ESTIMATION OF STANDARD HETEROSIS FOR REPRODUCTIVE TRAITS IN NEWLY SYNTHESIZED TEST RICE (Oryza sativa L.) HYBRIDS

An experiment was carried to estimate heterotic performances of newly developed test hybrids utilizing CMS system during Rabi 2011 using RCBD design. Five known CMS lines and sixteen developed R-lines were crossed through line × tester analysis. Heterosis for days to first flowering varied from 6.23% to 16.35% with a SD of 4.47 meanwhile heterosis for days to 80% flowering varied from -9.24% to 11.04% with a SD of 4.03. Among eighty crosses seventy two were found positive heterosis for days to first flowering but sixty four crosses were found for days to 80% flowering. RG-BU08-016R crosses with IR58025A (-2.68*) and IR62820A (-3.42**) showed significant negative standard heterosis for days to first flowering. Five crosses of IR58025A showed significant negative heterosis with RG-BU 08-005R (3.42*), RG-BU 08-006R (-5.28**), RG-BU 08-013R (-4.129**), RG-BU 08016R (-5.78**), RG-BU 08-018R (-4.06*) for days to 80% flowering. Besides these 4 crosses of IR62820A showed significant negative heterosis with RGBU 08-007R (-2.32*), RG-BU 08-016R (-6.03*), RG-BU 08-018R (-4.58**) followed by GAN 46A/RG-BU 08-006R (-4.58*), BRRI 1A/RG-BU 08-001R (-2.55**) and BRRI 1A/RG-BU 08-006R (-9.24**) resulted significant negative heterosis for days to 80% flowering. Positive heterosis were recorded for IR58025A with RG-BU 08-007R (26.97**), RG-BU 08-0046R (8.77**) and RG-BU 08-105R (14.44**) for PER and RG-BU 08-018R (42.46**), RG-BU 08-046R (112.30**), RG-BU 08-057R (27.46*) for SER. While two R-lines, RG-BU 08-013R (25.41**) and RG-BU 08-057R (7.21*) were found having significant positive heterosis for panicle exertion rate crosses with IR62820A but RG-BU 08-025R (52.82**), RG-BU 08-057R (122.66**) and RG-BU 08-063R (37.38**) were found having significant positive heterosis for SER. IR62820A/RG-BU08-057R showed significant positive heterosis for both panicle and stigma exertion rate. GAN46A/RGBU 08-063R (5.65* & 133.02**) was recorded showing significant positive heterosis for both panicle and stigma exertion rate where. But the crosses of IR68888A was not shown exhibiting a great contribution for panicle and stigma exertion rate except RG-BU08-018R (25.94**). Meanwhile the crosses of BRRI1A was recorded having significant positive heterosis for PER with RG-BU08-005R (13.41**), RG-BU08-007R (5.65*) and RGBU08-097R (25.94**) as well as RG-BU08-007R (133.02**), RG-BU08013R (48.19**) and RG-BU08-038R (29.21*) were recorded having significant positive heterosis for SER.


INTRODUCTION
Heterosis is an important genetic phenomenon, synonymous with hybrid vigour refers to the manifested superiority of the F 1 hybrid resulting from the cross of genetically dissimilar homozygous parents.The best way to utilize heterosis in crop is to produce F 1 hybrids, which possess maximum heterozygosity (Chetia et al., 2000).Heterosis in rice has been known since 1926, its commercial exploitation was demonstrated only when Chinese rice scientists developed commercial rice hybrids with 20 percent yield advancement over semi-dwarf varieties (Sun et al., 2006).Heterosis is estimated to determine the superiority of F 1 over mid parent or better parent or standard check variety (Hien et al., 2007).Moreover yield potentialities of HYV are in static position.
Therefore, there is an ample scope of enhancement of yield potentiality of rice through development of hybrid variety utilizing CMS system in the country.Nonetheless, the geographical location of Bangladesh is quite favorable for hybrid rice production (Banumathy and Thiyagarajan, 2005).Evaluation of heterosis is a crucial part of hybrid breeding.Heterosis will help the breeder to observe superiority of the hybrids in respect of their parents or standard rice varieties.The observation related to heterosis of different characters of rice showed both positive and negative values (Chahal and Gosal, 2008).
Considering above ideas the present investigation was undertaken with the following objectives: (i) to develop short duration variety; (ii) to estimate standard heterosis for panicle and stigma exertion rate and (iii) to estimate standard heterosis for yield in newly synthesized test hybrids.

MATERIALS AND METHODS
The experiment was carried out at the experimental farm, Department of Genetics and Plant Breeding, BSMRAU, Gazipur 1706 during Rabi 2011.The experimental site is located at the centre of Madhupur Tract (24º29 N latitude and 90º26 E longitude) having an elevation of 8.2m from the sea level.The soil type of experimental field belongs to the shallow red brown terrace type under Salna series of Madhupur Tract (AEZ-28) which is characterized by sandy clay with p H value of 6.5. 5 known CMS lines and 16 developed R-lines were crossed through line × tester analysis and 80 test hybrids were developed.These 80 test hybrids were sown in the subsequent generation to assess heterotic performances in randomized complete block design.
Data on the following parameters were recorded from 10 randomly selected plants and on whole plot basis on days to 1 st flowering, days to 80% flowering, panicle exertion rate (%PER), stigma exertion rate (%PER) and finally grain yield.
Data obtained for each character was subjected to the analysis of variance following three replicated randomized complete block design by using MSTAT-C computer software and the analysis of variance for each of the characters was performed by F-test.Mean, range and standard deviation for each character were also estimated for the hybrids performed by Microsoft Excel program 2007.Standard heterosis was calculated as percentage increase or decrease of F 1 mean performance over the check variety.

Estimation of Standard Heterosis
Mean value of check variety and F 1 s in all replications were taken for heterosis estimation.

Estimation of standard heterosis for days to first and 80% flowering
BRRI dhan28 is an outstanding variety due to its fine grain shape and earliness in nature.It is very difficult to find a hybrid earlier to BRRI dhan28 as life cycle of 140 days.Heterosis for days to first flowering varied from -6.23% to 16.35% with a SD of 4.47 meanwhile heterosis for days to 80% flowering varied from -9.24% to 11.04% with a SD of 4.03.Among eighty crosses seventy two crosses were found positive heterosis for days to first flowering but 64 were found for days to 80% flowering.Normally the number of crosses for first flowering and 80% flowering are same but deviation might be due to prolongs flowering period.Some crosses completed their flowering period within 7 days but some crosses took 12-17 days for completion of flowering.This might be due to abiotic factor (effect of photoperiod, temperature and humidity) and inaccuracy of pollination.Biju et al. (2006) observed magnitude of standard heterosis and per se performance of thirty four hybrids and found significant negative heterosis for plant height and days to 50% flowering.Bhave et al. (2002) evaluated thirty-two rice hybrids from two CMS lines for heterosis (mid-parent) and standard heterosis and observed 58.50 to 80.43% heterosis for days to maturity.Ali (2007) while studying on fifty test hybrid demonstrated that hybrid-4 and hybrid-9 exhibited all types of heterosis in desirable direction for most of the characters, especially for days to 80% flowering and days to maturity.Roy (2006) found ten specific cross combinations performed excellent and most promising hybrids showed positive significant negative heterosis for days to 80% flowering and maturity.In fact from this table it might be concluded that there is few possibilities to found test hybrid having a significant negative heterosis compared to BRRI dhan28.Highly significant positive heterosis for panicle and stigma exertion rate indicates greater suitability of the cross combination over check varieties.Among 80 crosses, positive heterosis were recorded for the crosses of IR58025A with RG-BU 08-007R (26.97**),RG-BU 08-0046R (8.77**) and RG-BU 08-105R (14.44**) for panicle exertion rate and RG-BU 08-018R (42.46**),RG-BU 08-046R (112.30**),RG-BU 08-057R (27.46*) for stigma exertion rate.While two R-lines, RG-BU 08-013R (25.41**) and RG-BU 08-057R (7.21*) were found having significant positive heterosis for panicle exertion rate crosses with IR62820A but RG-BU 08-025R (52.82**),RG-BU 08-057R (122.66**) and RG-BU 08-063R (37.38**) were found having significant positive heterosis for stigma exertion rate.Here it is to be noted that IR62820A/RG-BU08-057R showed significant positive heterosis for both

Table 02 .
Estimation of standard heterosis over BRRI dhan28 for days to first flowering in newly developed 80 F 1 hybrids

Table 03 .
Estimates of standard heterosis over BRRI dhan28 for days to days to 80% flowering in newly developed 80 F 1 hybrids