For days to 50% flowering, significant heterobeltiosis was recorded for almost all the crosses while only eight crosses
i.e. MR750A2 × PC5 (-19.35 H, -9.13 RH), ICSA276 × RS29 (-14.25 H, -12.39 RH), MR750A2 × RS29 (-12.90 H, -11.50 RH), ICSA467 × RS29 (-10.71 H, -4.42 RH), ICSA276 × M35-1 (-11.31 H, -8.43 RH), 11A2 × M35-1(-9.09 H, -7.23 RH), MR750A2 × M35-1(-12.73 H, -7.63 RH) and 11A2 × SPV1616 (-11.68 H, -5.31 RH) exhibited residual heterosis which was significantly lower than heterobeltiosis. All combinations exhibited positive values for inbreeding depression with high heterosis indicates the non-additive gene action for this character. Significant estimates of heterobeltiosis for day to maturity were ranged from -1.91 to -7.33 (over thirty two crosses, while significant residual heterosis was recorded only for MR750A2 × CS3541 (-6.64 H, -2.57 RH), ICSA469 × JJ1041 (-5.90 H, -2.30 RH), MR750A2 × JJ1041 (-7.15 H, -2.55 RH) and MR750A2 × SPV1616 (-7.33 H, -2.30 RH) with positive estimates of inbreeding depression (Table 2).
Positive and significant heterobeltiosis, residual heterosis and inbreeding depression for plant height was ranged from 10.91 to 42.84% (over twenty two crosses), 12.12 to 57.49% (over nineteen crosses) and 0.86 to 23.12 (over twenty five crosses), respectively. Most of the crosses among these include UPC2, M35-1 and SPV1616 as pollinator parent
i.e., ICSA467 × UPC2 (30.28 H and 57.29 RH), ICSA469 × UPC2 (24.70 H and 38.45 RH), ICSA276 × UPC2 (17.12 H and 37.34 RH), 11A2 × UPC2 (20.56 H and 38.29 RH), MR750A2 × UPC2 (11.55 H and 37.50 RH), ICSA467 × M35-1 (30.54 H and 41.87 RH), ICSA469 × M35-1 (15.05 H and 23.32 RH), ICSA276 × M35-1 (10.91 H and 21.61 RH), 11A2 × M35-1 (31.02 H and 39.01 RH), MR750A2 × M35-1 (18.53 H and 24.92 RH), ICSA467 × SPV1616 (22.90 H and 41.98 RH), ICSA469 × SPV1616 (21.35 H and 23.60 RH) and ICSA276 × SPV1616 (28.87 H and 41.59 RH) exhibited higher values of residual heterosis over heterobeltiosis with significant inbreeding depression while crosses with CS3541 as pollinator
i.e. ICSA276 × CS3541 (30.00 H and 20.46 RH), 11A2 × CS3541 (42.84 H and 24.06 RH) and MR750A2 × CS3541 (20.77H and 21.64 RH) gave lower residual heterosis values than heterobeltiosis (Table 2). The retention of high heterosis in F2 generation may be result of transgressive segregants and close linkage of some favourable genes controlling this character. High heterosis and positive values of inbreeding depression indicates towards the non-additive gene action for plant height.
For flag leaf length, significant values for heterobeltiosis and residual heterosis were ranged from -8.16 to 18.54% and -13.46 to -41.23%, respectively. Low and negative heterosis may be due to the presence of epistatic gene action or incomplete dominant gene effects. These results were in accordance with
Umakant et al., (2003). In case of flag leaf width, significant heterobeltiosis and residual heterosis were ranged from -9.38 to 19.35% and -10.98 to 13.92%, respectively. Inbreeding depression was found to be non-significant for both the character. The presence of heterosis in the F1 and residual heterosis in F2 generation along with non-significant values of inbreeding depression determines the role of additive gene action. Also, low inbreeding depression may be due to residual heterosis
(Kumar et al., 2004).
For panicle length, positive and significant heterobeltiosis was recorded for ICSA467 × UPC2 (11.77), MR750A2 × UPC2 (13.38), MR750A2 × CSV15 (14.41), ICSA469 × JJ1041 (11.70), ICSA469 × SPV1616 (27.34), ICSA276 × SPV1616 (10.99) and MR750A2 × SPV1616 (18.14), while no positive and significant values were observed for residual heterosis (ranged from -13.63 to -36.60% over twenty two crosses). Significant and negative values for inbreeding depression were observed for almost all the crosses. Significantly positive heterobeltiosis for panicle width was observed for ICSA467 × UPC2 (30.58), 11A2 × UPC2 (28.85), MR750A2 × UPC2 (12.90), MR750A2 × M35-1 (32.41) and MR750A2 × JJ1041 (33.42), while other crosses exhibited negative values. For residual heterosis, all F1s exhibited significantly negative values of residual heterosis and inbreeding depression. For panicle weight positive and significant heterobeltiosis was ranged from 15.82 to 116.92% (over eighteen crosses). Positive and significant residual heterosis was observed in ICSA467 × UPC2 (115.32 RH, 43.54 H, 45.41 ID), 11A2 × UPC2 (21.83 RH, 75.39 H, -23.50 ID) and MR750A2 × UPC2 (34.92 RH, 116.92 H, -37.65 ID) (Table 2). For the crosses having negative and significant estimates of inbreeding depression provide a scope for selection in the F2 population for sorghum improvement. The similar findings were attributed by
Bhatt (2008).
For 1000 seed weight, twenty seven F1 crosses exhibited significant and positive values of heterobeltiosis ranged from 2.67 to 47.66%. However, nineteen crosses gave significantly positive estimates of residual heterosis (ranged from 3.47 to 45.35%) and inbreeding depression (ranged from 0.10 to 3.49). Maximum heterobeltiosis (47.66%) and heterosis (45.35%) with negative estimates of inbreeding depression (-1.50) was recorded in ICSA469 × CS3541. Highest significant heterosis with less inbreeding depression in this cross is indicating the occurrence of additive gene action. There was a decreased pattern of heterosis in F2 generation with positive estimates of inbreeding depression in most of the progenies.
For grain yield range for significantly positive heterosis was estimated from 12.08 to 101.59% (over twenty crosses). Residual heterosis was found to be significantly negative for all the crosses except ICSA467 × UPC2 (30.84 RH, 14.88 H) and MR750A2 × UPC2 (17.59 RH, 101.59 H). Inbreeding depression was recorded negatively significant for most of the progenies (Table 2). Negative values of inbreeding depression may be due to the occurrence of transgressive segregants in the F2 generation. Various degrees of inbreeding depression were earlier reported by
Agarwal and Shrotria (2005) and
Chiang and Smith (1967). Heterosis and inbreeding depression are the result of dominant gene action and heterosis is absent if the traits are governed only by additive gene action (
Hunter and Anderson, 1997). The findings of present study can be use in various breeding programmes of sorghum.