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Studies on Heterosis, Residual Heterosis and Inbreeding Depression for Yield and Related Traits in Sorghum (Sorghum bicolor L.)
First Online 29-04-2021|
Methods: The present investigation was carried out to study the heterosis, residual heterosis and inbreeding depression of forty sorghum crosses (F1s and F2s) obtained by crossing of eight restorer lines with five cytoplasmic male sterile lines in Line x Tester mating design in 2013 and 2014. Observations were recorded on morphological traits viz. days to 50% flowering, days to maturity, plant height, flag leaf length, flag leaf width, panicle length, panicle width, panicle weight,1000 seed weight and grain yield per plant.
Result: Among all crosses, ICSA467 x UPC2 and MR750A2 x UPC2 were found to be best for most of the characters. Inbreeding depression was recorded as significantly positive for plant height for most of the crosses indicates the occurrence of transgressive segregants in F2 generation.
Inbreeding is a phenomenon which influence many quantitative traits and increase homozygosity at particular loci with some degree of dominance (Charlesworth and Charlesworth, 1999). There may be two reasons in which increased homozygosity can cause reduced fitness: increased homozygosity for recessive detrimental gene mutations and increased homozygosity for alleles at loci with heterozygote advantage or can be said as overdominance. Deleterious alleles are generally present at low frequencies (mutation-selection balance) in populations, whereas overdominant alleles at a particular locus are maintained at intermediate frequencies by balancing selection (Charlesworth and Willis, 2009). In present study, the experiments were conducted to estimate the effect of heterosis, residual heterosis and inbreeding depresssion on different yield contributing characters for the parental selection and development of high yielding hybrids in sorghum.
MATERIALS AND METHODS
Ten competitive plants were randomly taken, from each treatment/genotype in each replication in both the years. All the selected plants were tagged and observations for all the characters were taken. The means of different characters for the purpose of statistical analysis were calculated on the basis of the individual data recorded for each character, in each replication separately, for each cross. Days to 50% flowering were calculated by counting the number of days between planting when one half of the panicles in a plot reached the half bloom stage. Days to maturity were estimated when more than 90% of grain turned yellow, not more than 5% were green and not more than 2% were in milking stage. The plant height was measured from ground level to the tip of the uppermost leaf of each plant. Panicle length was measured at maturity, from the bottom panicle node to the upper most floret or the tip of panicle. Panicle weight was measured at maturity. Flag leaf length was measured from base to tip and flag leaf width was measured in middle of the leaf. Weight (grams) of one thousand random grains from total grain yield of tagged plants was recorded and mean was worked out. Average weight of grains obtained from ten random plants after threshing and sun drying was recorded. Heterosis expressed as percentage increase or decrease of F1s over better parent was calculated as suggested by Fonseca and Petterson (1968).
Inbreeding depression in F2 was estimated by using the formula given by Kempthorne (1957)
F1= Mean value of F1 progeny.
F2 = Mean value of F2 progeny.
Residual heterosis was calculated by using the formula of Rao (1980):
F2 = Mean value of F2 progeny.
BP= Mean value of better parent.
RESULTS AND DISCUSSION
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.
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