SUMMARY AND CONCLUSION 5.1. SUMMARY

An investigation was carried out with live different CMS lines and eight restorer genotypes through two field experiments during summer 2007 to summer 2008 at Bangladesh Rice research Institute, Gazipur. The extent of combining ability effects, the magnitude of heterosis and to find

⁰¹¹¹

the relationships among between combining ability and heterosis for different agronomic and yield related characters of parents and their F1 hybrids in rice are estimated.

5.1.1 Combining ability

Selection of parents as well as crosses are generally based on the results of combining ability analysis. However, the over all findings showed both additive and non-additive gene action were predominant

for

the respective traits, but most of the traits were found tinder controlled of non-additive gene action. The analysis of variances carried out for 14 characters indicating the genotypes differed significantly for all the traits studied. the ratio of GCA and SCA variances were found less than unity for most of the characters, except panicle length and number of spikelets panicle" which revealed that both additive and non-additive gene action were predominant for respective traits but the preponderance of non-additive gene action over the additive gene action were found to be important for those traits.

Estimation of combining ability effects of parents and crosses were used for the genetic analysis. Among the five cytoplasmic male sterile (CMS) lines BRR13A was found good general combiner lbr shorter plant height, earliness and panicle length. BRRI9A were also selected as good general combiner for earliness. The CMS line 1132A was identified as good general combiner for grain panicle-' and

114

spikelet fertility (%). 1R73328A and BRRIIA were considered as good general combiner for tiller hiII and panicle plant* But none of the CMS lines were exhibited significant OCA value for yield plant-'. Similarly, out of 8 restorers BRRJ I OR. BRRI I 2R and BRRI I 7R were found in favour of shorter plant height and earliness due to its significant and negative OCA values. Restorers BRRI 12R and BRRII7R were also found as the best general combiner for grain panicke'.

spikelet fertility (%) and yield plant'. BR827R, BR168R and 13R736R were considered as good general combiner for panicle length, primary branch panicle", secondary branch panicle' and number of spikelet panicle-'.

On the other hand, the hybrids 1R73328A/BR736, 1132A18R736R, BRRTI OA/

BR6723-1-1-2R and 1132A!8R6839-41-5-IR were selected as the best specific combiner for yield plant'', spikelet fertility and 1000-grain weight. The combinations BRR131VBRRT I 7R. 1R73328A!BR6723- 1-1 -2R, BRRI9A/8R6839-4 1-5-1 R BRRI I OA./BRI 68R and 1132A/8R827R were identified as good specific combiner for shorter plant height and earliness.

Therefore, the selected parents and crosses could be used to exploitation of heterosis for future hybrid rice breeding programme.

5.1.2 Heterosis

Fourty hybrids and their parents along with two standard check varieties, BRRI dhan33 and BRRI dhan39 were evaluated in the same experiment of combining ability for heterosis study. The standard heterosis and heterosis over mid and better parents were estimated for 14 agronomic and yield related traits. Nature and extent of heteroses over mid parent and better parent; and over checks were found to vary. The hybrids BRRI3A/I3RRIIOR, BRRI3AJBRRII2R, BRRJ3A/BRRI I 7R, BRRI9A/1310839-4 1-5-I R, RRRI9AIBRRI I OR, BRRI9A/I3RRI I 2R and I3RJtJ9A!E3RRI I 7R manifested significant negative desirable heterosis mid parent, better parent and over both standard check varieties for plant height, days to 50% flowering and days to maturity.

On the other hand, the combination 1R73328AJBR]oSR was selected as tile best hybrid for number of tiller hi!l and panicle length due to its higher significant and positive heterosis over check BRRI dhan33. Similarly, the hybrid 1R73328A/BR736R

was

found best heterotic combination for panicle length, primary branch panicle", secondary branch panicle-' and panicle weight in respect of standard heterosis over BRRJ dhan39.

About 50% of crosses were found significant and positive under standard heterosis over both checks for 1000-grain weight. The hybrids.

131M13AIBRRI 1 OR, BRRI3A/BRRI I 2R, I3RR19A/BRRI I 2R, F3RRI9A/13RRI I 7R, 1132A/BR1 2R. I132A/I3RRJ1 7R, BRRI 1 OA/BRRI I 2R and BRRI I OA/BRRI I 7R were considered as the best heterotjc combination for this character due to its highly significant and positive heterosis. Excellent heterotic combinations were found for yield plani' where about 50% cross were possessed significant and positive heterosis over both checks. The hybrid combinations 1132A/8R827R, 1132A/BR736R and RRRJIOA/13R736R were selected as the best yield performer as well as primary and secondary branch panicle-', spikelet panicle' and grain panicle" among the hybrids studies due to those highly significant and positive heterosis over mid parent, better parent and over both checks.

5.1.3 Character associations

The correlation coefficients between

per se

performance, GCA effects, SCA effects of parents and crosses; relationship between combining ability and heterosis for all the agronornic and yield related characters were studied.

The colTelation coefficients between

_{per se}

performance of parent were found

significantly correlated with OCA effects for all the characters studied. On the

other hand, significant and positive correlations were observed between hybrid

performance and SCA effects for most of the characters except primary branch

per panicle and secondary branch per panicle. Results were observed that out of 227 significant and desirable SCA effects 69 were produced by I-high x Low GCA parental combination. Considering the overall heterotic combinations, it was found that out of 208 significant and positive heterotic crosses 83 were of significant GCA effects for both the parents, 91 were of significant for either of the parent and 34 were of non significant GCA effects. In case of better parent heterosis, about 50% heterotic crosses were manifested when both the parents possessed significant GCA effects. In general, it was observed that majority of the significant heterotic crosses were produced due to significant and non- significant as well as from High x Average GCA parental combination for both mid-parent and better parent heterosis..

5.2 Conclusion

On the basis of the findings of the studies, the following conclusions could be made:

Combining ability study involving 51,x8T indicated both additive and non- additive gene actions in the expression of different agrononiic and yield related characters of which non-additive and epistatic gene actions were predominant.

The CMS lines BRRI3A and 1R73328A were considered as the best general combiner for shorter plant height and earliness. The restorer lines BRRII2R and BRRII7R were good general combiners for five traits in desirable direction.

Generally, best general combiners produced the hybrid with best specific combinations.

Hybrid 1132A/BR736R was exhibited significant and desirable SCA effects

for five important yield contributing traits.

CHAPTER VI