Crop Science 41:1438-1443 (2001)
© 2001 Crop Science Society of America
CROP BREEDING, GENETICS & CYTOLOGY
Genetic Analysis of Seedling Growth under Cold Temperature Stress in Grain Sorghum
Jianming Yu and
Mitchell R. Tuinstra*
Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506
* Corresponding author (mtuinstra{at}bear.agron.ksu.edu)
 |
ABSTRACT
|
|---|
Planting of grain sorghum [Sorghum bicolor (L.) Moench] earlier in the season should contribute to a longer growing season and more effective utilization of late spring and early summer rainfall, but early planting is hindered by poor seedling vigor under cold temperature conditions. Sources of cold tolerance have been identified, but little is known about the inheritance of this trait. This study was conducted to determine combining ability for seedling growth characteristics under cold temperature conditions in genetically diverse sorghum lines using a Design-II mating scheme. Parental lines and hybrids were evaluated under early and normal planting conditions in the field. The traits measured included emergence, emergence index, leaf number, vigor, and dry weight. Significant differences were observed among entries. Among hybrids, these differences were primarily due to effects of general combining ability. These results indicate that general combining ability is more important than specific combining ability in breeding for seedling vigor in sorghum. Heterosis had favorable effects on all seedling traits measured.
|
INTRODUCTION
|
|---|
IN RECENT YEARS, farmers and agronomists have emphasized earlier planting dates for grain sorghum. Early planting should contribute to a longer growing season, more effective utilization of late spring and early summer rainfall, and enhanced yield potential. Sorghum originated in the semi-arid tropics and expresses excellent heat and drought stress tolerance, but generally is susceptible to cold stress and often expresses poor early-season vigor. Therefore, sorghum germplasm with improved cold tolerance will need to be developed to harness these potential benefits of early planting.
Crop production also has shifted from conventional tillage to minimum tillage and no-till strategies. These conditions generally result in a decreased soil temperature at planting, because the crop residue insulates the soil and reflects solar radiation (Wall and Stobbe, 1983). Consequently, cultivars with vigorous early growth also are required to maximize the potential of early planting in these environments.
Sources of cold tolerance have been identified in sorghum (Soujeole and Miller, 1984; Nordquist, 1971; Singh, 1985). Genetic variability for cold tolerance is expressed as variations in germination, emergence, and seedling vigor under early planting conditions. However, little is known about the expression or inheritance of these traits in sorghum. The objective of this study was to evaluate combining ability for seedling growth characteristics under cold temperature conditions in genetically diverse sorghum lines.
|
MATERIALS AND METHODS
|
|---|
The hybrids used in this study were developed by intercrossing four common sorghum seed-parent lines, ‘Wheatland’, SA3042, ‘Redlan’, and TxARG-1, with five diverse pollinator lines, Tx2737, Tx435, P954063, IS4225, and ‘ShanQuiRed’ (SQR), using a Design II mating scheme (Comstock and Robinson, 1952). Seed for all entries was produced in a winter nursery in Puerto Rico.
Parent lines and F1 hybrids were evaluated for seedling growth traits under early and normal planting conditions at experiment field sites in Manhattan, KS, on a Eudora-Muir soil type and Hesston, KS, on a Ladysmith-Goessel soil type in 1999 and 2000 (Table 1). Each experiment was conducted using a randomized complete block design with four replications. Entries were grown in single-row plots (5.08m x 0.76m), and 75 seeds were planted per row. Seeds for each entry were treated with N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (Captan) fungicide at the label rate.
View this table:
[in this window]
[in a new window]
|
Table 1. Average minimum and maximum soil temperatures (5 cm) for 30 d after planting sorghum experiments at Manhattan and Hesston, KS in 1999 and 2000.
|
|
Seedling dry weight (above ground), leaf number, emergence, emergence index, and vigor score were measured to evaluate differences in seedling growth. Stand counts were recorded every other day after planting until no more seedlings emerged. Emergence index, a measurement of rate of emergence, was calculated as described by Smith and Millett (1964) using the formula:
where Ej = emergence on day j, Dj = days after planting, and E = final stand. Final stand counts were taken at 30 d after planting. Ten random plants were harvested (above ground only) from each plot at 30 d after planting and were used to measure the number of fully expanded leaves and to calculate seedling dry weight. Twenty-five days after planting, vigor scores from 1 to 5 (1 = excellent; 5 = poor) were assigned to each plot as described by Maiti (1996).
Analyses of variance and combining ability were carried out per established methods (Hallauer and Miranda, 1988; McIntosh, 1983) using the PROC GLM procedure of the SAS Statistics package (SAS, 1989). Several traits required transformation to improve the homogeneity of the error variance. Data for emergence were transformed by arcsine transformation (Little and Hills, 1978). Data for seedling dry weight were transformed by log10 (mg) logarithmic transformation (Menkir and Larter, 1987). The four environments were considered as random effects. The planting dates and entries were considered as fixed effects. Tests of significance for entry, inbred, male, female, male vs. female, inbred vs. hybrid, hybrid, male general combining ability (GCA), female GCA, and male by female specific combining ability (SCA) for all traits were made by comparison with their respective environmental interaction. All interaction terms were tested against the pooled error. Individual GCA estimates were calculated for all parents as in Beil and Atkins (1967). Standard errors for GCA effects were calculated as SEGCA = {MSml [(m - 1)/mflyr]}1/2 or {MSfl [(f - 1)/mfylr]}1/2 as described by Cox and Frey (1984). Average mid-parent heterosis (MPH) values were tested for significance using the F-test in the analysis of variance. Individual high-parent heterosis (HPH) values were calculated for all traits. Least significant differences (LSDs) for HPH were calculated as for entry mean comparison by LSDHPH = t0.05* [(1 + 1)*MSent*loc/(l*y*r)]1/2.
|
RESULTS
|
|---|
Average minimum and maximum soil temperatures (5 cm) for 30 d after planting at each environment are listed in Table 1. Cold stress experiments were planted at least one month before normal planting dates, and the soil profile temperature was much cooler temperature than those observed in the normal planting date at each location.
A combined analysis was conducted to determine the importance of environment, planting date, and interaction effects. Significant environmental effects were noted for all traits and presumably were affected by variations in temperature, rainfall, and soil type (Table 2). Planting date had a significant impact on most traits (Table 2). In the early plantings, emergence decreased by 37%, emergence index doubled, and seedling growth was retarded (Table 3). Entry by planting date interactions were highly significant and generally more variable than entry by environment interactions for most of the traits studied, suggesting that these entries differed in tolerance to cold temperature stress (Table 2).
View this table:
[in this window]
[in a new window]
|
Table 2. Mean squares from analyses of variance of emergence, leaf number, emergence index, vigor, and dry weight based on data of all sorghum entries at two planting dates grown at two locations in two years.
|
|
View this table:
[in this window]
[in a new window]
|
Table 3. Emergence, leaf number, emergence index, vigor, and dry weight based on data of all sorghum entries grown at two locations in two years.
|
|
Separate analyses of early and normal planting dates were conducted to evaluate differences among entries. Large differences were noted among entries in most traits under both conditions, but usually more variation was observed under early planting than under normal planting (Table 4). Among lines, significant differences were attributed primarily to male parent effects except for emergence, for which contributions from both sides were similar. Analysis of average male versus female effect indicated no significant differences for any trait.
View this table:
[in this window]
[in a new window]
|
Table 4. Mean squares from the analyses of variance for emergence, leaf number, emergence index, vigor, and dry weight of 9 inbred lines and their 20 sorghum hybrids grown under early and normal planting conditions.
|
|
Among parent lines, SQR and IS 4225 generally expressed the best early-season performance (Table 5). Under early planting, emergence values for these two lines were 5 to 27% higher than those of other lines, and emergence index values were 1 to 4 d smaller. These lines also produced greater leaf numbers with a higher dry matter accumulation and a better vigor score in the field. Their performance under normal planting also was better than that of most other lines; however, differences were not as dramatic as under early planting (Table 6). Differences among females were smaller; however, TXARG1, a waxy endosperm type, performed poorly for seeding emergence and growth under early and normal planting conditions.
View this table:
[in this window]
[in a new window]
|
Table 5. Emergence, leaf number, emergence index, vigor, and dry weight of nine inbred sorghum lines and 20 hybrids under early planting conditions grown at two locations in two years.
|
|
View this table:
[in this window]
[in a new window]
|
Table 6. Emergence, leaf number, emergence index, vigor, and dry weight of nine inbred sorghum lines and 20 hybrids under normal planting conditions grown at two locations in two years.
|
|
As indicated by the significant line vs. hybrid effect (i.e., average MPH), hybrids performed better than lines under both early and normal planting conditions (Table 4). Heterosis had a favorable effect on all cold-tolerance traits measured, and hybrids as a group emerged more quickly, produced greater leaf numbers and higher dry-matter accumulation, and had better vigor scores (Table 5).
Significant differences also were noted among hybrids for nearly all traits under early and normal planting (Table 4). Under early planting, most of those differences were associated with male parent effects. The GCA effects for males were significant for leaf number, emergence index, vigor, and dry weight, but not for emergence. Female GCA effects were significant for emergence and leaf number.
Many of the entry by environment and partitioned interaction effects were significant (Table 4). For example, both male and female GCA by environment interactions were significant for emergence under early planting (Table 4). Analysis of the male and female effects estimated in each environment indicated both rank change and scale effects. The male GCA by environment interaction was caused mainly by a change in rank in some locations, and the female GCA by environment interaction was caused primarily by a change in scale. Many other environment interactions were also significant but relatively small compared to the corresponding main effect (Table 4). Analyses of these interactions indicated mostly scale effects.
The SCA effects were evaluated by the male x female interactions and only emergence at normal planting date was significant (Table 4). SCA effects in these genotypes generally were not important.
The male parents SQR and IS4225 exhibited significant and desirable GCA effects in leaf number, emergence index, vigor, and dry weight (Table 7). Under early planting conditions, these parents also had numerically favorable emergence values. Hybrids derived from these two lines generally emerged earlier, had higher final stands, and better seedling growth (Table 5). Tx2737, a standard U.S. pollinator line, was the poorest male parent for cold tolerance (Table 7). Performances of males under normal planting were similar (Table 7), but differences in leaf number were noted. Among females, only Redlan expressed significant and positive GCA effects for emergence under early planting conditions. Wheatland expressed significant and desirable GCA effects for emergence, vigor, and dry weight under normal planting.
View this table:
[in this window]
[in a new window]
|
Table 7. Estimates of general combining ability for emergence, leaf number, emergence index, vigor, and dry weight of nine sorghum inbred lines under early planting and normal planting conditions.
|
|
Individual HPH values were calculated for traits measured under early planting (Table 8). Positive and significant HPH values were noted for leaf number, vigor, and dry weight in many crosses, meaning that hybrids were superior to the better parent involved in each cross. The HPH values for seedling dry weight ranged from 2% to 19%. Generally, heterosis was less pronounced for emergence and emergence index. The HPH values for emergence were significant in all crosses involving Tx2737 and Tx435. Heterosis values in SQR, IS4225, and P954063 derivatives were relatively low, partly because of the relatively high emergence values for these lines. In some TxARG-1 crosses, emergence values of hybrids were lower than those of high parents and resulted in negative HPH values.
View this table:
[in this window]
[in a new window]
|
Table 8. High-parent heterosis for emergence, leaf number, emergence index, vigor, and dry weight of 20 sorghum hybrids under early planting conditions grown at two locations in two years.
|
|
The correlation between GCA values and parent line performance is a measure of the predictability of hybrid performance based on results of the parents (Igartua et al., 1994). Under early planting, the correlation coefficients for the whole set of parents were significant for all traits measured, indicating that cold tolerance of hybrids can be predicted by the parents involved (Table 9). For the female parents, however, significant correlations were detected only for emergence and vigor score. For the male set, all traits except emergence had significant correlations. Among the males, P954063 had a medium emergence value but the lowest GCA effect. Under normal planting, significant correlations between individual GCA and line for emergence, vigor, and leaf number was contributed mainly by female parents.
View this table:
[in this window]
[in a new window]
|
Table 9. Correlation between performance of nine sorghum inbred lines and their general combining ability effects in hybrid combinations.
|
|
|
DISCUSSION
|
|---|
Among the male parent lines, SQR and IS4225 expressed strong early-season vigor. These lines represent outstanding germplasm sources for cold tolerance in sorghum. Combining ability analyses demonstrated the consistency of these two lines in transmitting desirable cold-tolerance traits to their progeny. These results suggested that SQR and IS4225 could be used readily in breeding for cold tolerance in sorghum.
Hybrids were generally more vigorous than inbred parent lines. The results from analysis of heterosis were generally consistent with reports in the literature. The significance of average mid-parent heterosis in analysis of variance and individual HPH demonstrated that heterosis favorably influences cold tolerance of sorghum, particularly in seedling growth. Pesev (1970) considered inheritance of cold tolerance to be rather complex and concluded that the better stand establishment of single crosses over inbreds could be attributed to complementary gene action. Gibson and Schertz (1977) stated that heterosis is expressed as early as the young seedling stage. Soujeole (1985) found little heterosis in sorghum for emergence and emergence index but significant heterosis for seedling dry weight, height, and leaf area.
Given the assumed importance of seed architecture in expression of cold tolerance, female parent effects were expected to be more important than male parent effects in experimental hybrids. Genetic contributions of the female to the seed are 100% in the pericarp, 67% in the endosperm, and 50% in the embryo. The female parent also contributes to 100% of the seed cell cytoplasm. In our study, analysis of variance revealed significant female GCA effects primarily for emergence characteristics. Correlation analysis indicated significant correlation coefficients between GCA and line performance. These results indicated that emergence of hybrids was determined mainly by female parents, which was not surprising. Emergence is influenced strongly by seed quality, which is determined largely by the seed parent. The importance of the maternal effects on germination and emergence at low temperature has been reported in several studies (Pinnell, 1949; Pesev, 1970; Grogan, 1970; Soujeole and Miller, 1984). The genetic contribution of male parents to emergence characteristics was also significant and consistent with reports in the literature (Haskell and Singleton, 1949; Neal, 1949; Grogan, 1970). Male parents generally contributed more to rate of emergence than to stand establishment in these experiments.
Seedling growth and vigor in early-planted experiments were strongly influenced by male parents. Although female parent effects were significant, the male parents contributed more to hybrid seedling vigor than the female parents. This probably reflects the greater diversity in cold tolerance among male parents than female parents included in this study. Additional studies looking at genetically diverse female parent lines would likely demonstrate a similar role for the seed parent in explaining hybrid seedling vigor. The significant male parent GCA effects in expression of seedling vigor in our study agree with the findings of Eagles (1982) in maize (Zea mays L.). The importance of GCA compared to SCA effects was consistent with reports by Moreno-Gonzales (1988) and Revilla et al. (1999).
|
CONCLUSIONS
|
|---|
The male parents SQR and IS4225 represent good germplasm sources for seedling vigor under cold temperature stress and could be used in breeding for cold tolerance in sorghum improvement programs. Both male and female parents contribute to the expression of seedling growth characteristics in sorghum hybrids. General combining ability is more important than specific combining ability in breeding for cold tolerance in sorghum, suggesting that crosses among lines with high GCA effects will form hybrids or base populations with the best cold tolerance. Vigorous pollinators should be developed that contribute to a strong seedling growth under low temperature stress. Similar types of seed parent lines should contribute to high emergence values and strong seedling growth.
|
NOTES
|
|---|
Contribution No. 01-88-J from the Kansas Agric. Exp. Stn.
Received for publication September 5, 2000.
|
REFERENCES
|
|---|
- Beil, G.M., and R.E. Atkins. 1967. Estimates of general and specific combining ability in F1 hybrids for grain yield and its components in grain sorghum, Sorghum vulgare Pers. Crop Sci. 7:225–228.[Abstract/Free Full Text]
- Comstock, R.E., and H.F. Robinson. 1952. Estimation of average dominance of genes. p. 494–516. In J.W. Gowen (ed.) Heterosis. Iowa State College Press, Ames, IA.
- Cox, D.J., and K.J. Frey. 1984. Combining ability and the selection of parents for interspecific oat matings. Crop Sci. 24:963–967.[Abstract/Free Full Text]
- Eagles, H.A. 1982. Inheritance of emergence time and seedling growth at low temperatures in four lines of maize. Theor. Appl. Genet. 62:81–87.[ISI]
- Gibson, P.T., and K.F. Schertz. 1977. Growth analysis of a sorghum hybrid and its parents. Crop Sci. 17:387–391.
- Grogan, C.O. 1970. Genetic variability in maize for germination and seedling growth at low temperatures. Proc. Ann. Corn Sorghum Res. Conf. 25:90–98.
- Hallauer, A.R., and J.B. Miranda Fo. 1988. Quantitative genetics in maize breeding. 2nd ed. Iowa State Univ. Press, Ames, IA.
- Haskell, G., and W.R. Singleton. 1949. Use of controlled low temperature in evaluating the cold hardiness of inbred and hybrid maize. Agron. J. 41:34–40.[Free Full Text]
- Igartua, E., M.P. Gracia, and J.M. Lasa. 1994. Characterization and genetic control of germination-emergence response of grain sorghum to salinity. Euphytica 76:185–193.
- Little, T.M., and F.J. Hills. 1978. Transformation. p. 139–165. In T.M. Little and F.J. Hills (ed.) Agricultural experimentation. John Wiley and Sons, Inc., NY.
- Maiti, R.K. 1996. Germination and seedling establishment. p. 41–98. In R.K. Maiti (ed.) Sorghum science. Science Publishers, Inc., Lebanon, NH.
- McIntosh, M.S. 1983. Analysis of combined experiments. Agron. J. 75: 153–155.[Abstract/Free Full Text]
- Menkir, A., and E.N. Larter. 1987. Emergence and seedling growth of inbred lines of corn at suboptimal root-zone temperatures. Can. J. Plant Sci. 67:409–415.
- Moreno-Gonzales, J. 1988. Diallel crossing system in sets of flint and dent inbred lines of maize (Zea mays L.). Maydica 33:37–49.[ISI]
- Neal, N.P. 1949. Breeding corn for tolerance to cold. Proc. Annu. Corn and Sorghum Res. Conf. 4:68–80.
- Nordquist, P.T. 1971. Use of earliness and cold tolerance in breeding sorghums. Proc. Ann. Corn Sorghum Res. Conf. 26:33–41.
- Pesev, N.V. 1970. Genetic factors affecting maize tolerance to low temperatures at emergence and germination. Theor. Appl. Genet. 40:351–356.
- Pinnell, E.L. 1949. Genetic and environmental factors affecting corn germination at low temperatures. Agron. J. 41:562–569.[Free Full Text]
- Revilla, P., A. Butron, R.A. Malvar, and A. Ordas. 1999. Relationships among kernel weight, early vigor, and growth in maize. Crop Sci. 39:654–658.[Abstract/Free Full Text]
- SAS Institute. 1989. SAS/STAT user's guide, version 6.09, SAS Inst., Cary, NC.
- Singh, S.P. 1985. Sources of cold tolerance in grain sorghum. Can. J. Plant Sci. 65:251–257.
- Smith, P.G., and A.H. Millet. 1964. Germinating and sprouting response of the tomato at low temperatures. J. Am. Soc. Hort. Sci. 84:480–484.
- Soujeole, A.A. 1985. Cold tolerance of sorghum during early germination and early seedling growth. Ph.D. dissertation. Texas A&M Univ., College Station.
- Soujeole, A.A., and F.R. Miller. 1984. Cold tolerance of sorghum during early developmental stages. Proc. Ann. Corn Sorghum Res. Conf. 39:18–32.
- Wall, D.A., and E.H. Stobbe. 1983. The response of eight corn hybrids to zero tillage in Manitoba. Can. J. Plant Sci. 63:753–757.
This article has been cited by other articles:
|
|
|
|
 
C. D. Franks, G. B. Burow, and J. J. Burke
A Comparison of U.S. and Chinese Sorghum Germplasm for Early Season Cold Tolerance
Crop Sci.,
April 25, 2006;
46(3):
1371 - 1376.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
