The estimates of gene effects for days to 50 percent flowering in rabi maize were obtained in six parameters model of generation means (Mather and Jinks 1971) involving ten diverse inbred lines. From the study of gene effects of F1 generation early flowering was found to be partially dominant over late flowering. The mean days to 50 percent silking in F2s generally were later than their corresponding F1s. In case of both back crosses (BC1 and BC2) majority of them tended to regress towards their corresponding recurrent parent. Though main gene effects viz, additive and dominance and in epistasis, additive x additive, additive x dominance and dominance x dominance were important but dominance with additive x additive type of gene action played a predominant role in the inbcritance of flowering. A duplicate type of epistasis was observed in majority of the crosses studied. In order to exploit both additive and dominance gene action present in the material few promising single crosses were identified for their further use either directly in heterosis breeding or derive superior inbred lines from advanced generations.
Maize ranks fifth in cereal grain production and occupies a very important position in India Agriculture. It is cultivated over an area of 6 million hectares for food and fodder purposes. Duration of maize variety plays a prominent role in mixed cropping as well as in crop sequence programme. Before considering a maize crop either in the mixed cropping, or in crop sequence it is essential to specify the maize genotype with desired maturity. Generally maximum yield potentials are reported from full season hybrids in rabi condition (Singh 1986). Therefore in the present study genetics of flowering of full season inbreds were felt essential because in maize, days to 50 per cent silking is considered as a means of judging the total duration of the crop. In addition this trait is also used as a synchrony index for flowering to facilitate crossing and also help to decide the male and female parents in the hybridization programme.
Materials and Methods
Study material comprised of six generations viz. P1, P2, F1, F2, BC1 and BC2 of 45 crosses, obtained from ten parents, were sown in two locations. One set was sown at the college farm college of Agriculture, Rajendranagar (location-1) and another set at Maize Research Station, Amberpet (location-2) during rabi 1989-90 in a complete randomized block design with three replications. The parents and F1s in single rows, F2s in four rows while both back crosses (BC1 and BC2) in each of two row plots of 5 meter long were planted. The spacing adopted was 75 cm between rows and 20 cm plant to plant within a row. Data on total plant basis in each entry was recorded for days to 50 per cent silking. Analysis of variance was conducted for plot wise means by pooling all the data. The plot wise data were pooled to get the generation means and variances. To detect presence or absence of inter allelic interaction the scaling tests of A, B and C of Mather (1949) and joint scaling tests of Cavalli (1952) were carried out. Further six parameter models of Mather and Jinks (1971) were applied to determine the relative importance of main (m,d and h) and interaction (I,j and l ) gene effects.
Results and Discussion
Generation means for days to 50 per cent silking were worked out for P1, P2, F1, F2, BC1 and BC2 of 45 crosses at two locations. Simple additive dominance model was found to be inadequate as seen from significant values of either A,B and C or one or both of A or B or C tests for all the 45 F1 crosses at both the locations. Joint scaling test also indicated significant X2 values for all the crosses at one or the other or both locations. Consequently the six parameter model (Mather and Jinks, 1971) was adopted and main effects viz. 1 (additive x additive), j (additive x dominance) and l (dominance x dominance) for both locations were worked out and presented in table 1 and 2. Among 45 F1s, heterosis over better parent (relatively early flowering) was observed for 25F1 crosses at Rajendranagar (Location_1) and for 21 F1 hybrids at Amberpet(Location-2)
The component ‘m’ was positive and significant for all the crosses in both the locations Negative direction or additive gene effects (d) were observed in 29 F1s with eighteen of hem as significant at location 1 and 20 F1s with thirteen of them as significant at location-2. Crosses viz., Mo 17xjl67, Mo 17 xCM119 at location 1 and Mo 17 x CM 119 and Mo 17 x CM 120 at location 2 had maximum number of additive genes responsible for early silking. Similarly 24 F1s out of 40 at location 1 and 26 F1s out of 29 at location 2 exhibited significant negative dominance gene effects with Mo 17 x H 98 and H 100 XJ1 55 at Rajendranagar and Mo 17 xJ155 and Mo 17 x J1 67 at Amberpet possessing maximum number of dominant genes for early silking. Considering both location ‘h’ type of main gene effects played a predominant role followed by ‘d’ type of genes in governing early silking(Table 1&2).
Among the epistatic effects, 20F1s out of 34 for additive x additive gene effects, three F1s out of 14 ‘j’ gene effects at Rajendranagar and 26 out of 27 F1s for ‘I’ type of gene effects and nine out of 19 F1s for ‘l’ type of gene action at Amberpet exhibited negatively significant gene effects and governed early flowering. Crosses viz. Mo 17 x J126, H 100 x J155 at Rajendranagar and Mo17 x J1 55 and Mo 17 x J167 at Amberpet registered highest number genes for early silking through additive x additive type of gen effects. In all majority of the crosses at both locations showed significant negative direction of ‘I’ type of gene interaction for days to early flowering.
The dominance x dominance (1) component for 42 F1s at location-1 and 44 at location-2 possessed opposite sign to that of dominance component(h) while remaining three crosses at location-1 and one cross at location-2 had similar sign.
In India, rabi maize yields are relatively higher compared to kharif Yields (singh 1986). Genetic studies on diverse genotypes were considered desirable for developing a full season hybrid with higher yields. In any planned breeding programme through understanding of genetics of flowering is essential to develop a high yielding hybrid with desired maturity. Therefore, gene effects were worked out through six generation means for days to 50 per cent silking. The experiment consisting of ten parents and 45 each of F1, F2, BC1, and BC1 generation along with four checks were evaluated simultaneously at college farm, college of Agriculture, Rajendranagar (Location-1) and Agricultural Research Station, Amberpet, Hyderabad (Location-2) during rabi season of 1989-90.
Scaling tests with one or the other or both of A, B, and C and X2 values of joint scaling tests found significant for most of the crosses at both locations. This indicated inadequacy of additive dominance model and confirmed the role of epistatic components. Study of various main gene effects through six parameter model of Mather and Jinks (1971) revealed significance of both additive and dominance gene effects with dominance being predominant for days to 50 per cent silking. In the previous studies prepondering dominant gene action governing days to 50 per cent silking was also reported by Anuradha (1988) Ravindranath(1988) and Raghupathi Reddy (1989).
Among epistatic gene effects additive additive (i) type of component played a major role followed by ‘j’ and ‘l’ type of gene effects in governing the inheritance of flowering. The sign of gene effects of ‘l’ and ‘h’ were opposite in majority of the crosses and indicated duplicate type of epistas is however, three crosses at Rajendranagar and one cross at Amberpet, resistered complementary type of epistasis. A predominant role of ‘i’ type of interaction in the inheritance of flowering was reported in the present investigation. This type of statement was also supported by Raghupathi Reddy 91989).
Desirable crosses possessing maximum number of additive genes responsible for early flowering along with high yields were found in crosses viz. Mo 17 xJ167, Mo 17 x CM119 and Mo 17 x CM120 whereas with dominant genes with additive x additive interaction gene effects in Mo 17 x J1 26, H 100 x J155 and Mo 17 xJ155. These crosses therefore can be directly utilized in heterosis breeding to exploit both additive and dominant genes contributing to early flowering clubbed with high yields. Further, advanced generatation of these crosses can also be used to isolate superior lines with more number of accumulated genes responsible for early flowering along with high yields in new recombination’s because of fixable nature of additive genes present in its genetic system.
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