in F1 and F2 populations. The analysis of variance revealed that differences among genotypes for these traits were highly significant. The Hayman-Jinks model proved to be completely adequate in case of staple length in both the populations. Even though it is adequate for number of seeds boll -1 in F1 but partially adequate in F2 population.
Introduction
In cotton, fantastic genetic potential still awaits exploitation in our commercial varieties. The conclusions of genetic control of various characteristics under different ecological conditions can divulge the prospects for these attributes as a support to recover the attractive cotton plant for future global competition. With the development of diallel cross analysis as a tool for studying quantitative inheritance, it is possible to explore the direct genetic control of the characters.
Turan (1982) and Murtaza et al. (1995) observed that genetic control of seeds boll-1 was largely accounted for by additive gene effects, nevertheless Singh et al. (1985) and Ahmad et al. (1991) had accomplished over dominance type of gene action. Similarly, Raza et al. (1990), Murtaza et al. (1992) Busharat et al. (1998), Subhan et al. (2000) and Amir et al. (2000) concluded significant additive gene effects with partial dominance for staple length. However gene action like over dominance as model of inheritance for staple length were reported by Rehman (1993), Tariq et al. (1995) and Ahmad et al. (1997).
Materials and Methods
The F1 and F2 populations were developed at Faculty of Agriculture, Gomal University, D.I.Khan during 1996-99 by crossing eight local cultivars belonging to Upland cotton, Gossypium hirsutum L. viz. CYTO 9/91, B-496, SLS-1, Niab-78, NIAB-313/12, B-622, Niab-78, NIAB-313/12, B-622, NIAB-92 and CYTO-11/91. The data on individual plant basis were collected at crop maturity and analyzed for number of seeds boll-1 and staple length in F1 and F2 populations.
The data recorded were statistically analyzed through diallel technique developed by Hayman (1954a, 1954b) and applied by Mather and Jinks (1977).
Results and Discussion
The results for the analysis of variance revealed that the mean genetic differences among the hybrids and their parents are highly significant for the characters studied like number of seeds boll-1 and staple length in F1 and F2 populations.
| Table 1: | Analysis of variance of diallel data for seeds boll-1 and staple length in F1 and F2 populations |
Additive genetic variation seemed to exist for these traits for both the populations as the mean squares due to both male and female parents were significant (P<0.01). The interaction and reciprocal differences among male and female parents were (P>0.05) non-significant, consequently, confirming that only additive gene action was responsible for heritable variation of these characters. Moreover, the reciprocal differences were found to be (P>0.05) non significant. This revealed that maternal effects were not significant in the inheritance of these characters like seeds boll-1 and staple length (Table 1). For that reason, the genotypic differences mentioned above stand excellent and retesting against reciprocal mean square becomes needless. To test the adequacy of additive dominance model for the data set regression analysis was carried out. The analysis of the data (Table 2, 3, 4 and 5) revealed that regression coefficient (b=0.9431±8.7347), (b=0.6150±0.1590) deviated significantly from zero but they were non-significantly different from unity for seeds boll-1, staple length in F1 population and as well as (b=0.8821±0.1270), (b=0.9821±0.0475) in F2 population for the same traits respectively.
The results of analysis of variance for arrays of the traits in study (Table 6) showed that Wr – Vr did differ significantly between the arrays in both the populations except in F2 (seeds boll-1).
| Table 2: | Diallel for seeds per boll (F1 generation) |
| Table 3: | Diallel for staple length (F1 generation) |
| Table 4: | Diallel for seeds per boll (F2 generation) |
| Table 5: | Diallel for staple length (F2 generation) |
| Table 6: | Analysis of variance for arrays |
| **, Highly significant, NS, non-significant | |
| Fig. 1: | Wr/ Vr graph for number of seeds per boll (F1) |
| Fig. 2: | Wr/ Vr graph for number of seeds per boll (F2) |
The Hayman-Jinks model proved to be completely adequate in case of staple length in both the populations. Although it is adequate for number of seeds boll-1in F1 but partially adequate in F2 population. From the relatively distribution of array points along the regression line it was exposed that B-622 (F1) and Cyto-9/91(F2) possessed the most dominant genes for seeds boll-1 while cultivar SLS-1 carried the most recessive genes for this trait in both the populations (Fig. 1 and 2 ).
| Fig. 3: | Wr/ Vr graph for staple length (F1) |
| Fig. 4: | Wr/Vr graph for staple length (F2) |
Furthermore, NIAB-78 (F1) and Niab-92 (F2) contained the maximum dominant genes, whereas Cyto-9/91 possessed the most recessive genes for the trait like staple length in both the populations (Fig. 3 and 4). A perusal of (Fig. 1, 2 and 4) revealed that regression line intercepts the covariance axis above the origin, hence signified additive type of gene action with partial dominance except Fig. 3 in which over dominance was reflected.
These results are in conformity with those of earlier research workers like, Azhar et al. (1994), Murtaza (1995), Busharat et al. (1998, 1999) and Subhan et al. (2000). However findings of some others, over dominance as model for inheritance of staple length and seeds boll-1 were reported by Rehman (1993), Tariq et al. (1995) and Ahmad et al. (1997). This deviation might be due to different varieties with different genetic make up used under different environmental conditions.