Browsing by Subject "Sorghum -- Genetics"
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Item Carbon and nitrogen assimilation during development of sorghum as related to genotype and water stress(Texas Tech University, 1985-05) Harden, Margarette LWater stress is a major deterrent of grain yield in much of the Great Plains and the world. Grain sorghum is more drought tolerant than other cereals and is grown on vast areas in West Texas. For sorghum to become a more important feed grain crop, then genotypes that are more water efficient and water stress tolerant must be developed. The purpose of this study was to determine the relative contribution of both carbon and nitrogen assimilated prior to flowering to the grain filling process as affected by water stress and genotypic differences. Sorghum genotypes differing in degree of leaf senescence during grain filling were grown in field studies with and without irrigation. At flowering the average sorghum plant had accumulated 63% and 70% of the total dry matter (DM) and nitrogen (N), respectively, of that present at physiological maturity. For the average sorghum plant, 15% and 40% of final grain DM and N, respectively, were due to reallocation from assimilates present at flowering. Significant differences in the assimilation and reallocation of DM and N in the sorghum plants occurred due to water stress and genotype. All water stressed plants relied more heavily on DM and N accumulated by flowering in leaves and stalks to fill the grain than nonstressed plants indicating the severe effect of stress on both photosynthesis and protein synthesis. Both genotypes used existing DM and N present at flowering in addition to absorbing more during grain filling. The senescent plants relied more heavily on reallocation of assimilates from stalks and leaves acquired by flowering to fill the grain than did the nonsenescent plants. Findings from this study should aid in understanding the effects of water stress and genotype selection upon the use of net assimilation and remobilization of DM and N in the grain filling process. The use of established reserves by the grain sorghum plant could be an important mechanism to allow plants to mature if no detrimental effects due to stalk or leaf remobilization occur.Item Evaluation of the effect of the environment on the components of yield and other plant traits from a population of Sorghum bicolor L. Moench(Texas Tech University, 1984-08) Koym, Jeffrey WNot availableItem Gas exchange and water use efficiency of grain sorghum(Texas Tech University, 1990-05) Peng, ShaobingGrain sorghum [Sorghum bicolor (L.) Moench] production is usually confined to environments which are considered too dry and hot for other cereals to be productive. Increasing yield and water use efficiency (WUE) of grain sorghum through identification and utilization of superior germplasm in breeding programs is a major goal in the improvement of this crop. Breeding for increased WUE has been limited by the lack of screening criteria and methods that could be used to select desirable genotypes from large populations under field conditions. This study was conducted to determine whether genotypic differences in WUE and gas exchange traits are present and to determine whether the variation in gas exchange rates and efficiencies reflected the genotypic differences in WUE and thereby, could be used as a screening criteria for identifying genotypes of grain sorghum with higher WUE. Five sorghum genotypes (TX 378, TX 430, SC 35, TX 399, and TX 2741) which are parental lines used in hybrid seed production were tested in the greenhouse and field during 1989 under well watered conditions. In the greenhouse study, individual entries were planted in plastic pots containing 10 kg of sterilized potting mix. The field experiment was conducted on an Amarillo loamy fine sand. In both studies, shoot biomass production, amount of water used, and leaf area development were monitored during die growing season. Water use efficiency was calculated as shoot biomass production per unit water use. Gas exchange measurements were made throughout the vegetative stage on uppermost fully expanded leaves and whole canopy using a portable photosynthesis system. Gas exchange efficiency was expressed as the ratio of photosynthetic rate (A) to transpiration rate (T). The sorghum genotypes exhibited significant variation for A, A/T, shoot biomass production, and WUE. TX 378, TX 430, and SC 35 had higher A, A/T, shoot biomass production, and WUE than TX 399 and TX 2741. No consistent genotypic variation was observed for T or whole plant water use rates. Single leaf measurements of gas exchange traits (A and A/T) reflected single plant and whole canopy WUE differences among the genotypes largely due to the positive correlation between A and shoot biomass production. In addition, there was a positive correlation among the genotypes between leaf area and A. The results indicate that measurements of A and leaf area may be used to select for increased WUE in grain sorghum.Item Genetic control of development traits related to productivity of grain sorghum under various soil water supplies(Texas Tech University, 1987-08) Phipps, Michael RSix inbred lines of grain sorghum (Sorghum bicolor L. Moench) were chosen on the basis of their diversity for several developmental and productivity traits. These parents (3 R-lines and 3 B-lines) were crossed in a complete diallel design (fixed model, without parents) in order to study the inheritance of the developmental and productivity traits. In addition, the 3 R-lines were crossed with 3 A-line counterparts to the B-lines for study of male sterile cytoplasm effects upon these traits. The crosses were performed in a greenhouse by the hand-emasculation method. The 39 F, progenies were grown in the field at Brownfield, Texas in a loamy-sand soil under 100% ETa and 50% Eta irrigation levels in 1985 and 1986. Measurements were conducted for developmental traits and productivity traits. From these measurements, several whole plant water use efficiency traits involving productivity per unit leaf area were calculated. Considerable genetic variation was found for most developmental and productivity traits studied. For some traits, this genetic variation was consistent over irrigation regimes and years. However, for several traits this genetic variation differed among irrigation regimes and years. Most of the genetic variation was accounted for by additive genetic effects for most traits while some traits were also controlled by non-additive genetic effects and a few traits exhibited significant reciprocal and maternal effects. Thus most traits studied can be genetically improved in these lines through breeding although some will require careful choice of both parents in hybrid combinations and many may require selection to be conducted over several environments. Seed number was found to be the predominant grain yield component. Grain yield was closely associated with total above-ground biomass suggesting genetic improvement of harvest index would be difficult. Leaf area was associated with grain yield suggesting that leaf area, rather than number of leaves, has the greater effect upon grain yield.Item Genetic control of gas exchange processes affecting water use efficiency in grain sorghum(Texas Tech University, 1987-08) Kidambi, Saranga PaniFrequently it is noted that genotypes within a crop species do not differ significantly in water use efficiency (WUE). However, recent evidence suggested genetic variation for WUE in wheat (Triticum aestivum L.), indicating a possibility of exercising selection for the improvement in this character. Therefore, the present study was undertaken to investigate: 1. The genetic variation for the gas exchange components (viz., photosynthesis and stomatal conductance) affecting WUE in grain sorghum (Sorghum bicolor L. Moench); 2. To determine the genetic control of these gas exchange processes; and 3. To study the relationships between the growth behavior of sorghum hybrids with their photosynthetic characteristics. For this purpose, I have evaluated 30 hybrids, produced by crossing six parental lines in a complete diallel fashion, under field conditions during 1985 and 1986. In addition, three A-lines were crossed with three R-lines to produce nine more hybrids to investigate the effect of male sterile cytoplasm. All the entries were subjected to varying degrees of water stress by imposing irrigation treatments. Data were collected on gas exchange processes and plant growth parameters on all the genotypes and irrigation treatments throughout the growing season in both years. There was 60% variation among the genotypes for photosynthesis (A), stomatal conductance (g), and A:g ratio, both across the season and in any given sampling time-irrigation level. With moderate water stress, A was reduced more than g, indicating that the initial site of stress sensitivity was at the chloroplast level. As stress intensified, g and A changed in parallel. Genetic analysis of A, g and A:g ratios showed the importance of specific combining ability (SCA) effects in the inheritance pattern of the gas exchange processes. It was also noticed that reciprocal effects, with a substantial contribution of maternal cytoplasmic effects, were important in the inheritance of A. The genotypes also differed significantly in their growth behavior, with a range of 30-40% for leaf area per plant (LA), growth rate (GR), and total dry weight (TDW). There was no consistent relationship between A and each of the growth parameters for all the genotypes. However, some genotypes were identified in both the high and low categories of mean A in which A was strongly associated with LA, GR, and TDW. The results suggested that there is substantial genetic variation for gas exchange processes affecting WUE and that non-additive genetic effects are important in governing their inheritance. Therefore, any breeding method which exploits hybrid vigor should be considered in increasing WUE in grain sorghum. Proper choice of lines used as seed parents should also be used to exploit the maternal effects and the cytoplasm-nuclear interactions in the inheritance of A. The relationship between A and growth parameters among certain genotypes, can be used to increase biomass production.Item Genetic variation, heritability estimates, and yield relationship of pre-flowering and post-flowering drought resistant traits in grain sorghum(Texas Tech University, 1995-05) Mkhabela, Sipho MiltonBreeding for drought-prone environments is constrained by lack of suitable selection indices of drought stress resistance. Genetic improvement in drought stress resistance is dependent on the availability of genetic variation and effectiveness of selection within the variation. The objectives of the study were to determine the genetic variation and estimate heritability of pre-flowering and post-flowering drought resistance traits, and determine the relationships among these traits and between the traits and grain yield in a cross involving two sorghum cultivars with contrasting response to drought stress. Three experiments were conducted over two years. Experiment 1 consisted of 100 F3 families and their corresponding bulk F4 families evaluated for pre-flowering drought response at Lubbock in 1991. The families were developed from the cross of B35 with RTx7000. Panicle exsertion, leaf-rolling, desirability (based on panicle development) and grain yield were used as indicators of pre-flowering drought response. Panicle exsertion showed significant genetic variation in both F3 and F4 families. The estimate of narrow-sense heritability of the panicle exsertion was 28%. This estimate plus a high coefficient of variation for this trait indicate that it may not always be a reliable trait on which to base selection. Leaf-rolling showed no significant difference among families in either generation. Desirability scores were significantly different among F3 families but not among the F4 families. Grain yield was not significantly different among F3 families but significantly different in the F4 families. The lack of significant genetic variation for some of the pre-flowering drought resistance traits was probably due to high variability in moisture stress over the test site which resulted in large experimental errors. However, leaf-rolling, panicle exsertion, and desirability (based on floral abortion and sterility) were significantly correlated with grain yield and among themselves. The simple correlation coefficients were significant (P<0.01) and negative for leaf-rolling (lower=best) and panicle exsertion (r=-0.31), leaf-rolling and grain yield (r=-0.55), panicle exsertion and desirability (r=-0.46), desirability (lower=best) and grain yield (r=-0.73) among the F3 families, and positive for panicle exsertion and grain yield (r=0.41) and leaf rolling and desirability (r=0.51) in these families. The simple correlation coefficients of the F4 families had the same response direction and of relative similar magnitude. These findings indicate that any or all these traits may be very useful as selection indices of pre-flowering drought resistance because all are related to each other and all are related to grain yield and the simple correlation coefficients are in the medium to high range. Experiment 2 consisted of the same 100 bulk F4 family progenies used in experiment 1 along with their corresponding bulk F5 families. The bulk families were evaluated for post-flowering drought response under three different stress environments (dryland, limited and full irrigation ) at Lubbock, Texas, in 1992. The rainfall pattern resulted in only post-flowering stress in all three tests. Significant genetic variation was observed for the stay-green trait and grain yield among the families in both populations in all three tests. The stay-green (high=poorer) trait was positively correlated with grain yield in the limited and dryland test environments. The estimate of narrow-sense heritability of the stay -green trait were 39% for limited, 36% for dryland and 32% for full irrigation environment. These regression estimates were deemed sufficient to justify a breeding and selection program to develop post-flowering drought resistant grain sorghum. Experiment 3 consisted of 88 Fg recombinant inbred lines, one developed per F4 family. The 88 FQ lines were evaluated for post-flowering drought response under five environments in West Texas in 1992. Significant differences were observed among lines for the stay-green trait in each environment. Significant differences were observed for line by environment interaction. The stay-green trait was significantly and positively correlated with grain yield (r=0.15) only in the dryland test. Despite the significant correlation of the stay-green trait with grain yield under dryland environment, the size of the correlation was small and probably of little biological value. The stay-green trait appears to be quite independent of grain yield. Stay-green should be a valuable post-flowering drought resistance trait. It appears from the studies here that the stay-green trait can be successfully manipulated and incorporated into high yielding genetic backgrounds.Item Genotypic Variability For Agronomic and Physiological tTraits in Sorghum (Sorghum bicolor [L.] Moench) with Optimum and Suboptimum Water Levels(Texas Tech University, 1982-05) Sheikh-Mohamed, Abdalla INot Available.Item Heterosis, backcross analysis, and breeding potential of one exotic cultivar for grain yield in sorghum (Sorghum bicolor (L.) Moench)(Texas Tech University, 2002-05) Teme, NiabaLian Tang Ai, a Chinese landrace cultivar donor parent and Tx2783, an elite US restorer parental line and, the recurrent parent, were used to develop BC2 derived lines which were evaluated for grain yield potential. The hypothesis of this research was that some of the BC2 derived lines themselves could have higher grain yield potential in BC2F2 and in hybrid combination with ATx623, respectively, than Tx2783 and the hybrid of ATx623xRTx2783. Grain yield of the derived lines and their hybrids grain yield was normally distributed. Five (3.7%) and 46(32.4%) derived lines (P=0.05) produced significantly higher grain yield than the recurrent parent in limited and fully irrigated combined analysis trials, respectively. In the combined analysis of fully irrigated trials, 132(89.2%) hybrids produced significantly higher grain yield than the recurrent parent hybrid. In the combined full irrigation trials, the average heterosis values was 50% over the midparent, heterosis of the best hybrid over the best parent was 60.2%, the best parent over the mid-parent was 78.0% and the worst hybrid had 23.3% over the mid-parent. Highest heterosis of the best hybrid over the best parent was 90.5% at Halfway 2001. Under full irrigation trials, five, four and nine derived lines, respectively, from Lubbock 2000, 2001 and Halfway 2001, were among the top 10% highest grain producing derived lines while four hybrids from Lubbock 2000, 2001 and Halfway 2001 were consistent in producing high grain yield across environments. Across irrigation levels, four derived lines and two hybrids produced consistently and significantly higher grain yield than the recurrent parent and its hybrid. Three high grain yielding derived lines produced high grain yield in hybrids and were significantly superior to the recurrent parent and its hybrids. Five hybrids from the combined limited trials and 7 hybrids from Lubbock 200l fully irrigated trial produced significantly higher grain yield than the standard commercial hybrid check. When using fully irrigated combined analysis, however, no hybrid produced significantly more grain than the standard commercial hybrid. Other derived lines and hybrids had erratic grain yield distribution. Higher grain yield was expressed at Halfway than at Lubbock. There was a significant low and negative correlation between grain yield and maturity in general. Grain yield of derived lines did not accurately predict well their respective hybrid grain yield in individual environments (trials). However, across environments in full irrigation combined trials, grain yield of derived lines was positively and highly correlated to grain yield of hybrids (r=0.419). Introgression of useful yield genes from Lian Tang Ai into Tx2783 was a success. However, genotype by environment interaction made the selection for high yielding and widely adapted derived lines for hybrid productivity a difficult task.Item Molecular genetic analysis of stay-green, a post-flowering drought resistance trait in grain sorghum (Sorghum bicolor L. Moench)(Texas Tech University, 1995-12) Crasta, Oswald RDrought resistance has been a prime breeding objective in sorghum [Sorghum bicolor (L.) Moench] improvement programs. However, selection for drought resistance traits has been difficult under field conditions because of the large environmental influence and lack of control over intensity and timing of stress. The main objectives were to identify the quantitative trait loci (QTLs) influencing the stay-green trait and yield characteristics, and to study the relationship between the two. Two genotypes, B35 and Tx430, and 96 F7 recombinant inbred lines (RILs) from the cross, B35 X Tx430, were evaluated for the stay-green trait, and yield characteristics under post-flowering drought stress (stress) at two locations during 1993 and 1994. Fully irrigated (control) trials were also conducted at two locations during 1994. The phenotypic evaluation for the stay-green trait showed a heritability of 0.68. The high correlation between stay-green rating and chlorophyll index values (r=-0.86 N=94 P<0.0001) confirmed the validity of visual rating of the stay-green response. The restriction fragment length polymorphism (RFLP) linkage map developed using RILs spanned 1455 cM in 12 linkage associations. Regression analysis identified seven genomic regions significantly (P<0.05) influencing the stay-green rating, explaining 58.5% of phenotypic variability. Five putative QTLs influencing the pooled values of the stay-green trait were identified using the interval mapping method, which explained 58.4% of phenotypic variability. Twelve QTLs influencing grain yield were identified across two locations. Five QTLs influencing yield reduction index (YRI) were identified in each of the two stress environments. At Halfway in 1994, the stay-green trait was positively correlated to YRI. All the stay-green QTLs positively contributed to minimizing YRI (r^=0.75 P<0.0001). Stay-green rating was not correlated with yield at phenotypic level (r=0.036 P<0.7303), but some stay-green markers were associated with significant increase in grain yield. The relationship between stay-green and yield could not be established at Lubbock in 1993, due to the mild stress, which resulted in narrow range of allelic differences in the stay-green rating. The complementary nature of stay-green with high yielding ability provides strong evidence for its role as a drought resistance trait.Item Morphological characteristics and yield of grain sorghum (Sorghum bicolor L. Moench)(Texas Tech University, 1983-08) Bickel, John CNot availableItem Nitrogen assimilation in sorghum genotypes(Texas Tech University, 1979-08) Shau, Sue-HwaNot availableItem Photosynthetic variation in sorghum as affected by water stress(Texas Tech University, 1979-05) Morrisset, Barbara LouiseNot availableItem Photosynthetic variation in sorghum genotypes(Texas Tech University, 1978-05) Leeton, Barbara SmithNot availableItem Response of photosynthesis to genetic differences in sink-source ratios(Texas Tech University, 1985-05) McDonald, Lynn DalePhotosynthetic rates, whether measured on single leaves or whole plants, varied in response to environmental parameters, plant age and sink:source (weight of fruit and stem per unit leaf area) ratios. In this study, five cotton (Gossypium hirsutum L.) and five sorghum (Sorghum bicolor L. Moench) strains, genetically different for sink: source ratios were grown in a common environment. This common environment surrounding each plant provided a standardized environment for photosynthesis across all plants within a sample time and allowed any photosynthetic rate differences to be in response to genetic differences in sink:source ratios. Photos3nithetic rates were measured using 1^C02 gas exchange rates on the uppermost fully expanded main stem leaf of cotton and, prior to flag leaf exsertion, the uppermost collared leaf of sorghum. After flag leaf exsertion, the next lower leaf was used as the sample leaf. Seven measurements were made on cotton commencing 51 days after planting (DAP) and terminating 104 DAP. Four measurements were made on sorghum beginning 40 DAP and terminating 70 DAP. Parameters measured at each sampling date included solar irradiance, leaf and air temperature, and leaf conductance. Correlations between these parameters and photosynthetic rates at each sampling date for both cotton and sorghum were low. Photosynthetic rates for cotton were low at the first sampling date and increased thereafter with significant differences among fruiting types. Following fruit formation, the rate of photosynthesis for the fruiting strains did not change significantly indicating that the chloroplasts were operating at their peak capacity within the surrounding environment. The sink:source ratios increased significantly at each sampling date with significant differences among strains. Photosynthetic rates did not respond to changes in sink:source ratios within each fruiting strain following fruit formation across the season but there was a significant difference in photosynthetic rates among the strains with different sink:source ratios. Photosynthetic rates for sorghum were initially high and declined at each succeeding sampling date in response to leaf age. Sink:source ratios increased significantly across the season with significant differences between strains at each sampling date. With the declining photosynthetic rates across the season, it cannot be concluded that there was a positive photosynthetic rate response to the changing sink: source ratio. At the last sampling date, the fruiting strains with the highest sink:source ratio had the highest photosynthetic rate and, likewise, the nonfruiting strain with the lowest sink:source ratio had the lowest photosjmthetic rate. Among cotton and sorghum strains, there was a photosynthetic rate response to changes in sink:source ratios. This consistency in response suggests that both species reacted similarly to changes in sink:source ratios and that some residual potential for increased photosynthetic rates existed when the plants were in the vegetative stage of development. This residual potential for increased photosynthetic rate increases the difficulty in practicing plant breeding for germplasm with enhanced photos3mthetic potential. The results dictate that many growth parameters must be monitored prior to selection of germplasm with enhanced photosynthetic potential. This may explain some of the failures in past attempts to select for this physiological trait.Item Rooting behavior and soil water extraction of several grain sorghum genotypes(Texas Tech University, 1981-08) Moore, Terry JackNot availableItem Sorghum growth and development as related to genetics and environment(Texas Tech University, 1981-12) Kirk, Terry GeneNot available